/* * Copyright (c) 1998, 2008, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package sun.misc; import java.security.AccessController; import java.security.PrivilegedAction; import java.util.SortedSet; import java.util.TreeSet; /** * Support for garbage-collection latency requests. * * @author Mark Reinhold * @since 1.2 */ public class GC { private GC() { } /* To prevent instantiation */ /* Latency-target value indicating that there's no active target */ private static final long NO_TARGET = Long.MAX_VALUE; /* The current latency target, or NO_TARGET if there is no target */ private static long latencyTarget = NO_TARGET; /* The daemon thread that implements the latency-target mechanism, * or null if there is presently no daemon thread */ private static Thread daemon = null; /* The lock object for the latencyTarget and daemon fields. The daemon * thread, if it exists, waits on this lock for notification that the * latency target has changed. */ private static class LatencyLock extends Object { }; private static Object lock = new LatencyLock(); /** * Returns the maximum object-inspection age, which is the number * of real-time milliseconds that have elapsed since the * least-recently-inspected heap object was last inspected by the garbage * collector. * *
For simple stop-the-world collectors this value is just the time * since the most recent collection. For generational collectors it is the * time since the oldest generation was most recently collected. Other * collectors are free to return a pessimistic estimate of the elapsed * time, or simply the time since the last full collection was performed. * *
Note that in the presence of reference objects, a given object that
* is no longer strongly reachable may have to be inspected multiple times
* before it can be reclaimed.
*/
public static native long maxObjectInspectionAge();
private static class Daemon extends Thread {
public void run() {
for (;;) {
long l;
synchronized (lock) {
l = latencyTarget;
if (l == NO_TARGET) {
/* No latency target, so exit */
GC.daemon = null;
return;
}
long d = maxObjectInspectionAge();
if (d >= l) {
/* Do a full collection. There is a remote possibility
* that a full collection will occurr between the time
* we sample the inspection age and the time the GC
* actually starts, but this is sufficiently unlikely
* that it doesn't seem worth the more expensive JVM
* interface that would be required.
*/
System.gc();
d = 0;
}
/* Wait for the latency period to expire,
* or for notification that the period has changed
*/
try {
lock.wait(l - d);
} catch (InterruptedException x) {
continue;
}
}
}
}
private Daemon(ThreadGroup tg) {
super(tg, "GC Daemon");
}
/* Create a new daemon thread in the root thread group */
public static void create() {
PrivilegedAction{@link #requestLatency}
* method. Given a request, the only interesting operation is that of
* cancellation.
*/
public static class LatencyRequest
implements Comparablelatency
is non-positive
*/
public static LatencyRequest requestLatency(long latency) {
return new LatencyRequest(latency);
}
/**
* Returns the current smallest garbage-collection latency request, or zero
* if there are no active requests.
*/
public static long currentLatencyTarget() {
long t = latencyTarget;
return (t == NO_TARGET) ? 0 : t;
}
}