Class 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();
     
    • Constructor Summary

      Constructors 
      Constructor 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

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method 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.