The AWTAutoShutdown.java Java example source code
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package sun.awt;
import java.awt.AWTEvent;
import java.util.Collections;
import java.util.HashSet;
import java.util.IdentityHashMap;
import java.util.Map;
import java.util.Set;
import sun.util.logging.PlatformLogger;
/**
* This class is to let AWT shutdown automatically when a user is done
* with AWT. It tracks AWT state using the following parameters:
* <ul>
* <li>peerMap - the map between the existing peer objects
* and their associated targets
* <li>toolkitThreadBusy - whether the toolkit thread
* is waiting for a new native event to appear in its queue
* or is dispatching an event
* <li>busyThreadSet - a set of all the event dispatch
* threads that are busy at this moment, i.e. those that are not
* waiting for a new event to appear in their event queue.
* </ul>
* AWT is considered to be in ready-to-shutdown state when
* <code>peerMap is empty and toolkitThreadBusy
* is false and <code>busyThreadSet is empty.
* The internal AWTAutoShutdown logic secures that the single non-daemon
* thread (<code>blockerThread) is running when AWT is not in
* ready-to-shutdown state. This blocker thread is to prevent AWT from
* exiting since the toolkit thread is now daemon and all the event
* dispatch threads are started only when needed. Once it is detected
* that AWT is in ready-to-shutdown state this blocker thread waits
* for a certain timeout and if AWT state doesn't change during timeout
* this blocker thread terminates all the event dispatch threads and
* exits.
*/
public final class AWTAutoShutdown implements Runnable {
private static final AWTAutoShutdown theInstance = new AWTAutoShutdown();
/**
* This lock object is used to synchronize shutdown operations.
*/
private final Object mainLock = new Object();
/**
* This lock object is to secure that when a new blocker thread is
* started it will be the first who acquire the main lock after
* the thread that created the new blocker released the main lock
* by calling lock.wait() to wait for the blocker to start.
*/
private final Object activationLock = new Object();
/**
* This set keeps references to all the event dispatch threads that
* are busy at this moment, i.e. those that are not waiting for a
* new event to appear in their event queue.
* Access is synchronized on the main lock object.
*/
private final Set<Thread> busyThreadSet = new HashSet<>(7);
/**
* Indicates whether the toolkit thread is waiting for a new native
* event to appear or is dispatching an event.
*/
private boolean toolkitThreadBusy = false;
/**
* This is a map between components and their peers.
* we should work with in under activationLock&mainLock lock.
*/
private final Map<Object, Object> peerMap = new IdentityHashMap<>();
/**
* References the alive non-daemon thread that is currently used
* for keeping AWT from exiting.
*/
private Thread blockerThread = null;
/**
* We need this flag to secure that AWT state hasn't changed while
* we were waiting for the safety timeout to pass.
*/
private boolean timeoutPassed = false;
/**
* Once we detect that AWT is ready to shutdown we wait for a certain
* timeout to pass before stopping event dispatch threads.
*/
private static final int SAFETY_TIMEOUT = 1000;
/**
* Constructor method is intentionally made private to secure
* a single instance. Use getInstance() to reference it.
*
* @see AWTAutoShutdown#getInstance
*/
private AWTAutoShutdown() {}
/**
* Returns reference to a single AWTAutoShutdown instance.
*/
public static AWTAutoShutdown getInstance() {
return theInstance;
}
/**
* Notify that the toolkit thread is not waiting for a native event
* to appear in its queue.
*
* @see AWTAutoShutdown#notifyToolkitThreadFree
* @see AWTAutoShutdown#setToolkitBusy
* @see AWTAutoShutdown#isReadyToShutdown
*/
public static void notifyToolkitThreadBusy() {
getInstance().setToolkitBusy(true);
}
/**
* Notify that the toolkit thread is waiting for a native event
* to appear in its queue.
*
* @see AWTAutoShutdown#notifyToolkitThreadFree
* @see AWTAutoShutdown#setToolkitBusy
* @see AWTAutoShutdown#isReadyToShutdown
*/
public static void notifyToolkitThreadFree() {
getInstance().setToolkitBusy(false);
}
/**
* Add a specified thread to the set of busy event dispatch threads.
* If this set already contains the specified thread or the thread is null,
* the call leaves this set unchanged and returns silently.
*
* @param thread thread to be added to this set, if not present.
* @see AWTAutoShutdown#notifyThreadFree
* @see AWTAutoShutdown#isReadyToShutdown
*/
public void notifyThreadBusy(final Thread thread) {
if (thread == null) {
return;
}
synchronized (activationLock) {
synchronized (mainLock) {
if (blockerThread == null) {
activateBlockerThread();
} else if (isReadyToShutdown()) {
mainLock.notifyAll();
timeoutPassed = false;
}
busyThreadSet.add(thread);
}
}
}
/**
* Remove a specified thread from the set of busy event dispatch threads.
* If this set doesn't contain the specified thread or the thread is null,
* the call leaves this set unchanged and returns silently.
*
* @param thread thread to be removed from this set, if present.
* @see AWTAutoShutdown#notifyThreadBusy
* @see AWTAutoShutdown#isReadyToShutdown
*/
public void notifyThreadFree(final Thread thread) {
if (thread == null) {
return;
}
synchronized (activationLock) {
synchronized (mainLock) {
busyThreadSet.remove(thread);
if (isReadyToShutdown()) {
mainLock.notifyAll();
timeoutPassed = false;
}
}
}
}
/**
* Notify that the peermap has been updated, that means a new peer
* has been created or some existing peer has been disposed.
*
* @see AWTAutoShutdown#isReadyToShutdown
*/
void notifyPeerMapUpdated() {
synchronized (activationLock) {
synchronized (mainLock) {
if (!isReadyToShutdown() && blockerThread == null) {
activateBlockerThread();
} else {
mainLock.notifyAll();
timeoutPassed = false;
}
}
}
}
/**
* Determine whether AWT is currently in ready-to-shutdown state.
* AWT is considered to be in ready-to-shutdown state if
* <code>peerMap is empty and toolkitThreadBusy
* is false and <code>busyThreadSet is empty.
*
* @return true if AWT is in ready-to-shutdown state.
*/
private boolean isReadyToShutdown() {
return (!toolkitThreadBusy &&
peerMap.isEmpty() &&
busyThreadSet.isEmpty());
}
/**
* Notify about the toolkit thread state change.
*
* @param busy true if the toolkit thread state changes from idle
* to busy.
* @see AWTAutoShutdown#notifyToolkitThreadBusy
* @see AWTAutoShutdown#notifyToolkitThreadFree
* @see AWTAutoShutdown#isReadyToShutdown
*/
private void setToolkitBusy(final boolean busy) {
if (busy != toolkitThreadBusy) {
synchronized (activationLock) {
synchronized (mainLock) {
if (busy != toolkitThreadBusy) {
if (busy) {
if (blockerThread == null) {
activateBlockerThread();
} else if (isReadyToShutdown()) {
mainLock.notifyAll();
timeoutPassed = false;
}
toolkitThreadBusy = busy;
} else {
toolkitThreadBusy = busy;
if (isReadyToShutdown()) {
mainLock.notifyAll();
timeoutPassed = false;
}
}
}
}
}
}
}
/**
* Implementation of the Runnable interface.
* Incapsulates the blocker thread functionality.
*
* @see AWTAutoShutdown#isReadyToShutdown
*/
public void run() {
Thread currentThread = Thread.currentThread();
boolean interrupted = false;
synchronized (mainLock) {
try {
/* Notify that the thread is started. */
mainLock.notifyAll();
while (blockerThread == currentThread) {
mainLock.wait();
timeoutPassed = false;
/*
* This loop is introduced to handle the following case:
* it is possible that while we are waiting for the
* safety timeout to pass AWT state can change to
* not-ready-to-shutdown and back to ready-to-shutdown.
* In this case we have to wait once again.
* NOTE: we shouldn't break into the outer loop
* in this case, since we may never be notified
* in an outer infinite wait at this point.
*/
while (isReadyToShutdown()) {
if (timeoutPassed) {
timeoutPassed = false;
blockerThread = null;
break;
}
timeoutPassed = true;
mainLock.wait(SAFETY_TIMEOUT);
}
}
} catch (InterruptedException e) {
interrupted = true;
} finally {
if (blockerThread == currentThread) {
blockerThread = null;
}
}
}
if (!interrupted) {
AppContext.stopEventDispatchThreads();
}
}
@SuppressWarnings("serial")
static AWTEvent getShutdownEvent() {
return new AWTEvent(getInstance(), 0) {
};
}
/**
* Creates and starts a new blocker thread. Doesn't return until
* the new blocker thread starts.
*/
private void activateBlockerThread() {
Thread thread = new Thread(this, "AWT-Shutdown");
thread.setDaemon(false);
blockerThread = thread;
thread.start();
try {
/* Wait for the blocker thread to start. */
mainLock.wait();
} catch (InterruptedException e) {
System.err.println("AWT blocker activation interrupted:");
e.printStackTrace();
}
}
final void registerPeer(final Object target, final Object peer) {
synchronized (activationLock) {
synchronized (mainLock) {
peerMap.put(target, peer);
notifyPeerMapUpdated();
}
}
}
final void unregisterPeer(final Object target, final Object peer) {
synchronized (activationLock) {
synchronized (mainLock) {
if (peerMap.get(target) == peer) {
peerMap.remove(target);
notifyPeerMapUpdated();
}
}
}
}
final Object getPeer(final Object target) {
synchronized (activationLock) {
synchronized (mainLock) {
return peerMap.get(target);
}
}
}
final void dumpPeers(final PlatformLogger aLog) {
if (aLog.isLoggable(PlatformLogger.Level.FINE)) {
synchronized (activationLock) {
synchronized (mainLock) {
aLog.fine("Mapped peers:");
for (Object key : peerMap.keySet()) {
aLog.fine(key + "->" + peerMap.get(key));
}
}
}
}
}
} // class AWTAutoShutdown
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