--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/java.base/share/classes/sun/misc/GC.java Sun Aug 17 15:54:13 2014 +0100
@@ -0,0 +1,284 @@
+/*
+ * 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 <em>object-inspection age</em>, 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.
+ *
+ * <p> 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.
+ *
+ * <p> 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<Void> pa = new PrivilegedAction<Void>() {
+ public Void run() {
+ ThreadGroup tg = Thread.currentThread().getThreadGroup();
+ for (ThreadGroup tgn = tg;
+ tgn != null;
+ tg = tgn, tgn = tg.getParent());
+ Daemon d = new Daemon(tg);
+ d.setDaemon(true);
+ d.setPriority(Thread.MIN_PRIORITY + 1);
+ d.start();
+ GC.daemon = d;
+ return null;
+ }};
+ AccessController.doPrivileged(pa);
+ }
+
+ }
+
+
+ /* Sets the latency target to the given value.
+ * Must be invoked while holding the lock.
+ */
+ private static void setLatencyTarget(long ms) {
+ latencyTarget = ms;
+ if (daemon == null) {
+ /* Create a new daemon thread */
+ Daemon.create();
+ } else {
+ /* Notify the existing daemon thread
+ * that the lateency target has changed
+ */
+ lock.notify();
+ }
+ }
+
+
+ /**
+ * Represents an active garbage-collection latency request. Instances of
+ * this class are created by the <code>{@link #requestLatency}</code>
+ * method. Given a request, the only interesting operation is that of
+ * cancellation.
+ */
+ public static class LatencyRequest
+ implements Comparable<LatencyRequest> {
+
+ /* Instance counter, used to generate unique identifers */
+ private static long counter = 0;
+
+ /* Sorted set of active latency requests */
+ private static SortedSet<LatencyRequest> requests = null;
+
+ /* Examine the request set and reset the latency target if necessary.
+ * Must be invoked while holding the lock.
+ */
+ private static void adjustLatencyIfNeeded() {
+ if ((requests == null) || requests.isEmpty()) {
+ if (latencyTarget != NO_TARGET) {
+ setLatencyTarget(NO_TARGET);
+ }
+ } else {
+ LatencyRequest r = requests.first();
+ if (r.latency != latencyTarget) {
+ setLatencyTarget(r.latency);
+ }
+ }
+ }
+
+ /* The requested latency, or NO_TARGET
+ * if this request has been cancelled
+ */
+ private long latency;
+
+ /* Unique identifier for this request */
+ private long id;
+
+ private LatencyRequest(long ms) {
+ if (ms <= 0) {
+ throw new IllegalArgumentException("Non-positive latency: "
+ + ms);
+ }
+ this.latency = ms;
+ synchronized (lock) {
+ this.id = ++counter;
+ if (requests == null) {
+ requests = new TreeSet<LatencyRequest>();
+ }
+ requests.add(this);
+ adjustLatencyIfNeeded();
+ }
+ }
+
+ /**
+ * Cancels this latency request.
+ *
+ * @throws IllegalStateException
+ * If this request has already been cancelled
+ */
+ public void cancel() {
+ synchronized (lock) {
+ if (this.latency == NO_TARGET) {
+ throw new IllegalStateException("Request already"
+ + " cancelled");
+ }
+ if (!requests.remove(this)) {
+ throw new InternalError("Latency request "
+ + this + " not found");
+ }
+ if (requests.isEmpty()) requests = null;
+ this.latency = NO_TARGET;
+ adjustLatencyIfNeeded();
+ }
+ }
+
+ public int compareTo(LatencyRequest r) {
+ long d = this.latency - r.latency;
+ if (d == 0) d = this.id - r.id;
+ return (d < 0) ? -1 : ((d > 0) ? +1 : 0);
+ }
+
+ public String toString() {
+ return (LatencyRequest.class.getName()
+ + "[" + latency + "," + id + "]");
+ }
+
+ }
+
+
+ /**
+ * Makes a new request for a garbage-collection latency of the given
+ * number of real-time milliseconds. A low-priority daemon thread makes a
+ * best effort to ensure that the maximum object-inspection age never
+ * exceeds the smallest of the currently active requests.
+ *
+ * @param latency
+ * The requested latency
+ *
+ * @throws IllegalArgumentException
+ * If the given <code>latency</code> 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;
+ }
+
+}