threadpool

Implements Nim's spawn.

See also:

Unstable API.

Imports

cpuinfo, cpuload, locks, os

Types

FlowVarBase = ref FlowVarBaseObj: Untyped base class for FlowVar[T]. Source Edit
FlowVar[T] {...}{.compilerProc.} = ref FlowVarObj[T]: A data flow variable. Source Edit
ThreadId = range[0 .. MaxDistinguishedThread - 1]: Source Edit

Consts

MaxThreadPoolSize = 256: Maximum size of the thread pool. 256 threads should be good enough for anybody ;-) Source Edit
MaxDistinguishedThread = 32: Maximum number of "distinguished" threads. Source Edit

Procs

proc blockUntil(fv: var FlowVarBaseObj) {...}{.raises: [], tags: [].}

Waits until the value for the fv arrives.

Usually it is not necessary to call this explicitly.

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proc awaitAndThen[T](fv: FlowVar[T]; action: proc (x: T) {...}{.closure.})

Blocks until the fv is available and then passes its value to action.

Note that due to Nim's parameter passing semantics this means that T doesn't need to be copied so awaitAndThen can sometimes be more efficient than ^ proc.

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proc unsafeRead[T](fv: FlowVar[ref T]): ptr T

Blocks until the value is available and then returns this value. Source Edit

proc `^`[T](fv: FlowVar[T]): T

Blocks until the value is available and then returns this value. Source Edit

proc blockUntilAny(flowVars: openArray[FlowVarBase]): int {...}{.raises: [], tags: [].}

Awaits any of the given flowVars. Returns the index of one flowVar for which a value arrived.

A flowVar only supports one call to blockUntilAny at the same time. That means if you blockUntilAny([a,b]) and blockUntilAny([b,c]) the second call will only block until c. If there is no flowVar left to be able to wait on, -1 is returned.

Note: This results in non-deterministic behaviour and should be avoided.

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proc isReady(fv: FlowVarBase): bool {...}{.raises: [], tags: [].}

Determines whether the specified FlowVarBase's value is available.

If true, awaiting fv will not block.

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proc setMinPoolSize(size: range[1 .. MaxThreadPoolSize]) {...}{.raises: [], tags: [].}

Sets the minimum thread pool size. The default value of this is 4. Source Edit

proc setMaxPoolSize(size: range[1 .. MaxThreadPoolSize]) {...}{.raises: [], tags: [].}

Sets the maximum thread pool size. The default value of this is MaxThreadPoolSize (256). Source Edit

proc preferSpawn(): bool {...}{.raises: [], tags: [].}

Use this proc to determine quickly if a spawn or a direct call is preferable.

If it returns true, a spawn may make sense. In general it is not necessary to call this directly; use spawnX template instead.

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proc spawn(call: sink typed): void {...}{.magic: "Spawn".}

Always spawns a new task, so that the call is never executed on the calling thread.

call has to be proc call p(...) where p is gcsafe and has a return type that is either void or compatible with FlowVar[T].

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proc pinnedSpawn(id: ThreadId; call: sink typed): void {...}{.magic: "Spawn".}

Always spawns a new task on the worker thread with id, so that the call is always executed on the thread.

call has to be proc call p(...) where p is gcsafe and has a return type that is either void or compatible with FlowVar[T].

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proc parallel(body: untyped) {...}{.magic: "Parallel".}

A parallel section can be used to execute a block in parallel.

body has to be in a DSL that is a particular subset of the language.

Please refer to the manual for further information.

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proc sync() {...}{.raises: [], tags: [TimeEffect].}

A simple barrier to wait for all spawn'ed tasks.

If you need more elaborate waiting, you have to use an explicit barrier.

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Templates

template spawnX(call)

Spawns a new task if a CPU core is ready, otherwise executes the call in the calling thread.

Usually it is advised to use spawn proc in order to not block the producer for an unknown amount of time.

call has to be proc call p(...) where p is gcsafe and has a return type that is either 'void' or compatible with FlowVar[T].

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