| /* |
| * 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.rmi.transport; |
| |
| import java.security.AccessController; |
| import java.security.PrivilegedAction; |
| import java.util.SortedSet; |
| import java.util.TreeSet; |
| import jdk.internal.misc.InnocuousThread; |
| |
| |
| /** |
| * Support for garbage-collection latency requests. |
| * |
| * @author Mark Reinhold |
| * @since 1.2 |
| */ |
| |
| 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(); |
| |
| static { |
| AccessController.doPrivileged(new PrivilegedAction<Void>() { |
| public Void run() { |
| System.loadLibrary("rmi"); |
| return null; |
| }}); |
| } |
| |
| private static class Daemon implements Runnable { |
| |
| @Override |
| 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; |
| } |
| } |
| } |
| } |
| |
| /* Create a new daemon thread */ |
| public static void create() { |
| PrivilegedAction<Void> pa = new PrivilegedAction<Void>() { |
| public Void run() { |
| Thread t = InnocuousThread.newSystemThread("RMI GC Daemon", |
| new Daemon()); |
| assert t.getContextClassLoader() == null; |
| t.setDaemon(true); |
| t.setPriority(Thread.MIN_PRIORITY + 1); |
| t.start(); |
| GC.daemon = t; |
| 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; |
| } |
| |
| } |