Interface VirtualMachineManager

public interface VirtualMachineManager

A manager of connections to target virtual machines. The VirtualMachineManager allows one application to debug multiple target VMs. (Note that the converse is not supported; a target VM can be debugged by only one debugger application.) This interface contains methods to manage connections to remote target VMs and to obtain the VirtualMachine mirror for available target VMs.

Connections can be made using one of several different Connector objects. Each connector encapsulates a different way of connecting the debugger with a target VM.

The VirtualMachineManager supports many different scenarios for connecting a debugger to a virtual machine. Four examples are presented in the table below. The examples use the command line syntax in Sun's implementation. Some Connector implementations may require slightly different handling than presented below.

Four scenarios for connecting a debugger to a virtual machine"

Scenario	Description
Debugger launches target VM (simplest, most-common scenario)	Debugger calls the LaunchingConnector.launch(java.util.Map) method of the default connector, obtained with defaultConnector(). The target VM is launched, and a connection between that VM and the debugger is established. A VirtualMachine mirror is returned. Or, for more control Debugger selects a connector from the list returned by launchingConnectors() with desired characteristics (for example, transport type, etc.). Debugger calls the LaunchingConnector.launch(java.util.Map) method of the selected connector. The target VM is launched, and a connection between that VM and the debugger is established. A VirtualMachine mirror is returned.
Debugger attaches to previously-running VM	Target VM is launched using the options -agentlib:jdwp=transport=xxx,server=y Target VM generates and outputs the tranport-specific address at which it will listen for a connection. Debugger is launched. Debugger selects a connector in the list returned by attachingConnectors() matching the transport with the name "xxx". Debugger presents the default connector parameters (obtained through Connector.defaultArguments()) to the end user, allowing the user to fill in the transport-specific address generated by the target VM. Debugger calls the AttachingConnector.attach(java.util.Map) method of the selected to attach to the target VM. A VirtualMachine mirror is returned.
Target VM attaches to previously-running debugger	At startup, debugger selects one or more connectors from the list returned by listeningConnectors() for one or more transports. Debugger calls the ListeningConnector.startListening(java.util.Map) method for each selected connector. For each call, a transport-specific address string is generated and returned. The debugger makes the transport names and corresponding address strings available to the end user. Debugger calls ListeningConnector.accept(java.util.Map) for each selected connector to wait for a target VM to connect. Later, target VM is launched by end user with the options -agentlib:jdwp=transport=xxx,address=yyy where "xxx" the transport for one of the connectors selected by the the debugger and "yyy" is the address generated by ListeningConnector.accept(java.util.Map) for that transport. Debugger's call to ListeningConnector.accept(java.util.Map) returns a VirtualMachine mirror.
Target VM launches debugger (sometimes called "Just-In-Time" debugging)	Target VM is launched with the options -agentlib:jdwp=launch=cmdline,onuncaught=y,transport=xxx,server=y Later, an uncaught exception is thrown in the target VM. The target VM generates the tranport-specific address at which it will listen for a connection. Target VM launches the debugger with the following items concatenated together (separated by spaces) to form the command line: The launch= value The transport= value The generated transport-specific address at which VM is listening for debugger connection. Upon launch, debugger selects a connector in the list returned by attachingConnectors() matching the transport with the name "xxx". Debugger changes the default connector parameters (obtained through Connector.defaultArguments()) to specify the transport specific address at which the VM is listenig. Optionally, other connector arguments can be presented to the user. Debugger calls the AttachingConnector.attach(java.util.Map) method of the selected to attach to the target VM. A VirtualMachine mirror is returned.

Connectors are created at start-up time. That is, they are created the first time that Bootstrap.virtualMachineManager() is invoked. The list of all Connectors created at start-up time can be obtained from the VirtualMachineManager by invoking the allConnectors method.

Connectors are created at start-up time if they are installed on the platform. In addition, Connectors are created automatically by the VirtualMachineManager to encapsulate any TransportService implementations that are installed on the platform. These two mechanisms for creating Connectors are described here.

A Connector is installed on the platform if it is installed in a jar file that is visible to the defining class loader of the Connector type, and that jar file contains a provider configuration file named Connector in the resource directory META-INF/services, and the provider configuration file lists the full-qualified class name of the Connector implementation. A Connector is a class that implements the Connector interface. More appropriately the class implements one of the specific Connector types, namely AttachingConnector, ListeningConnector, or LaunchingConnector. The format of the provider configuration file is one fully-qualified class name per line. Space and tab characters surrounding each class, as well as blank lines are ignored. The comment character is '#' (0x23), and on each line all characters following the first comment character are ignored. The file must be encoded in UTF-8.

At start-up time the VirtualMachineManager attempts to load and instantiate (using the no-arg constructor) each class listed in the provider configuration file. Exceptions thrown when loading or creating the Connector are caught and ignored. In other words, the start-up process continues despite of errors.

In addition to Connectors installed on the platform the VirtualMachineManager will also create Connectors to encapsulate any TransportService implementations that are installed on the platform. A TransportService is installed on the platform if it installed in a jar file that is visible to the defining class loader for the TransportService type, and that jar file contains a provider configuration file named TransportService in the resource directory META-INF/services, and the provider configuration file lists the full-qualified class name of the TransportService implementation. A TransportService is a concrete sub-class of TransportService. The format of the provider configuration file is the same as the provider configuration file for Connectors except that each class listed must be the fully-qualified class name of a class that implements the TransportService interface.

For each TransportService installed on the platform, the VirtualMachineManager creates a corresponding AttachingConnector and ListeningConnector. These Connectors are created to encapsulate a Transport that in turn encapsulates the TransportService. The AttachingConnector will be named based on the name of the transport service concatenated with the string Attach. For example, if the transport service name() method returns telepathic then the AttachingConnector will be named telepathicAttach. Similiarly the ListeningConnector will be named with the string Listen tagged onto the name of the transport service. The description() method of both the AttachingConnector, and the ListeningConnector, will delegate to the description() method of the underlying transport service. Both the AttachingConnector and the ListeningConnector will have two Connector Arguments. A StringArgument named address is the connector argument to specify the address to attach too, or to listen on. A IntegerArgument named timeout is the connector argument to specify the timeout when attaching, or accepting. The timeout connector may be ignored depending on if the transport service supports an attach timeout or accept timeout.

Initialization of the virtual machine manager will fail, that is Bootstrap.virtualMachineManager() will throw an error if the virtual machine manager is unable to create any connectors.