alma.ACS.MasterComponentImpl

Class StateChangeSemaphore

java.lang.Object

alma.ACS.MasterComponentImpl.StateChangeSemaphore

public class StateChangeSemaphore
extends java.lang.Object

Helper class that allows to synchronize the sending of events with the state changes due to previous events. Note that state changes occur asynchronously when triggered by activity states.

This class is abstracted from concrete state change notification APIs so that subclasses can be implemented as such listeners; they must call stateChangedNotify() upon notification by the state machine.

Author:

hsommer created Apr 30, 2004 9:50:34 AM

Constructor Summary

Constructors

Constructor and Description
StateChangeSemaphore(java.util.logging.Logger logger)

Method Summary

Modifier and Type	Method and Description
void	reset() Resets the state change notification count.
protected void	stateChangedNotify() To be called from state change listener method of subclass.
void	waitForStateChanges(int count) Blocks until the specified number of state change notifications have been received since last call to reset().

Methods inherited from class java.lang.Object

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

Constructor Detail

StateChangeSemaphore

public StateChangeSemaphore(java.util.logging.Logger logger)

Method Detail

stateChangedNotify

protected void stateChangedNotify()

To be called from state change listener method of subclass.

This call is expected to come from a different thread than the one that calls waitForStateChanges. Both methods are synchronized, but there will not be a deadlock, since waitForStateChanges yields ownership of the monitor when calling wait.

waitForStateChanges

public void waitForStateChanges(int count)
                         throws java.lang.InterruptedException

Blocks until the specified number of state change notifications have been received since last call to reset().

Does not block at all if at least count state change notifications have been received since the last call to reset. Otherwise only blocks until the missing number of notifications has arrived. Before returning, this method subtracts count from the internal counter for state change notifications, which allows a client to catch up with fast firing event notifications by calling this method several times.

Note that the "synchronized" modifier is required in order for the client thread to obtain ownership of this semaphore (i.e. its monitor), without which the thread synchronization would not work. See Object.notify() for an explanation.

Parameters:

count - number of state change notifications that must be received since last call to reset() so that this call will return

Throws:

java.lang.InterruptedException

reset

public void reset()

Resets the state change notification count. Must be called prior to sending a state event.