C Library
erl_nif
Library Summary
API functions for an Erlang NIF library.
Description
A NIF library contains native implementation of some functions of an Erlang module. The native implemented functions (NIFs) are called like any other functions without any difference to the caller. A NIF library is built as a dynamically linked library file and loaded in runtime by calling erlang:load_nif/2
.
Use this functionality with extreme care.
A native function is executed as a direct extension of the native code of the VM. Execution is not made in a safe environment. The VM cannot provide the same services as provided when executing Erlang code, such as pre-emptive scheduling or memory protection. If the native function does not behave well, the whole VM will misbehave.
-
A native function that crashes will crash the whole VM.
-
An erroneously implemented native function can cause a VM internal state inconsistency, which can cause a crash of the VM, or miscellaneous misbehaviors of the VM at any point after the call to the native function.
-
A native function doing
lengthy work
before returning degrades responsiveness of the VM, and can cause miscellaneous strange behaviors. Such strange behaviors include, but are not limited to, extreme memory usage, and bad load balancing between schedulers. Strange behaviors that can occur because of lengthy work can also vary between Erlang/OTP releases.
Example
A minimal example of a NIF library can look as follows:
/* niftest.c */ #include <erl_nif.h> static ERL_NIF_TERM hello(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]) { return enif_make_string(env, "Hello world!", ERL_NIF_LATIN1); } static ErlNifFunc nif_funcs[] = { {"hello", 0, hello} }; ERL_NIF_INIT(niftest,nif_funcs,NULL,NULL,NULL,NULL)
The Erlang module can look as follows:
-module(niftest). -export([init/0, hello/0]). -on_load(init/0). init() -> erlang:load_nif("./niftest", 0). hello() -> erlang:nif_error("NIF library not loaded").
Compile and test can look as follows (on Linux):
$> gcc -fPIC -shared -o niftest.so niftest.c -I $ERL_ROOT/usr/include/ $> erl 1> c(niftest). {ok,niftest} 2> niftest:hello(). "Hello world!"
In the example above the on_load
directive is used get function init
called automatically when the module is loaded. Function init
in turn calls erlang:load_nif/2
which loads the NIF library and replaces the hello
function with its native implementation in C. Once loaded, a NIF library is persistent. It will not be unloaded until the module code version that it belongs to is purged.
Each NIF must have an implementation in Erlang to be invoked if the function is called before the NIF library is successfully loaded. A typical such stub implementation is to call erlang:nif_error
which will raise an exception. The Erlang function can also be used as a fallback implementation if the NIF library lacks implementation for some OS or hardware architecture for example.
A NIF does not have to be exported, it can be local to the module. However, unused local stub functions will be optimized away by the compiler, causing loading of the NIF library to fail.
There is a known limitation for Erlang fallback functions of NIFs. Avoid functions involved in traversal of binaries by matching and recursion. If a NIF is loaded over such function, binary arguments to the NIF may get corrupted and cause VM crash or other misbehavior.
Example of such bad fallback function:
skip_until(Byte, <<Byte, Rest/binary>>) -> Rest; skip_until(Byte, <<_, Rest/binary>>) -> skip_until(Byte, Rest).
Functionality
All interaction between NIF code and the Erlang runtime system is performed by calling NIF API functions. Functions exist for the following functionality:
- Read and write Erlang terms
-
Any Erlang terms can be passed to a NIF as function arguments and be returned as function return values. The terms are of C-type
ERL_NIF_TERM
and can only be read or written using API functions. Most functions to read the content of a term are prefixedenif_get_
and usually returntrue
(orfalse
) if the term is of the expected type (or not). The functions to write terms are all prefixedenif_make_
and usually return the createdERL_NIF_TERM
. There are also some functions to query terms, likeenif_is_atom
,enif_is_identical
, andenif_compare
.All terms of type
ERL_NIF_TERM
belong to an environment of typeErlNifEnv
. The lifetime of a term is controlled by the lifetime of its environment object. All API functions that read or write terms has the environment that the term belongs to as the first function argument. - Binaries
-
Terms of type binary are accessed with the help of struct type
ErlNifBinary
, which contains a pointer (data
) to the raw binary data and the length (size
) of the data in bytes. Bothdata
andsize
are read-only and are only to be written using calls to API functions. Instances ofErlNifBinary
are, however, always allocated by the user (usually as local variables).The raw data pointed to by
data
is only mutable after a call toenif_alloc_binary
orenif_realloc_binary
. All other functions that operate on a binary leave the data as read-only. A mutable binary must in the end either be freed withenif_release_binary
or made read-only by transferring it to an Erlang term withenif_make_binary
. However, it does not have to occur in the same NIF call. Read-only binaries do not have to be released.enif_make_new_binary
can be used as a shortcut to allocate and return a binary in the same NIF call.Binaries are sequences of whole bytes. Bitstrings with an arbitrary bit length have no support yet.
- Resource objects
-
The use of resource objects is a safe way to return pointers to native data structures from a NIF. A resource object is only a block of memory allocated with
enif_alloc_resource
. A handle ("safe pointer") to this memory block can then be returned to Erlang by the use ofenif_make_resource
. The term returned byenif_make_resource
is opaque in nature. It can be stored and passed between processes, but the only real end usage is to pass it back as an argument to a NIF. The NIF can then callenif_get_resource
and get back a pointer to the memory block, which is guaranteed to still be valid. A resource object is not deallocated until the last handle term is garbage collected by the VM and the resource is released withenif_release_resource
(not necessarily in that order).All resource objects are created as instances of some resource type. This makes resources from different modules to be distinguishable. A resource type is created by calling
enif_open_resource_type
when a library is loaded. Objects of that resource type can then later be allocated andenif_get_resource
verifies that the resource is of the expected type. A resource type can have a user-supplied destructor function, which is automatically called when resources of that type are released (by either the garbage collector orenif_release_resource
). Resource types are uniquely identified by a supplied name string and the name of the implementing module.The following is a template example of how to create and return a resource object.
ERL_NIF_TERM term; MyStruct* obj = enif_alloc_resource(my_resource_type, sizeof(MyStruct)); /* initialize struct ... */ term = enif_make_resource(env, obj); if (keep_a_reference_of_our_own) { /* store 'obj' in static variable, private data or other resource object */ } else { enif_release_resource(obj); /* resource now only owned by "Erlang" */ } return term;
Notice that once
enif_make_resource
creates the term to return to Erlang, the code can choose to either keep its own native pointer to the allocated struct and release it later, or release it immediately and rely only on the garbage collector to deallocate the resource object eventually when it collects the term.Another use of resource objects is to create binary terms with user-defined memory management.
enif_make_resource_binary
creates a binary term that is connected to a resource object. The destructor of the resource is called when the binary is garbage collected, at which time the binary data can be released. An example of this can be a binary term consisting of data from ammap
'ed file. The destructor can then domunmap
to release the memory region.Resource types support upgrade in runtime by allowing a loaded NIF library to take over an already existing resource type and by that "inherit" all existing objects of that type. The destructor of the new library is thereafter called for the inherited objects and the library with the old destructor function can be safely unloaded. Existing resource objects, of a module that is upgraded, must either be deleted or taken over by the new NIF library. The unloading of a library is postponed as long as there exist resource objects with a destructor function in the library.
- Module upgrade and static data
-
A loaded NIF library is tied to the Erlang module instance that loaded it. If the module is upgraded, the new module instance needs to load its own NIF library (or maybe choose not to). The new module instance can, however, choose to load the exact same NIF library as the old code if it wants to. Sharing the dynamic library means that static data defined by the library is shared as well. To avoid unintentionally shared static data between module instances, each Erlang module version can keep its own private data. This private data can be set when the NIF library is loaded and later retrieved by calling
enif_priv_data
. - Threads and concurrency
-
A NIF is thread-safe without any explicit synchronization as long as it acts as a pure function and only reads the supplied arguments. When you write to a shared state either through static variables or
enif_priv_data
, you need to supply your own explicit synchronization. This includes terms in process independent environments that are shared between threads. Resource objects also require synchronization if you treat them as mutable.The library initialization callbacks
load
andupgrade
are thread-safe even for shared state data. - Version Management
-
When a NIF library is built, information about the NIF API version is compiled into the library. When a NIF library is loaded, the runtime system verifies that the library is of a compatible version.
erl_nif.h
defines the following:ERL_NIF_MAJOR_VERSION
-
Incremented when NIF library incompatible changes are made to the Erlang runtime system. Normally it suffices to recompile the NIF library when the
ERL_NIF_MAJOR_VERSION
has changed, but it can, under rare circumstances, mean that NIF libraries must be slightly modified. If so, this will of course be documented. ERL_NIF_MINOR_VERSION
-
Incremented when new features are added. The runtime system uses the minor version to determine what features to use.
The runtime system normally refuses to load a NIF library if the major versions differ, or if the major versions are equal and the minor version used by the NIF library is greater than the one used by the runtime system. Old NIF libraries with lower major versions are, however, allowed after a bump of the major version during a transition period of two major releases. Such old NIF libraries can however fail if deprecated features are used.
- Time Measurement
-
Support for time measurement in NIF libraries:
- I/O Queues
-
The Erlang nif library contains function for easily working with I/O vectors as used by the unix system call
writev
. The I/O Queue is not thread safe, so some other synchronization mechanism has to be used.SysIOVec
ErlNifIOVec
enif_ioq_create()
enif_ioq_destroy()
enif_ioq_enq_binary()
enif_ioq_enqv()
enif_ioq_deq()
enif_ioq_peek()
enif_ioq_peek_head()
enif_inspect_iovec()
enif_free_iovec()
Typical usage when writing to a file descriptor looks like this:
int writeiovec(ErlNifEnv *env, ERL_NIF_TERM term, ERL_NIF_TERM *tail, ErlNifIOQueue *q, int fd) { ErlNifIOVec vec, *iovec = &vec; SysIOVec *sysiovec; int saved_errno; int iovcnt, n; if (!enif_inspect_iovec(env, 64, term, tail, &iovec)) return -2; if (enif_ioq_size(q) > 0) { /* If the I/O queue contains data we enqueue the iovec and then peek the data to write out of the queue. */ if (!enif_ioq_enqv(q, iovec, 0)) return -3; sysiovec = enif_ioq_peek(q, &iovcnt); } else { /* If the I/O queue is empty we skip the trip through it. */ iovcnt = iovec->iovcnt; sysiovec = iovec->iov; } /* Attempt to write the data */ n = writev(fd, sysiovec, iovcnt); saved_errno = errno; if (enif_ioq_size(q) == 0) { /* If the I/O queue was initially empty we enqueue any remaining data into the queue for writing later. */ if (n >= 0 && !enif_ioq_enqv(q, iovec, n)) return -3; } else { /* Dequeue any data that was written from the queue. */ if (n > 0 && !enif_ioq_deq(q, n, NULL)) return -4; } /* return n, which is either number of bytes written or -1 if some error happened */ errno = saved_errno; return n; }
- Long-running NIFs
-
As mentioned in the
warning
text at the beginning of this manual page, it is of vital importance that a native function returns relatively fast. It is difficult to give an exact maximum amount of time that a native function is allowed to work, but usually a well-behaving native function is to return to its caller within 1 millisecond. This can be achieved using different approaches. If you have full control over the code to execute in the native function, the best approach is to divide the work into multiple chunks of work and call the native function multiple times. This is, however, not always possible, for example when calling third-party libraries.The
enif_consume_timeslice()
function can be used to inform the runtime system about the length of the NIF call. It is typically always to be used unless the NIF executes very fast.If the NIF call is too lengthy, this must be handled in one of the following ways to avoid degraded responsiveness, scheduler load balancing problems, and other strange behaviors:
- Yielding NIF
-
If the functionality of a long-running NIF can be split so that its work can be achieved through a series of shorter NIF calls, the application has two options:
-
Make that series of NIF calls from the Erlang level.
-
Call a NIF that first performs a chunk of the work, then invokes the
enif_schedule_nif
function to schedule another NIF call to perform the next chunk. The final call scheduled in this manner can then return the overall result.
Breaking up a long-running function in this manner enables the VM to regain control between calls to the NIFs.
This approach is always preferred over the other alternatives described below. This both from a performance perspective and a system characteristics perspective.
-
- Threaded NIF
-
This is accomplished by dispatching the work to another thread managed by the NIF library, return from the NIF, and wait for the result. The thread can send the result back to the Erlang process using
enif_send
. Information about thread primitives is provided below. - Dirty NIF
-
A NIF that cannot be split and cannot execute in a millisecond or less is called a "dirty NIF", as it performs work that the ordinary schedulers of the Erlang runtime system cannot handle cleanly. Applications that make use of such functions must indicate to the runtime that the functions are dirty so they can be handled specially. This is handled by executing dirty jobs on a separate set of schedulers called dirty schedulers. A dirty NIF executing on a dirty scheduler does not have the same duration restriction as a normal NIF.
It is important to classify the dirty job correct. An I/O bound job should be classified as such, and a CPU bound job should be classified as such. If you should classify CPU bound jobs as I/O bound jobs, dirty I/O schedulers might starve ordinary schedulers. I/O bound jobs are expected to either block waiting for I/O, and/or spend a limited amount of time moving data.
To schedule a dirty NIF for execution, the application has two options:
-
Set the appropriate flags value for the dirty NIF in its
ErlNifFunc
entry. -
Call
enif_schedule_nif
, pass to it a pointer to the dirty NIF to be executed, and indicate with argumentflags
whether it expects the operation to be CPU-bound or I/O-bound.
A job that alternates between I/O bound and CPU bound can be reclassified and rescheduled using
enif_schedule_nif
so that it executes on the correct type of dirty scheduler at all times. For more information see the documentation of theerl(1)
command line arguments+SDcpu
, and+SDio
.While a process executes a dirty NIF, some operations that communicate with it can take a very long time to complete. Suspend or garbage collection of a process executing a dirty NIF cannot be done until the dirty NIF has returned. Thus, other processes waiting for such operations to complete might have to wait for a very long time. Blocking multi-scheduling, that is, calling
erlang:system_flag(multi_scheduling, block)
, can also take a very long time to complete. This is because all ongoing dirty operations on all dirty schedulers must complete before the block operation can complete.Many operations communicating with a process executing a dirty NIF can, however, complete while it executes the dirty NIF. For example, retrieving information about it through
process_info
, setting its group leader, register/unregister its name, and so on.Termination of a process executing a dirty NIF can only be completed up to a certain point while it executes the dirty NIF. All Erlang resources, such as its registered name and its ETS tables, are released. All links and monitors are triggered. The execution of the NIF is, however, not stopped. The NIF can safely continue execution, allocate heap memory, and so on, but it is of course better to stop executing as soon as possible. The NIF can check whether a current process is alive using
enif_is_current_process_alive
. Communication usingenif_send
andenif_port_command
is also dropped when the sending process is not alive. Deallocation of certain internal resources, such as process heap and process control block, is delayed until the dirty NIF has completed. -
Initialization
ERL_NIF_INIT(MODULE, ErlNifFunc funcs[], load, NULL, upgrade, unload)
-
This is the magic macro to initialize a NIF library. It is to be evaluated in global file scope.
MODULE
is the name of the Erlang module as an identifier without string quotations. It is stringified by the macro.funcs
is a static array of function descriptors for all the implemented NIFs in this library.load
,upgrade
andunload
are pointers to functions. One ofload
orupgrade
is called to initialize the library.unload
is called to release the library. All are described individually below.The fourth argument
NULL
is ignored. It was earlier used for the deprecatedreload
callback which is no longer supported since OTP 20.If compiling a NIF for static inclusion through
--enable-static-nifs
, you must defineSTATIC_ERLANG_NIF
before theERL_NIF_INIT
declaration. int (*load)(ErlNifEnv* caller_env, void** priv_data, ERL_NIF_TERM load_info)
-
load
is called when the NIF library is loaded and no previously loaded library exists for this module.*priv_data
can be set to point to some private data if the library needs to keep a state between NIF calls.enif_priv_data
returns this pointer.*priv_data
is initialized toNULL
whenload
is called.load_info
is the second argument toerlang:load_nif/2
.The library fails to load if
load
returns anything other than0
.load
can beNULL
if initialization is not needed. int (*upgrade)(ErlNifEnv* caller_env, void** priv_data, void** old_priv_data, ERL_NIF_TERM load_info)
-
upgrade
is called when the NIF library is loaded and there is old code of this module with a loaded NIF library.Works as
load
, except that*old_priv_data
already contains the value set by the last call toload
orupgrade
for the old module code.*priv_data
is initialized toNULL
whenupgrade
is called. It is allowed to write to both*priv_data
and*old_priv_data.
The library fails to load if
upgrade
returns anything other than0
or ifupgrade
isNULL
. void (*unload)(ErlNifEnv* caller_env, void* priv_data)
-
unload
is called when the module code that the NIF library belongs to is purged as old. New code of the same module may or may not exist.
Data Types
ERL_NIF_TERM
-
Variables of type
ERL_NIF_TERM
can refer to any Erlang term. This is an opaque type and values of it can only by used either as arguments to API functions or as return values from NIFs. AllERL_NIF_TERM
s belong to an environment (ErlNifEnv
). A term cannot be destructed individually, it is valid until its environment is destructed. ErlNifEnv
-
ErlNifEnv
represents an environment that can host Erlang terms. All terms in an environment are valid as long as the environment is valid.ErlNifEnv
is an opaque type; pointers to it can only be passed on to API functions. Three types of environments exist:- Process bound environment
-
Passed as the first argument to all NIFs. All function arguments passed to a NIF belong to that environment. The return value from a NIF must also be a term belonging to the same environment.
A process bound environment contains transient information about the calling Erlang process. The environment is only valid in the thread where it was supplied as argument until the NIF returns. It is thus useless and dangerous to store pointers to process bound environments between NIF calls.
- Callback environment
-
Passed as the first argument to all the non-NIF callback functions (
load
,upgrade
,unload
,dtor
,down
,stop
anddyncall
). Works like a process bound environment but with a temporary pseudo process that "terminates" when the callback has returned. Terms may be created in this environment but they will only be accessible during the callback. - Process independent environment
-
Created by calling
enif_alloc_env
. This environment can be used to store terms between NIF calls and to send terms withenif_send
. A process independent environment with all its terms is valid until you explicitly invalidate it withenif_free_env
orenif_send
.
All contained terms of a list/tuple/map must belong to the same environment as the list/tuple/map itself. Terms can be copied between environments with
enif_make_copy
. ErlNifFunc
-
typedef struct { const char* name; unsigned arity; ERL_NIF_TERM (*fptr)(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[]); unsigned flags; } ErlNifFunc;
Describes a NIF by its name, arity, and implementation.
fptr
-
A pointer to the function that implements the NIF.
argv
-
Contains the function arguments passed to the NIF.
argc
-
The array length, that is, the function arity.
argv[N-1]
thus denotes the Nth argument to the NIF. Notice that the argumentargc
allows for the same C function to implement several Erlang functions with different arity (but probably with the same name). flags
-
Is
0
for a regular NIF (and so its value can be omitted for statically initializedErlNifFunc
instances).flags
can be used to indicate that the NIF is adirty NIF
that is to be executed on a dirty scheduler thread.If the dirty NIF is expected to be CPU-bound, its
flags
field is to be set toERL_NIF_DIRTY_JOB_CPU_BOUND
orERL_NIF_DIRTY_JOB_IO_BOUND
.NoteIf one of the
ERL_NIF_DIRTY_JOB_*_BOUND
flags is set, and the runtime system has no support for dirty schedulers, the runtime system refuses to load the NIF library.
ErlNifBinary
-
typedef struct { size_t size; unsigned char* data; } ErlNifBinary;
ErlNifBinary
contains transient information about an inspected binary term.data
is a pointer to a buffer ofsize
bytes with the raw content of the binary.Notice that
ErlNifBinary
is a semi-opaque type and you are only allowed to read fieldssize
anddata
. ErlNifBinaryToTerm
-
An enumeration of the options that can be specified to
enif_binary_to_term
. For default behavior, use value0
.When receiving data from untrusted sources, use option
ERL_NIF_BIN2TERM_SAFE
. ErlNifMonitor
-
This is an opaque data type that identifies a monitor.
The nif writer is to provide the memory for storing the monitor when calling
enif_monitor_process
. The address of the data is not stored by the runtime system, soErlNifMonitor
can be used as any other data, it can be copied, moved in memory, forgotten, and so on. To compare two monitors,enif_compare_monitors
must be used. ErlNifPid
-
A process identifier (pid). In contrast to pid terms (instances of
ERL_NIF_TERM
),ErlNifPid
s are self-contained and not bound to anyenvironment
.ErlNifPid
is an opaque type. It can be copied, moved in memory, forgotten, and so on. ErlNifPort
-
A port identifier. In contrast to port ID terms (instances of
ERL_NIF_TERM
),ErlNifPort
s are self-contained and not bound to anyenvironment
.ErlNifPort
is an opaque type. It can be copied, moved in memory, forgotten, and so on. ErlNifResourceType
-
Each instance of
ErlNifResourceType
represents a class of memory-managed resource objects that can be garbage collected. Each resource type has a unique name and a destructor function that is called when objects of its type are released. ErlNifResourceTypeInit
-
typedef struct { ErlNifResourceDtor* dtor; // #1 Destructor ErlNifResourceStop* stop; // #2 Select stop ErlNifResourceDown* down; // #3 Monitor down int members; ErlNifResourceDynCall* dyncall; // #4 Dynamic call } ErlNifResourceTypeInit;
Initialization structure read by
enif_open_resource_type_x
enif_init_resource_type
. ErlNifResourceDtor
-
typedef void ErlNifResourceDtor(ErlNifEnv* caller_env, void* obj);
The function prototype of a resource destructor function.
The
obj
argument is a pointer to the resource. The only allowed use for the resource in the destructor is to access its user data one final time. The destructor is guaranteed to be the last callback before the resource is deallocated. ErlNifResourceDown
-
typedef void ErlNifResourceDown(ErlNifEnv* caller_env, void* obj, ErlNifPid* pid, ErlNifMonitor* mon);
The function prototype of a resource down function, called on the behalf of
enif_monitor_process
.obj
is the resource,pid
is the identity of the monitored process that is exiting, andmon
is the identity of the monitor. ErlNifResourceStop
-
typedef void ErlNifResourceStop(ErlNifEnv* caller_env, void* obj, ErlNifEvent event, int is_direct_call);
The function prototype of a resource stop function, called on the behalf of
enif_select
.obj
is the resource,event
is OS event,is_direct_call
is true if the call is made directly fromenif_select
or false if it is a scheduled call (potentially from another thread). ErlNifResourceDynCall
-
typedef void ErlNifResourceDynCall(ErlNifEnv* caller_env, void* obj, void* call_data);
The function prototype of a dynamic resource call function, called by
enif_dynamic_resource_call
. Argumentobj
is the resource object andcall_data
is the last argument toenif_dynamic_resource_call
passed through. ErlNifCharEncoding
-
typedef enum { ERL_NIF_LATIN1 }ErlNifCharEncoding;
The character encoding used in strings and atoms. The only supported encoding is
ERL_NIF_LATIN1
for ISO Latin-1 (8-bit ASCII). ErlNifSysInfo
-
Used by
enif_system_info
to return information about the runtime system. Contains the same content asErlDrvSysInfo
. ErlNifSInt64
-
A native signed 64-bit integer type.
ErlNifUInt64
-
A native unsigned 64-bit integer type.
ErlNifTime
-
A signed 64-bit integer type for representation of time.
ErlNifTimeUnit
-
An enumeration of time units supported by the NIF API:
ERL_NIF_SEC
- Seconds
ERL_NIF_MSEC
- Milliseconds
ERL_NIF_USEC
- Microseconds
ERL_NIF_NSEC
- Nanoseconds
ErlNifUniqueInteger
-
An enumeration of the properties that can be requested from
enif_make_unique_integer
. For default properties, use value0
.ERL_NIF_UNIQUE_POSITIVE
-
Return only positive integers.
ERL_NIF_UNIQUE_MONOTONIC
-
Return only
strictly monotonically increasing
integer corresponding to creation time.
ErlNifHash
-
An enumeration of the supported hash types that can be generated using
enif_hash
.ERL_NIF_INTERNAL_HASH
-
Non-portable hash function that only guarantees the same hash for the same term within one Erlang VM instance.
It takes 32-bit salt values and generates hashes within
0..2^32-1
. ERL_NIF_PHASH2
-
Portable hash function that gives the same hash for the same Erlang term regardless of machine architecture and ERTS version.
It ignores salt values and generates hashes within
0..2^27-1
.Slower than
ERL_NIF_INTERNAL_HASH.
It corresponds toerlang:phash2/1
.
SysIOVec
-
A system I/O vector, as used by
writev
on Unix andWSASend
on Win32. It is used inErlNifIOVec
and byenif_ioq_peek
. ErlNifIOVec
-
typedef struct { int iovcnt; size_t size; SysIOVec* iov; } ErlNifIOVec;
An I/O vector containing
iovcnt
SysIOVec
s pointing to the data. It is used byenif_inspect_iovec
andenif_ioq_enqv
. ErlNifIOQueueOpts
- Options to configure a
ErlNifIOQueue
.- ERL_NIF_IOQ_NORMAL
Create a normal I/O Queue
Exports
void *enif_alloc( |
Allocates memory of size
bytes.
Returns NULL
if the allocation fails.
The returned pointer is suitably aligned for any built-in type that fit in the allocated memory.
int enif_alloc_binary( |
Allocates a new binary of size size
bytes. Initializes the structure pointed to by bin
to refer to the allocated binary. The binary must either be released by enif_release_binary
or ownership transferred to an Erlang term with enif_make_binary
. An allocated (and owned) ErlNifBinary
can be kept between NIF calls.
If you do not need to reallocate or keep the data alive across NIF calls, consider using enif_make_new_binary
instead as it will allocate small binaries on the process heap when possible.
Returns true
on success, or false
if allocation fails.
ErlNifEnv *enif_alloc_env() | OTP R14B |
Allocates a new process independent environment
. The environment can be used to hold terms that are not bound to any process. Such terms can later be copied to a process environment with enif_make_copy
or be sent to a process as a message with enif_send
.
Returns pointer to the new environment.
void *enif_alloc_resource( | OTP R13B04 |
Allocates a memory-managed resource object of type type
and size size
bytes.
size_t enif_binary_to_term( | OTP 19.0 |
Creates a term that is the result of decoding the binary data at data
, which must be encoded according to the Erlang external term format. No more than size
bytes are read from data
. Argument opts
corresponds to the second argument to erlang:binary_to_term/2
and must be either 0
or ERL_NIF_BIN2TERM_SAFE
.
On success, stores the resulting term at *term
and returns the number of bytes read. Returns 0
if decoding fails or if opts
is invalid.
See also ErlNifBinaryToTerm
, erlang:binary_to_term/2
, and enif_term_to_binary
.
void enif_clear_env( | OTP R14B |
Frees all terms in an environment and clears it for reuse. The environment must have been allocated with enif_alloc_env
.
int enif_compare( | OTP R13B04 |
Returns an integer < 0
if lhs
< rhs
, 0
if lhs
= rhs
, and > 0
if lhs
> rhs
. Corresponds to the Erlang operators ==
, /=
, =<
, <
, >=
, and >
(but not =:=
or =/=
).
int enif_compare_monitors( | OTP 20.0 |
Compares two ErlNifMonitor
s. Can also be used to imply some artificial order on monitors, for whatever reason.
Returns 0
if monitor1
and monitor2
are equal, < 0
if monitor1
< monitor2
, and > 0
if monitor1
> monitor2
.
int enif_compare_pids( | OTP 22.0 |
Compares two ErlNifPid
s according to term order.
Returns 0
if pid1
and pid2
are equal, < 0
if pid1
< pid2
, and > 0
if pid1
> pid2
.
void enif_cond_broadcast( | OTP R13B04 |
Same as erl_drv_cond_broadcast
.
ErlNifCond * enif_cond_create( | OTP R13B04 |
Same as erl_drv_cond_create
.
void enif_cond_destroy( | OTP R13B04 |
Same as erl_drv_cond_destroy
.
char* enif_cond_name( | OTP 21.0 |
Same as erl_drv_cond_name
.
void enif_cond_signal( | OTP R13B04 |
Same as erl_drv_cond_signal
.
void enif_cond_wait( | OTP R13B04 |
Same as erl_drv_cond_wait
.
int enif_consume_timeslice( | OTP R16B |
Gives the runtime system a hint about how much CPU time the current NIF call has consumed since the last hint, or since the start of the NIF if no previous hint has been specified. The time is specified as a percent of the timeslice that a process is allowed to execute Erlang code until it can be suspended to give time for other runnable processes. The scheduling timeslice is not an exact entity, but can usually be approximated to about 1 millisecond.
Notice that it is up to the runtime system to determine if and how to use this information. Implementations on some platforms can use other means to determine consumed CPU time. Lengthy NIFs should regardless of this frequently call enif_consume_timeslice
to determine if it is allowed to continue execution.
Argument percent
must be an integer between 1 and 100. This function must only be called from a NIF-calling thread, and argument env
must be the environment of the calling process.
Returns 1
if the timeslice is exhausted, otherwise 0
. If 1
is returned, the NIF is to return as soon as possible in order for the process to yield.
This function is provided to better support co-operative scheduling, improve system responsiveness, and make it easier to prevent misbehaviors of the VM because of a NIF monopolizing a scheduler thread. It can be used to divide length work
into a number of repeated NIF calls without the need to create threads.
See also the warning
text at the beginning of this manual page.
ErlNifTime enif_convert_time_unit( | OTP 18.3 |
Converts the val
value of time unit from
to the corresponding value of time unit to
. The result is rounded using the floor function.
val
- Value to convert time unit for.
from
- Time unit of
val
. to
- Time unit of returned value.
Returns ERL_NIF_TIME_ERROR
if called with an invalid time unit argument.
See also ErlNifTime
and ErlNifTimeUnit
.
ERL_NIF_TERM enif_cpu_time( | OTP 19.0 |
Returns the CPU time in the same format as erlang:timestamp()
. The CPU time is the time the current logical CPU has spent executing since some arbitrary point in the past. If the OS does not support fetching this value, enif_cpu_time
invokes enif_make_badarg
.
int enif_demonitor_process( | OTP 20.0 |
Cancels a monitor created earlier with enif_monitor_process
. Argument obj
is a pointer to the resource holding the monitor and *mon
identifies the monitor.
Argument caller_env
is the environment of the calling thread (process bound
or callback
environment) or NULL
if calling from a custom thread not spawned by ERTS.
Returns 0
if the monitor was successfully identified and removed. Returns a non-zero value if the monitor could not be identified, which means it was either
- never created for this resource
- already cancelled
- already triggered
- just about to be triggered by a concurrent thread
This function is thread-safe.
int enif_dynamic_resource_call( | OTP 24.0 |
Call code of a resource type implemented by another NIF module. The atoms rt_module
and rt_name
identifies the resource type to be called. Argument resource
identifies a resource object of that type.
The callback dyncall
of the identified resource type will be called with a pointer to the resource objects obj
and the argument call_data
passed through. The call_data
argument is typically a pointer to a struct used to passed both arguments to the dyncall
function as well as results back to the caller.
Returns 0 if the dyncall
callback function was called. Returns a non-zero value if no call was made, which happens if rt_module
and rt_name
did not identify a resource type with a dyncall
callback or if resource
was not a resource object of that type.
int enif_equal_tids( | OTP R13B04 |
Same as erl_drv_equal_tids
.
int enif_fprintf( | OTP 21.0 |
Similar to fprintf
but this format string also accepts "%T"
, which formats Erlang terms of type ERL_NIF_TERM
.
This function is primarily intended for debugging purpose. It is not recommended to print very large terms with %T
. The function may change errno
, even if successful.
void enif_free( |
Frees memory allocated by enif_alloc
.
void enif_free_env( | OTP R14B |
Frees an environment allocated with enif_alloc_env
. All terms created in the environment are freed as well.
void enif_free_iovec( | OTP 20.1 |
Frees an io vector returned from enif_inspect_iovec
. This is needed only if a NULL
environment is passed to enif_inspect_iovec
.
ErlNifIOVec *iovec = NULL; size_t max_elements = 128; ERL_NIF_TERM tail; if (!enif_inspect_iovec(NULL, max_elements, term, &tail, &iovec)) return 0; // Do things with the iovec /* Free the iovector, possibly in another thread or nif function call */ enif_free_iovec(iovec);
int enif_get_atom( | OTP R13B04 |
Writes a NULL
-terminated string in the buffer pointed to by buf
of size size
, consisting of the string representation of the atom term
with encoding encode
.
Returns the number of bytes written (including terminating NULL
character) or 0
if term
is not an atom with maximum length of size-1
.
int enif_get_atom_length( | OTP R14B |
Sets *len
to the length (number of bytes excluding terminating NULL
character) of the atom term
with encoding encode
.
Returns true
on success, or false
if term
is not an atom.
int enif_get_double( | OTP R13B04 |
Sets *dp
to the floating-point value of term
.
Returns true
on success, or false
if term
is not a float.
int enif_get_int( |
Sets *ip
to the integer value of term
.
Returns true
on success, or false
if term
is not an integer or is outside the bounds of type int
.
int enif_get_int64( | OTP R14B |
Sets *ip
to the integer value of term
.
Returns true
on success, or false
if term
is not an integer or is outside the bounds of a signed 64-bit integer.
int enif_get_local_pid( | OTP R14B |
If term
is the pid of a node local process, this function initializes the pid variable *pid
from it and returns true
. Otherwise returns false
. No check is done to see if the process is alive.
enif_get_local_pid
will return false if argument term
is the atom undefined
.
int enif_get_local_port( | OTP 19.0 |
If term
identifies a node local port, this function initializes the port variable *port_id
from it and returns true
. Otherwise returns false
. No check is done to see if the port is alive.
int enif_get_list_cell( |
Sets *head
and *tail
from list list
.
Returns true
on success, or false
if it is not a list or the list is empty.
int enif_get_list_length( | OTP R14B |
Sets *len
to the length of list term
.
Returns true
on success, or false
if term
is not a proper list.
int enif_get_long( | OTP R13B04 |
Sets *ip
to the long integer value of term
.
Returns true
on success, or false
if term
is not an integer or is outside the bounds of type long int
.
int enif_get_map_size( | OTP 18.0 |
Sets *size
to the number of key-value pairs in the map term
.
Returns true
on success, or false
if term
is not a map.
int enif_get_map_value( | OTP 18.0 |
Sets *value
to the value associated with key
in the map map
.
Returns true
on success, or false
if map
is not a map or if map
does not contain key
.
int enif_get_resource( | OTP R13B04 |
Sets *objp
to point to the resource object referred to by term
.
Returns true
on success, or false
if term
is not a handle to a resource object of type type
.
enif_get_resource
does not add a reference to the resource object. However, the pointer received in *objp
is guaranteed to be valid at least as long as the resource handle term
is valid.
int enif_get_string( | OTP R13B04 |
Writes a NULL
-terminated string in the buffer pointed to by buf
with size size
, consisting of the characters in the string list
. The characters are written using encoding encode
.
Returns one of the following:
- The number of bytes written (including terminating
NULL
character) -
-size
if the string was truncated because of buffer space -
0
iflist
is not a string that can be encoded withencode
or ifsize
was <1
.
The written string is always NULL
-terminated, unless buffer size
is < 1
.
int enif_get_tuple( | OTP R13B04 |
If term
is a tuple, this function sets *array
to point to an array containing the elements of the tuple, and sets *arity
to the number of elements. Notice that the array is read-only and (*array)[N-1]
is the Nth element of the tuple. *array
is undefined if the arity of the tuple is zero.
Returns true
on success, or false
if term
is not a tuple.
int enif_get_uint( | OTP R13B04 |
Sets *ip
to the unsigned integer value of term
.
Returns true
on success, or false
if term
is not an unsigned integer or is outside the bounds of type unsigned int
.
int enif_get_uint64( | OTP R14B |
Sets *ip
to the unsigned integer value of term
.
Returns true
on success, or false
if term
is not an unsigned integer or is outside the bounds of an unsigned 64-bit integer.
int enif_get_ulong( |
Sets *ip
to the unsigned long integer value of term
.
Returns true
on success, or false
if term
is not an unsigned integer or is outside the bounds of type unsigned long
.
int enif_getenv( | OTP 18.2 |
Same as erl_drv_getenv
.
int enif_has_pending_exception( | OTP 18.0 |
Returns true
if a pending exception is associated with the environment env
. If reason
is a NULL
pointer, ignore it. Otherwise, if a pending exception associated with env
exists, set *reason
to the value of the exception term. For example, if enif_make_badarg
is called to set a pending badarg
exception, a later call to enif_has_pending_exception(env, &reason)
sets *reason
to the atom badarg
, then return true
.
See also enif_make_badarg
and enif_raise_exception
.
ErlNifUInt64 enif_hash( | OTP 20.0 |
Hashes term
according to the specified ErlNifHash
type
.
Ranges of taken salt (if any) and returned value depend on the hash type.
int enif_inspect_binary( |
Initializes the structure pointed to by bin
with information about binary term bin_term
.
Returns true
on success, or false
if bin_term
is not a binary.
int enif_inspect_iolist_as_binary( | OTP R13B04 |
Initializes the structure pointed to by bin
with a continuous buffer with the same byte content as iolist
. As with inspect_binary
, the data pointed to by bin
is transient and does not need to be released.
Returns true
on success, or false
if iolist
is not an iolist.
int enif_inspect_iovec( | OTP 20.1 |
Fills iovec
with the list of binaries provided in iovec_term
. The number of elements handled in the call is limited to max_elements
, and tail
is set to the remainder of the list. Note that the output may be longer than max_elements
on some platforms.
To create a list of binaries from an arbitrary iolist, use erlang:iolist_to_iovec/1
.
When calling this function, iovec
should contain a pointer to NULL
or a ErlNifIOVec structure that should be used if possible. e.g.
/* Don't use a pre-allocated structure */ ErlNifIOVec *iovec = NULL; enif_inspect_iovec(env, max_elements, term, &tail, &iovec); /* Use a stack-allocated vector as an optimization for vectors with few elements */ ErlNifIOVec vec, *iovec = &vec; enif_inspect_iovec(env, max_elements, term, &tail, &iovec);
The contents of the iovec
is valid until the called nif function returns. If the iovec
should be valid after the nif call returns, it is possible to call this function with a NULL
environment. If no environment is given the iovec
owns the data in the vector and it has to be explicitly freed using enif_free_iovec
.
Returns true
on success, or false
if iovec_term
not an iovec.
ErlNifIOQueue * enif_ioq_create( | OTP 20.1 |
Create a new I/O Queue that can be used to store data. opts
has to be set to ERL_NIF_IOQ_NORMAL
.
void enif_ioq_destroy( | OTP 20.1 |
Destroy the I/O queue and free all of it's contents
int enif_ioq_deq( | OTP 20.1 |
Dequeue count
bytes from the I/O queue. If size
is not NULL
, the new size of the queue is placed there.
Returns true
on success, or false
if the I/O does not contain count
bytes. On failure the queue is left un-altered.
int enif_ioq_enq_binary( | OTP 20.1 |
Enqueue the bin
into q
skipping the first skip
bytes.
Returns true
on success, or false
if skip
is greater than the size of bin
. Any ownership of the binary data is transferred to the queue and bin
is to be considered read-only for the rest of the NIF call and then as released.
int enif_ioq_enqv( | OTP 20.1 |
Enqueue the iovec
into q
skipping the first skip
bytes.
Returns true
on success, or false
if skip
is greater than the size of iovec
.
SysIOVec * enif_ioq_peek( | OTP 20.1 |
Get the I/O queue as a pointer to an array of SysIOVec
s. It also returns the number of elements in iovlen
.
Nothing is removed from the queue by this function, that must be done with enif_ioq_deq
.
The returned array is suitable to use with the Unix system call writev
.
int enif_ioq_peek_head( | OTP 21.0 |
Get the head of the IO Queue as a binary term.
If size
is not NULL
, the size of the head is placed there.
Nothing is removed from the queue by this function, that must be done with enif_ioq_deq
.
Returns true
on success, or false
if the queue is empty.
size_t enif_ioq_size( | OTP 20.1 |
Get the size of q
.
int enif_is_atom( | OTP R13B04 |
Returns true
if term
is an atom.
int enif_is_binary( |
Returns true
if term
is a binary.
int enif_is_current_process_alive( | OTP 19.0 |
Returns true
if the currently executing process is currently alive, otherwise false
.
This function can only be used from a NIF-calling thread, and with an environment corresponding to currently executing processes.
int enif_is_empty_list( | OTP R13B04 |
Returns true
if term
is an empty list.
int enif_is_exception( | OTP R14B03 |
Return true if term
is an exception.
int enif_is_fun( | OTP R13B04 |
Returns true
if term
is a fun.
int enif_is_identical( | OTP R13B04 |
Returns true
if the two terms are identical. Corresponds to the Erlang operators =:=
and =/=
.
int enif_is_list( | OTP R14B |
Returns true
if term
is a list.
int enif_is_map( | OTP 18.0 |
Returns true
if term
is a map, otherwise false
.
int enif_is_number( | OTP R15B |
Returns true
if term
is a number.
int enif_is_pid( | OTP R13B04 |
Returns true
if term
is a pid.
int enif_is_pid_undefined( | OTP 22.0 |
Returns true
if pid
has been set as undefined by enif_set_pid_undefined
.
int enif_is_port( | OTP R13B04 |
Returns true
if term
is a port.
int enif_is_port_alive( | OTP 19.0 |
Returns true
if port_id
is alive.
This function is thread-safe.
int enif_is_process_alive( | OTP 19.0 |
Returns true
if pid
is alive.
This function is thread-safe.
int enif_is_ref( | OTP R13B04 |
Returns true
if term
is a reference.
int enif_is_tuple( | OTP R14B |
Returns true
if term
is a tuple.
int enif_keep_resource( | OTP R14B |
Adds a reference to resource object obj
obtained from enif_alloc_resource
. Each call to enif_keep_resource
for an object must be balanced by a call to enif_release_resource
before the object is destructed.
ERL_NIF_TERM enif_make_atom( |
Creates an atom term from the NULL
-terminated C-string name
with ISO Latin-1 encoding. If the length of name
exceeds the maximum length allowed for an atom (255 characters), enif_make_atom
invokes enif_make_badarg
.
ERL_NIF_TERM enif_make_atom_len( | OTP R14B |
Create an atom term from the string name
with length len
. NULL
characters are treated as any other characters. If len
exceeds the maximum length allowed for an atom (255 characters), enif_make_atom
invokes enif_make_badarg
.
ERL_NIF_TERM enif_make_badarg( |
Makes a badarg
exception to be returned from a NIF, and associates it with environment env
. Once a NIF or any function it calls invokes enif_make_badarg
, the runtime ensures that a badarg
exception is raised when the NIF returns, even if the NIF attempts to return a non-exception term instead.
The return value from enif_make_badarg
can be used only as the return value from the NIF that invoked it (directly or indirectly) or be passed to enif_is_exception
, but not to any other NIF API function.
See also enif_has_pending_exception
and enif_raise_exception
.
Before ERTS 7.0 (Erlang/OTP 18), the return value from enif_make_badarg
had to be returned from the NIF. This requirement is now lifted as the return value from the NIF is ignored if enif_make_badarg
has been invoked.
ERL_NIF_TERM enif_make_binary( |
Makes a binary term from bin
. Any ownership of the binary data is transferred to the created term and bin
is to be considered read-only for the rest of the NIF call and then as released.
ERL_NIF_TERM enif_make_copy( | OTP R14B |
Makes a copy of term src_term
. The copy is created in environment dst_env
. The source term can be located in any environment.
ERL_NIF_TERM enif_make_double( | OTP R13B04 |
Creates a floating-point term from a double
. If argument double
is not finite or is NaN, enif_make_double
invokes enif_make_badarg
.
int enif_make_existing_atom( | OTP R13B04 |
Tries to create the term of an already existing atom from the NULL
-terminated C-string name
with encoding encode
.
If the atom already exists, this function stores the term in *atom
and returns true
, otherwise false
. Also returns false
if the length of name
exceeds the maximum length allowed for an atom (255 characters).
int enif_make_existing_atom_len( | OTP R14B |
Tries to create the term of an already existing atom from the string name
with length len
and encoding encode
. NULL
characters are treated as any other characters.
If the atom already exists, this function stores the term in *atom
and returns true
, otherwise false
. Also returns false
if len
exceeds the maximum length allowed for an atom (255 characters).
ERL_NIF_TERM enif_make_int( |
Creates an integer term.
ERL_NIF_TERM enif_make_int64( | OTP R14B |
Creates an integer term from a signed 64-bit integer.
ERL_NIF_TERM enif_make_list( |
Creates an ordinary list term of length cnt
. Expects cnt
number of arguments (after cnt
) of type ERL_NIF_TERM
as the elements of the list.
Returns an empty list if cnt
is 0.
ERL_NIF_TERM enif_make_list1( | OTP R13B04 |
ERL_NIF_TERM enif_make_list2( | OTP R13B04 |
ERL_NIF_TERM enif_make_list3( | OTP R13B04 |
ERL_NIF_TERM enif_make_list4( | OTP R13B04 |
ERL_NIF_TERM enif_make_list5( | OTP R13B04 |
ERL_NIF_TERM enif_make_list6( | OTP R13B04 |
ERL_NIF_TERM enif_make_list7( | OTP R13B04 |
ERL_NIF_TERM enif_make_list8( | OTP R13B04 |
ERL_NIF_TERM enif_make_list9( | OTP R13B04 |
Creates an ordinary list term with length indicated by the function name. Prefer these functions (macros) over the variadic enif_make_list
to get a compile-time error if the number of arguments does not match.
ERL_NIF_TERM enif_make_list_cell( |
Creates a list cell [head | tail]
.
ERL_NIF_TERM enif_make_list_from_array( | OTP R13B04 |
Creates an ordinary list containing the elements of array arr
of length cnt
.
Returns an empty list if cnt
is 0.
ERL_NIF_TERM enif_make_long( | OTP R13B04 |
Creates an integer term from a long int
.
int enif_make_map_put( | OTP 18.0 |
Makes a copy of map map_in
and inserts key
with value
. If key
already exists in map_in
, the old associated value is replaced by value
.
If successful, this function sets *map_out
to the new map and returns true
. Returns false
if map_in
is not a map.
The map_in
term must belong to environment env
.
int enif_make_map_remove( | OTP 18.0 |
If map map_in
contains key
, this function makes a copy of map_in
in *map_out
, and removes key
and the associated value. If map map_in
does not contain key
, *map_out
is set to map_in
.
Returns true
on success, or false
if map_in
is not a map.
The map_in
term must belong to environment env
.
int enif_make_map_update( | OTP 18.0 |
Makes a copy of map map_in
and replace the old associated value for key
with new_value
.
If successful, this function sets *map_out
to the new map and returns true
. Returns false
if map_in
is not a map or if it does not contain key
.
The map_in
term must belong to environment env
.
int enif_make_map_from_arrays( | OTP 21.0 |
Makes a map term from the given keys and values.
If successful, this function sets *map_out
to the new map and returns true
. Returns false
there are any duplicate keys.
All keys and values must belong to env
.
ERL_NIF_TERM enif_make_monitor_term( | OTP 22.0 |
Creates a term identifying the given monitor received from enif_monitor_process
.
This function is primarily intended for debugging purpose.
unsigned char *enif_make_new_binary( | OTP R14B |
Allocates a binary of size size
bytes and creates an owning term. The binary data is mutable until the calling NIF returns. This is a quick way to create a new binary without having to use ErlNifBinary
. The drawbacks are that the binary cannot be kept between NIF calls and it cannot be reallocated.
Returns a pointer to the raw binary data and sets *termp
to the binary term.
ERL_NIF_TERM enif_make_new_map( | OTP 18.0 |
Makes an empty map term.
ERL_NIF_TERM enif_make_pid( | OTP R14B |
Makes a pid term or the atom undefined
from *pid
.
ERL_NIF_TERM enif_make_ref( | OTP R13B04 |
Creates a reference like erlang:make_ref/0
.
ERL_NIF_TERM enif_make_resource( | OTP R13B04 |
Creates an opaque handle to a memory-managed resource object obtained by enif_alloc_resource
. No ownership transfer is done, as the resource object still needs to be released by enif_release_resource
. However, notice that the call to enif_release_resource
can occur immediately after obtaining the term from enif_make_resource
, in which case the resource object is deallocated when the term is garbage collected. For more details, see the example of creating and returning a resource object
in the User's Guide.
Since ERTS 9.0 (OTP-20.0), resource terms have a defined behavior when compared and serialized through term_to_binary
or passed between nodes.
-
Two resource terms will compare equal if and only if they would yield the same resource object pointer when passed to
enif_get_resource
. -
A resource term can be serialized with
term_to_binary
and later be fully recreated if the resource object is still alive whenbinary_to_term
is called. A stale resource term will be returned frombinary_to_term
if the resource object has been deallocated.enif_get_resource
will return false for stale resource terms.The same principles of serialization apply when passing resource terms in messages to remote nodes and back again. A resource term will act stale on all nodes except the node where its resource object is still alive in memory.
Before ERTS 9.0 (OTP-20.0), all resource terms did compare equal to each other and to empty binaries (<<>>
). If serialized, they would be recreated as plain empty binaries.
ERL_NIF_TERM enif_make_resource_binary( | OTP R14B |
Creates a binary term that is memory-managed by a resource object obj
obtained by enif_alloc_resource
. The returned binary term consists of size
bytes pointed to by data
. This raw binary data must be kept readable and unchanged until the destructor of the resource is called. The binary data can be stored external to the resource object, in which case the destructor is responsible for releasing the data.
Several binary terms can be managed by the same resource object. The destructor is not called until the last binary is garbage collected. This can be useful to return different parts of a larger binary buffer.
As with enif_make_resource
, no ownership transfer is done. The resource still needs to be released with enif_release_resource
.
int enif_make_reverse_list( | OTP R15B |
Sets *list_out
to the reverse list of the list list_in
and returns true
, or returns false
if list_in
is not a list.
This function is only to be used on short lists, as a copy is created of the list, which is not released until after the NIF returns.
The list_in
term must belong to environment env
.
ERL_NIF_TERM enif_make_string( |
Creates a list containing the characters of the NULL
-terminated string string
with encoding encoding
.
ERL_NIF_TERM enif_make_string_len( | OTP R14B |
Creates a list containing the characters of the string string
with length len
and encoding encoding
. NULL
characters are treated as any other characters.
ERL_NIF_TERM enif_make_sub_binary( | OTP R13B04 |
Makes a subbinary of binary bin_term
, starting at zero-based position pos
with a length of size
bytes. bin_term
must be a binary or bitstring. pos+size
must be less or equal to the number of whole bytes in bin_term
.
ERL_NIF_TERM enif_make_tuple( |
Creates a tuple term of arity cnt
. Expects cnt
number of arguments (after cnt
) of type ERL_NIF_TERM
as the elements of the tuple.
ERL_NIF_TERM enif_make_tuple1( | OTP R13B04 |
ERL_NIF_TERM enif_make_tuple2( | OTP R13B04 |
ERL_NIF_TERM enif_make_tuple3( | OTP R13B04 |
ERL_NIF_TERM enif_make_tuple4( | OTP R13B04 |
ERL_NIF_TERM enif_make_tuple5( | OTP R13B04 |
ERL_NIF_TERM enif_make_tuple6( | OTP R13B04 |
ERL_NIF_TERM enif_make_tuple7( | OTP R13B04 |
ERL_NIF_TERM enif_make_tuple8( | OTP R13B04 |
ERL_NIF_TERM enif_make_tuple9( | OTP R13B04 |
Creates a tuple term with length indicated by the function name. Prefer these functions (macros) over the variadic enif_make_tuple
to get a compile-time error if the number of arguments does not match.
ERL_NIF_TERM enif_make_tuple_from_array( | OTP R13B04 |
Creates a tuple containing the elements of array arr
of length cnt
.
ERL_NIF_TERM enif_make_uint( | OTP R13B04 |
Creates an integer term from an unsigned int
.
ERL_NIF_TERM enif_make_uint64( | OTP R14B |
Creates an integer term from an unsigned 64-bit integer.
ERL_NIF_TERM enif_make_ulong( |
Creates an integer term from an unsigned long int
.
ERL_NIF_TERM enif_make_unique_integer( | OTP 19.0 |
Returns a unique integer with the same properties as specified by erlang:unique_integer/1
.
env
is the environment to create the integer in.
ERL_NIF_UNIQUE_POSITIVE
and ERL_NIF_UNIQUE_MONOTONIC
can be passed as the second argument to change the properties of the integer returned. They can be combined by OR:ing the two values together.
See also ErlNifUniqueInteger
.
int enif_map_iterator_create( | OTP 18.0 |
Creates an iterator for the map map
by initializing the structure pointed to by iter
. Argument entry
determines the start position of the iterator: ERL_NIF_MAP_ITERATOR_FIRST
or ERL_NIF_MAP_ITERATOR_LAST
.
Returns true
on success, or false if map
is not a map.
A map iterator is only useful during the lifetime of environment env
that the map
belongs to. The iterator must be destroyed by calling enif_map_iterator_destroy
:
ERL_NIF_TERM key, value; ErlNifMapIterator iter; enif_map_iterator_create(env, my_map, &iter, ERL_NIF_MAP_ITERATOR_FIRST); while (enif_map_iterator_get_pair(env, &iter, &key, &value)) { do_something(key,value); enif_map_iterator_next(env, &iter); } enif_map_iterator_destroy(env, &iter);
The key-value pairs of a map have no defined iteration order. The only guarantee is that the iteration order of a single map instance is preserved during the lifetime of the environment that the map belongs to.
void enif_map_iterator_destroy( | OTP 18.0 |
Destroys a map iterator created by enif_map_iterator_create
.
int enif_map_iterator_get_pair( | OTP 18.0 |
Gets key and value terms at the current map iterator position.
On success, sets *key
and *value
and returns true
. Returns false
if the iterator is positioned at head (before first entry) or tail (beyond last entry).
int enif_map_iterator_is_head( | OTP 18.0 |
Returns true
if map iterator iter
is positioned before the first entry.
int enif_map_iterator_is_tail( | OTP 18.0 |
Returns true
if map iterator iter
is positioned after the last entry.
int enif_map_iterator_next( | OTP 18.0 |
Increments map iterator to point to the next key-value entry.
Returns true
if the iterator is now positioned at a valid key-value entry, or false
if the iterator is positioned at the tail (beyond the last entry).
int enif_map_iterator_prev( | OTP 18.0 |
Decrements map iterator to point to the previous key-value entry.
Returns true
if the iterator is now positioned at a valid key-value entry, or false
if the iterator is positioned at the head (before the first entry).
int enif_monitor_process( | OTP 20.0 |
Starts monitoring a process from a resource. When a process is monitored, a process exit results in a call to the provided down
callback associated with the resource type.
Argument obj
is pointer to the resource to hold the monitor and *target_pid
identifies the local process to be monitored.
If mon
is not NULL
, a successful call stores the identity of the monitor in the ErlNifMonitor
struct pointed to by mon
. This identifier is used to refer to the monitor for later removal with enif_demonitor_process
or compare with enif_compare_monitors
. A monitor is automatically removed when it triggers or when the resource is deallocated.
Argument caller_env
is the environment of the calling thread (process bound
or callback
environment) or NULL
if calling from a custom thread not spawned by ERTS.
Returns 0
on success, < 0 if no down
callback is provided, and > 0 if the process is no longer alive or if target_pid
is undefined
.
This function is thread-safe.
ErlNifTime enif_monotonic_time( | OTP 18.3 |
Returns the current Erlang monotonic time
. Notice that it is not uncommon with negative values.
time_unit
is the time unit of the returned value.
Returns ERL_NIF_TIME_ERROR
if called with an invalid time unit argument, or if called from a thread that is not a scheduler thread.
See also ErlNifTime
and ErlNifTimeUnit
.
ErlNifMutex * enif_mutex_create( | OTP R13B04 |
Same as erl_drv_mutex_create
.
void enif_mutex_destroy( | OTP R13B04 |
Same as erl_drv_mutex_destroy
.
void enif_mutex_lock( | OTP R13B04 |
Same as erl_drv_mutex_lock
.
char* enif_mutex_name( | OTP 21.0 |
Same as erl_drv_mutex_name
.
int enif_mutex_trylock( | OTP R13B04 |
Same as erl_drv_mutex_trylock
.
void enif_mutex_unlock( | OTP R13B04 |
Same as erl_drv_mutex_unlock
.
ERL_NIF_TERM enif_now_time( | OTP 19.0 |
Returns an erlang:now()
time stamp.
This function is deprecated.
ErlNifResourceType * enif_open_resource_type( | OTP R13B04 |
Creates or takes over a resource type identified by the string name
and gives it the destructor function pointed to by dtor
. Argument flags
can have the following values:
ERL_NIF_RT_CREATE
- Creates a new resource type that does not already exist.
ERL_NIF_RT_TAKEOVER
- Opens an existing resource type and takes over ownership of all its instances. The supplied destructor
dtor
is called both for existing instances and new instances not yet created by the calling NIF library.
The two flag values can be combined with bitwise OR. The resource type name is local to the calling module. Argument module_str
is not (yet) used and must be NULL
. dtor
can be NULL
if no destructor is needed.
On success, the function returns a pointer to the resource type and *tried
is set to either ERL_NIF_RT_CREATE
or ERL_NIF_RT_TAKEOVER
to indicate what was done. On failure, returns NULL
and sets *tried
to flags
. It is allowed to set tried
to NULL
.
Notice that enif_open_resource_type
is only allowed to be called in the two callbacks load
and upgrade
.
See also enif_open_resource_type_x
.
ErlNifResourceType * enif_open_resource_type_x( | OTP 20.0 |
Same as enif_open_resource_type
except it accepts additional callback functions for resource types that are used together with enif_select
and enif_monitor_process
.
Argument init
is a pointer to an ErlNifResourceTypeInit
structure that contains the function pointers for destructor, down and stop callbacks for the resource type.
Only members dtor
, down
and stop
in ErlNifResourceTypeInit
are read by enif_open_resource_type_x
. To implement the new dyncall
callback use enif_init_resource_type
.
ErlNifResourceType * enif_init_resource_type( | OTP 24.0 |
Same as enif_open_resource_type_x
except it accepts an additional callback function for resource types that are used together with enif_dynamic_resource_call
.
Argument init
is a pointer to an ErlNifResourceTypeInit
structure that contains the callback function pointers dtor
, down
, stop
and the new dyncall
. The struct also contains the field members
that must be set to the number of initialized callbacks counted from the top of the struct. For example, to initialize all callbacks including dyncall
, members
should be set to 4. All callbacks are optional and may be set to NULL
.
int enif_port_command( | OTP 19.0 |
Works as erlang:port_command/2
, except that it is always completely asynchronous.
env
- The environment of the calling process. Must not be
NULL
. *to_port
- The port ID of the receiving port. The port ID is to refer to a port on the local node.
msg_env
- The environment of the message term. Can be a process independent environment allocated with
enif_alloc_env
orNULL
. msg
- The message term to send. The same limitations apply as on the payload to
erlang:port_command/2
.
Using a msg_env
of NULL
is an optimization, which groups together calls to enif_alloc_env
, enif_make_copy
, enif_port_command
, and enif_free_env
into one call. This optimization is only useful when a majority of the terms are to be copied from env
to msg_env
.
Returns true
if the command is successfully sent. Returns false
if the command fails, for example:
-
*to_port
does not refer to a local port. - The currently executing process (that is, the sender) is not alive.
-
msg
is invalid.
See also enif_get_local_port
.
void * enif_priv_data( | OTP R13B04 |
ERL_NIF_TERM enif_raise_exception( | OTP 18.0 |
Creates an error exception with the term reason
to be returned from a NIF, and associates it with environment env
. Once a NIF or any function it calls invokes enif_raise_exception
, the runtime ensures that the exception it creates is raised when the NIF returns, even if the NIF attempts to return a non-exception term instead.
The return value from enif_raise_exception
can only be used as the return value from the NIF that invoked it (directly or indirectly) or be passed to enif_is_exception
, but not to any other NIF API function.
See also enif_has_pending_exception
and enif_make_badarg
.
void * enif_realloc( | OTP 20.2 |
Reallocates memory allocated by enif_alloc
to size
bytes.
Returns NULL
if the reallocation fails.
The returned pointer is suitably aligned for any built-in type that fit in the allocated memory.
int enif_realloc_binary( | OTP R13B04 |
Changes the size of a binary bin
. The source binary can be read-only, in which case it is left untouched and a mutable copy is allocated and assigned to *bin
.
Returns true
on success, or false
if memory allocation failed.
void enif_release_binary( |
Releases a binary obtained from enif_alloc_binary
.
void enif_release_resource( | OTP R13B04 |
Removes a reference to resource object obj
obtained from enif_alloc_resource
. The resource object is destructed when the last reference is removed. Each call to enif_release_resource
must correspond to a previous call to enif_alloc_resource
or enif_keep_resource
. References made by enif_make_resource
can only be removed by the garbage collector.
There are no guarantees exactly when the destructor of an unreferenced resource is called. It could be called directly by enif_release_resource
but it could also be scheduled to be called at a later time possibly by another thread.
ErlNifRWLock * enif_rwlock_create( | OTP R13B04 |
Same as erl_drv_rwlock_create
.
void enif_rwlock_destroy( | OTP R13B04 |
Same as erl_drv_rwlock_destroy
.
char* enif_rwlock_name( | OTP 21.0 |
Same as erl_drv_rwlock_name
.
void enif_rwlock_rlock( | OTP R13B04 |
Same as erl_drv_rwlock_rlock
.
void enif_rwlock_runlock( | OTP R13B04 |
Same as erl_drv_rwlock_runlock
.
void enif_rwlock_rwlock( | OTP R13B04 |
Same as erl_drv_rwlock_rwlock
.
void enif_rwlock_rwunlock( | OTP R13B04 |
Same as erl_drv_rwlock_rwunlock
.
int enif_rwlock_tryrlock( | OTP R13B04 |
Same as erl_drv_rwlock_tryrlock
.
int enif_rwlock_tryrwlock( | OTP R13B04 |
Same as erl_drv_rwlock_tryrwlock
.
ERL_NIF_TERM enif_schedule_nif( | OTP 17.3 |
Schedules NIF fp
to execute. This function allows an application to break up long-running work into multiple regular NIF calls or to schedule a dirty NIF
to execute on a dirty scheduler thread.
caller_env
-
Must be
process bound
environment of the calling NIF. fun_name
-
Provides a name for the NIF that is scheduled for execution. If it cannot be converted to an atom,
enif_schedule_nif
returns abadarg
exception. flags
-
Must be set to
0
for a regular NIF. If the emulator was built with dirty scheduler support enabled,flags
can be set to eitherERL_NIF_DIRTY_JOB_CPU_BOUND
if the job is expected to be CPU-bound, orERL_NIF_DIRTY_JOB_IO_BOUND
for jobs that will be I/O-bound. If dirty scheduler threads are not available in the emulator, an attempt to schedule such a job results in anotsup
exception. argc
andargv
-
Can either be the originals passed into the calling NIF, or can be values created by the calling NIF.
The calling NIF must use the return value of enif_schedule_nif
as its own return value.
Be aware that enif_schedule_nif
, as its name implies, only schedules the NIF for future execution. The calling NIF does not block waiting for the scheduled NIF to execute and return. This means that the calling NIF cannot expect to receive the scheduled NIF return value and use it for further operations.
int enif_select( | OTP 20.0 |
This function can be used to receive asynchronous notifications when OS-specific event objects become ready for either read or write operations.
Argument event
identifies the event object. On Unix systems, the functions select
/poll
are used. The event object must be a socket, pipe or other file descriptor object that select
/poll
can use.
Argument mode
describes the type of events to wait for. It can be ERL_NIF_SELECT_READ
, ERL_NIF_SELECT_WRITE
or a bitwise OR combination to wait for both. It can also be ERL_NIF_SELECT_STOP
or ERL_NIF_SELECT_CANCEL
which are described further below. When a read or write event is triggered, a notification message like this is sent to the process identified by pid
:
{select, Obj, Ref, ready_input | ready_output}
ready_input
or ready_output
indicates if the event object is ready for reading or writing.
For complete control over the message format use the newer functions enif_select_read
or enif_select_write
introduced in erts-11.0 (OTP-22.0).
Argument pid
may be NULL
to indicate the calling process. It must not be set as undefined
.
Argument obj
is a resource object obtained from enif_alloc_resource
. The purpose of the resource objects is as a container of the event object to manage its state and lifetime. A handle to the resource is received in the notification message as Obj
.
Argument ref
must be either a reference obtained from erlang:make_ref/0
or the atom undefined
. It will be passed as Ref
in the notifications. If a selective receive
statement is used to wait for the notification then a reference created just before the receive
will exploit a runtime optimization that bypasses all earlier received messages in the queue.
The notifications are one-shot only. To receive further notifications of the same type (read or write), repeated calls to enif_select
must be made after receiving each notification.
ERL_NIF_SELECT_CANCEL
can be used to cancel previously selected events. It must be used in a bitwise OR combination with ERL_NIF_SELECT_READ
and/or ERL_NIF_SELECT_WRITE
to indicate which type of event to cancel. Arguments pid
and ref
are ignored when ERL_NIF_SELECT_CANCEL
is specified. The return value will tell if the event was actualy cancelled or if a notification may already have been sent.
Use ERL_NIF_SELECT_STOP
as mode
in order to safely close an event object that has been passed to enif_select
. The stop
callback of the resource obj
will be called when it is safe to close the event object. This safe way of closing event objects must be used even if all notifications have been received (or cancelled) and no further calls to enif_select
have been made. ERL_NIF_SELECT_STOP
will first cancel any selected events before it calls or schedules the stop
callback. Arguments pid
and ref
are ignored when ERL_NIF_SELECT_STOP
is specified.
The first call to enif_select
for a specific OS event
will establish a relation between the event object and the containing resource. All subsequent calls for an event
must pass its containing resource as argument obj
. The relation is dissolved when enif_select
has been called with mode
as ERL_NIF_SELECT_STOP
and the corresponding stop
callback has returned. A resource can contain several event objects but one event object can only be contained within one resource. A resource will not be destructed until all its contained relations have been dissolved.
Use enif_monitor_process
together with enif_select
to detect failing Erlang processes and prevent them from causing permanent leakage of resources and their contained OS event objects.
Returns a non-negative value on success where the following bits can be set:
ERL_NIF_SELECT_STOP_CALLED
- The stop callback was called directly by
enif_select
. ERL_NIF_SELECT_STOP_SCHEDULED
- The stop callback was scheduled to run on some other thread or later by this thread.
ERL_NIF_SELECT_READ_CANCELLED
- A read event was cancelled by
ERL_NIF_SELECT_CANCEL
orERL_NIF_SELECT_STOP
and is guaranteed not to generate aready_input
notification message. ERL_NIF_SELECT_WRITE_CANCELLED
- A write event was cancelled by
ERL_NIF_SELECT_CANCEL
orERL_NIF_SELECT_STOP
and is guaranteed not to generate aready_output
notification message.
Returns a negative value if the call failed where the following bits can be set:
ERL_NIF_SELECT_INVALID_EVENT
- Argument
event
is not a valid OS event object. ERL_NIF_SELECT_FAILED
- The system call failed to add the event object to the poll set.
Use bitwise AND to test for specific bits in the return value. New significant bits may be added in future releases to give more detailed information for both failed and successful calls. Do NOT use equality tests like ==
, as that may cause your application to stop working.
Example:
retval = enif_select(env, fd, ERL_NIF_SELECT_STOP, resource, ref); if (retval < 0) { /* handle error */ } /* Success! */ if (retval & ERL_NIF_SELECT_STOP_CALLED) { /* ... */ }
The mode flag ERL_NIF_SELECT_CANCEL
and the return flags ERL_NIF_SELECT_READ_CANCELLED
and ERL_NIF_SELECT_WRITE_CANCELLED
were introduced in erts-11.0 (OTP-22.0).
int enif_select_read( | OTP 22.0 |
int enif_select_write( | OTP 22.0 |
These are variants of enif_select
where you can supply your own message term msg
that will be sent to the process instead of the predefined tuple {select,_,_,_}.
Argument msg_env
must either be NULL
or the environment of msg
allocated with enif_alloc_env
. If argument msg_env
is NULL
the term msg
will be copied, otherwise both msg
and msg_env
will be invalidated by a successful call to enif_select_read
or enif_select_write
. The environment is then to either be freed with enif_free_env
or cleared for reuse with enif_clear_env
. An unsuccessful call will leave msg
and msg_env
still valid.
Apart from the message format enif_select_read
and enif_select_write
behaves exactly the same as enif_select
with argument mode
as either ERL_NIF_SELECT_READ
or ERL_NIF_SELECT_WRITE
. To cancel or close events use enif_select
.
ErlNifPid * enif_self( | OTP R14B |
Initializes the ErlNifPid
variable at *pid
to represent the calling process.
Returns pid
if successful, or NULL if caller_env
is not a process bound environment
.
int enif_send( | OTP R14B |
Sends a message to a process.
caller_env
- The environment of the calling thread (
process bound
orcallback
environment) orNULL
if calling from a custom thread not spawned by ERTS. *to_pid
- The pid of the receiving process. The pid is to refer to a process on the local node.
msg_env
- The environment of the message term. Must be a process independent environment allocated with
enif_alloc_env
or NULL. msg
- The message term to send.
Returns true
if the message is successfully sent. Returns false
if the send operation fails, that is:
-
*to_pid
does not refer to an alive local process. - The currently executing process (that is, the sender) is not alive.
The message environment msg_env
with all its terms (including msg
) is invalidated by a successful call to enif_send
. The environment is to either be freed with enif_free_env
or cleared for reuse with enif_clear_env
. An unsuccessful call will leave msg
and msg_env
still valid.
If msg_env
is set to NULL
, the msg
term is copied and the original term and its environment is still valid after the call.
This function is thread-safe.
Passing msg_env
as NULL
is only supported as from ERTS 8.0 (Erlang/OTP 19).
void enif_set_pid_undefined( | OTP 22.0 |
Sets an ErlNifPid
variable as undefined. See enif_is_pid_undefined
.
unsigned enif_sizeof_resource( | OTP R13B04 |
Gets the byte size of resource object obj
obtained by enif_alloc_resource
.
int enif_snprintf( | OTP 19.0 |
Similar to snprintf
but this format string also accepts "%T"
, which formats Erlang terms of type ERL_NIF_TERM
.
This function is primarily intended for debugging purpose. It is not recommended to print very large terms with %T
. The function may change errno
, even if successful.
void enif_system_info( | OTP R13B04 |
Same as driver_system_info
.
int enif_term_to_binary( | OTP 19.0 |
Allocates a new binary with enif_alloc_binary
and stores the result of encoding term
according to the Erlang external term format.
Returns true
on success, or false
if the allocation fails.
See also erlang:term_to_binary/1
and enif_binary_to_term
.
ErlNifTermType enif_term_type( | OTP 22.0 |
Determines the type of the given term. The term must be an ordinary Erlang term and not one of the special terms returned by enif_raise_exception
, enif_schedule_nif
, or similar.
The following types are defined at the moment:
ERL_NIF_TERM_TYPE_ATOM
ERL_NIF_TERM_TYPE_BITSTRING
A bitstring or binary
ERL_NIF_TERM_TYPE_FLOAT
ERL_NIF_TERM_TYPE_FUN
ERL_NIF_TERM_TYPE_INTEGER
ERL_NIF_TERM_TYPE_LIST
A list, empty or not
ERL_NIF_TERM_TYPE_MAP
ERL_NIF_TERM_TYPE_PID
ERL_NIF_TERM_TYPE_PORT
ERL_NIF_TERM_TYPE_REFERENCE
ERL_NIF_TERM_TYPE_TUPLE
Note that new types may be added in the future, so the caller must be prepared to handle unknown types.
int enif_thread_create( | OTP R13B04 |
Same as erl_drv_thread_create
.
void enif_thread_exit( | OTP R13B04 |
Same as erl_drv_thread_exit
.
int enif_thread_join( | OTP R13B04 |
Same as erl_drv_thread_join
.
char* enif_thread_name( | OTP 21.0 |
Same as erl_drv_thread_name
.
ErlNifThreadOpts * enif_thread_opts_create( | OTP R13B04 |
Same as erl_drv_thread_opts_create
.
void enif_thread_opts_destroy( | OTP R13B04 |
Same as erl_drv_thread_opts_destroy
.
ErlNifTid enif_thread_self(void) | OTP R13B04 |
Same as erl_drv_thread_self
.
int enif_thread_type(void) | OTP 19.0 |
Determine the type of currently executing thread. A positive value indicates a scheduler thread while a negative value or zero indicates another type of thread. Currently the following specific types exist (which may be extended in the future):
ERL_NIF_THR_UNDEFINED
Undefined thread that is not a scheduler thread.
ERL_NIF_THR_NORMAL_SCHEDULER
A normal scheduler thread.
ERL_NIF_THR_DIRTY_CPU_SCHEDULER
A dirty CPU scheduler thread.
ERL_NIF_THR_DIRTY_IO_SCHEDULER
A dirty I/O scheduler thread.
ErlNifTime enif_time_offset( | OTP 18.3 |
Returns the current time offset between Erlang monotonic time
and Erlang system time
converted into the time_unit
passed as argument.
time_unit
is the time unit of the returned value.
Returns ERL_NIF_TIME_ERROR
if called with an invalid time unit argument or if called from a thread that is not a scheduler thread.
See also ErlNifTime
and ErlNifTimeUnit
.
void * enif_tsd_get( | OTP R13B04 |
Same as erl_drv_tsd_get
.
int enif_tsd_key_create( | OTP R13B04 |
Same as erl_drv_tsd_key_create
.
void enif_tsd_key_destroy( | OTP R13B04 |
Same as erl_drv_tsd_key_destroy
.
void enif_tsd_set( | OTP R13B04 |
Same as erl_drv_tsd_set
.
int enif_vfprintf( | OTP 21.0 |
Equivalent to enif_fprintf
except that its called with a va_list
instead of a variable number of arguments.
int enif_vsnprintf( | OTP 21.0 |
Equivalent to enif_snprintf
except that its called with a va_list
instead of a variable number of arguments.
int enif_whereis_pid( | OTP 20.0 |
Looks up a process by its registered name.
caller_env
- The environment of the calling thread (
process bound
orcallback
environment) orNULL
if calling from a custom thread not spawned by ERTS. name
- The name of a registered process, as an atom.
*pid
- The
ErlNifPid
in which the resolved process id is stored.
On success, sets *pid
to the local process registered with name
and returns true
. If name
is not a registered process, or is not an atom, false
is returned and *pid
is unchanged.
Works as erlang:whereis/1
, but restricted to processes. See enif_whereis_port
to resolve registered ports.
int enif_whereis_port( | OTP 20.0 |
Looks up a port by its registered name.
caller_env
- The environment of the calling thread (
process bound
orcallback
environment) orNULL
if calling from a custom thread not spawned by ERTS. name
- The name of a registered port, as an atom.
*port
- The
ErlNifPort
in which the resolved port id is stored.
On success, sets *port
to the port registered with name
and returns true
. If name
is not a registered port, or is not an atom, false
is returned and *port
is unchanged.
Works as erlang:whereis/1
, but restricted to ports. See enif_whereis_pid
to resolve registered processes.
See Also
© 2010–2021 Ericsson AB
Licensed under the Apache License, Version 2.0.