org.tanukisoftware.wrapper

Class WrapperActionServer

java.lang.Object

org.tanukisoftware.wrapper.WrapperActionServer

All Implemented Interfaces:

java.lang.Runnable

public class WrapperActionServer
extends java.lang.Object
implements java.lang.Runnable

If an application instantiates an instance of this class, the JVM will listen on the specified port for connections. When a connection is detected, the first byte of input will be read from the socket and then the connection will be immediately closed. An action will then be performed based on the byte read from the stream.

The easiest way to invoke an action manually is to telnet to the specified port and then type the single command key. telnet localhost 9999, for example.

Valid commands include:

• S : Shutdown cleanly.
• H : Immediate forced shutdown.
• R : Restart
• D : Perform a Thread Dump
• U : Unexpected shutdown. (Simulate a crash for testing)
• V : Cause an access violation. (For testing)
• G : Make the JVM appear to be hung. (For testing)

Additional user defined actions can be defined by calling the registerAction( byte command, Runnable action ) method. The Wrapper project reserves the right to define any upper case commands in the future. To avoid future conflicts, please use lower case for user defined commands.

This application will work even in most deadlock situations because the thread is in issolation from the rest of the application. If the JVM is truely hung, this class will fail to accept connections but the Wrapper itself will detect the hang and restart the JVM externally.

The following code can be used in your application to start up the WrapperActionServer with all default actions enabled:

  int port = 9999;
  WrapperActionServer server = new WrapperActionServer( port );
  server.enableShutdownAction( true );
  server.enableHaltExpectedAction( true );
  server.enableRestartAction( true );
  server.enableThreadDumpAction( true );
  server.enableHaltUnexpectedAction( true );
  server.enableAccessViolationAction( true );
  server.enableAppearHungAction( true );
  server.start();
 

Then remember to stop the server when your application shuts down:

  server.stop();
 

Author:

Tanuki Software Development Team <support@tanukisoftware.com>

Field Summary

Fields

Modifier and Type	Field and Description
static byte	COMMAND_ACCESS_VIOLATION Command to invoke an access violation.
static byte	COMMAND_APPEAR_HUNG Command to invoke an appear hung action.
static byte	COMMAND_DUMP Command to invoke a thread dump action.
static byte	COMMAND_HALT_EXPECTED Command to invoke an expected halt action.
static byte	COMMAND_HALT_UNEXPECTED Command to invoke an unexpected halt action.
static byte	COMMAND_RESTART Command to invoke a restart action.
static byte	COMMAND_SHUTDOWN Command to invoke a shutdown action.

Constructor Summary

Constructors

Constructor and Description
WrapperActionServer(int port) Creates and starts WrapperActionServer instance bound to the specified port.
WrapperActionServer(int port, java.net.InetAddress bindAddress) Creates and starts WrapperActionServer instance bound to the specified port and address.

Method Summary

Modifier and Type	Method and Description
void	enableAccessViolationAction(boolean enable) Enable or disable the access violation command.
void	enableAppearHungAction(boolean enable) Enable or disable the appear hung command.
void	enableHaltExpectedAction(boolean enable) Enable or disable the expected halt command.
void	enableHaltUnexpectedAction(boolean enable) Enable or disable the unexpected halt command.
void	enableRestartAction(boolean enable) Enable or disable the restart command.
void	enableShutdownAction(boolean enable) Enable or disable the shutdown command.
void	enableThreadDumpAction(boolean enable) Enable or disable the thread dump command.
void	registerAction(byte command, java.lang.Runnable action) Registers an action with the action server.
void	run() Thread which will listen for connections on the socket.
void	start() Starts the runner thread.
void	stop() Stops the runner thread, blocking until it has stopped.
void	unregisterAction(byte command) Unregisters an action with the given command.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

COMMAND_SHUTDOWN

public static final byte COMMAND_SHUTDOWN

Command to invoke a shutdown action.

See Also:

Constant Field Values

COMMAND_HALT_EXPECTED

public static final byte COMMAND_HALT_EXPECTED

Command to invoke an expected halt action.

See Also:

Constant Field Values

COMMAND_RESTART

public static final byte COMMAND_RESTART

Command to invoke a restart action.

See Also:

Constant Field Values

COMMAND_DUMP

public static final byte COMMAND_DUMP

Command to invoke a thread dump action.

See Also:

Constant Field Values

COMMAND_HALT_UNEXPECTED

public static final byte COMMAND_HALT_UNEXPECTED

Command to invoke an unexpected halt action.

See Also:

Constant Field Values

COMMAND_ACCESS_VIOLATION

public static final byte COMMAND_ACCESS_VIOLATION

Command to invoke an access violation.

See Also:

Constant Field Values

COMMAND_APPEAR_HUNG

public static final byte COMMAND_APPEAR_HUNG

Command to invoke an appear hung action.

See Also:

Constant Field Values

Constructor Detail

WrapperActionServer

public WrapperActionServer(int port,
                           java.net.InetAddress bindAddress)

Creates and starts WrapperActionServer instance bound to the specified port and address.

Parameters:

port - Port on which to listen for connections.

bindAddress - Address to bind to.

WrapperActionServer

public WrapperActionServer(int port)

Creates and starts WrapperActionServer instance bound to the specified port. The socket will bind to all addresses and should be concidered a security risk.

Parameters:

port - Port on which to listen for connections.

Method Detail

run

public void run()

Thread which will listen for connections on the socket.

Specified by:

run in interface java.lang.Runnable

start

public void start()
           throws java.io.IOException

Starts the runner thread.

Throws:

java.io.IOException - If the server socket is unable to bind to the specified port or there are any other problems opening a socket.

stop

public void stop()
          throws java.lang.Exception

Stops the runner thread, blocking until it has stopped.

Throws:

java.lang.Exception - If the thread is unable to interrupt.

registerAction

public void registerAction(byte command,
                           java.lang.Runnable action)

Registers an action with the action server. The server will not accept any new connections until an action has returned, so keep that in mind when writing them. Also be aware than any uncaught exceptions will be dumped to the console if uncaught by the action. To avoid this, wrap the code in a try { ... } catch (Throwable t) { ... } block.

Parameters:

command - Command to be registered. Will override any exiting action already registered with the same command.

action - Action to be registered.

unregisterAction

public void unregisterAction(byte command)

Unregisters an action with the given command. If no action exists with the specified command, the method will quietly ignore the call.

Parameters:

command - Command to be unregistered.

enableShutdownAction

public void enableShutdownAction(boolean enable)

Enable or disable the shutdown command. Disabled by default.

Parameters:

enable - True to enable to action, false to disable it.

enableHaltExpectedAction

public void enableHaltExpectedAction(boolean enable)

Enable or disable the expected halt command. Disabled by default. This will shutdown the JVM, but will do so immediately without going through the clean shutdown process.

Parameters:

enable - True to enable to action, false to disable it.

enableRestartAction

public void enableRestartAction(boolean enable)

Enable or disable the restart command. Disabled by default.

Parameters:

enable - True to enable to action, false to disable it.

enableThreadDumpAction

public void enableThreadDumpAction(boolean enable)

Enable or disable the thread dump command. Disabled by default.

Parameters:

enable - True to enable to action, false to disable it.

enableHaltUnexpectedAction

public void enableHaltUnexpectedAction(boolean enable)

Enable or disable the unexpected halt command. Disabled by default. If this command is executed, the Wrapper will think the JVM crashed and restart it.

Parameters:

enable - True to enable to action, false to disable it.

enableAccessViolationAction

public void enableAccessViolationAction(boolean enable)

Enable or disable the access violation command. Disabled by default. This command is useful for testing how an application handles the worst case situation where the JVM suddenly crashed. When this happens, the the JVM will simply die and there will be absolutely no chance for any shutdown or cleanup work to be done by the JVM.

Parameters:

enable - True to enable to action, false to disable it.

enableAppearHungAction

public void enableAppearHungAction(boolean enable)

Enable or disable the appear hung command. Disabled by default. This command is useful for testing how an application handles the situation where the JVM stops responding to the Wrapper's ping requests. This can happen if the JVM hangs or some piece of code deadlocks. When this happens, the Wrapper will give up after the ping timeout has expired and kill the JVM process. The JVM will not have a chance to clean up and shudown gracefully.

Parameters:

enable - True to enable to action, false to disable it.