The Android Open Source Project | b5de22c | 2012-04-01 00:00:00 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2011 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | package java.lang; |
| 18 | |
| 19 | import dalvik.system.VMRuntime; |
| 20 | import java.lang.ref.FinalizerReference; |
| 21 | import java.lang.ref.Reference; |
| 22 | import java.lang.ref.ReferenceQueue; |
| 23 | import java.util.concurrent.TimeoutException; |
| 24 | import libcore.util.EmptyArray; |
| 25 | |
| 26 | /** |
| 27 | * Calls Object.finalize() on objects in the finalizer reference queue. The VM |
| 28 | * will abort if any finalize() call takes more than the maximum finalize time |
| 29 | * to complete. |
| 30 | * |
| 31 | * @hide |
| 32 | */ |
| 33 | public final class Daemons { |
| 34 | private static final int NANOS_PER_MILLI = 1000 * 1000; |
| 35 | private static final int NANOS_PER_SECOND = NANOS_PER_MILLI * 1000; |
| 36 | private static final long MAX_FINALIZE_NANOS = 10L * NANOS_PER_SECOND; |
| 37 | |
| 38 | public static void start() { |
| 39 | ReferenceQueueDaemon.INSTANCE.start(); |
| 40 | FinalizerDaemon.INSTANCE.start(); |
| 41 | FinalizerWatchdogDaemon.INSTANCE.start(); |
| 42 | } |
| 43 | |
| 44 | public static void stop() { |
| 45 | ReferenceQueueDaemon.INSTANCE.stop(); |
| 46 | FinalizerDaemon.INSTANCE.stop(); |
| 47 | FinalizerWatchdogDaemon.INSTANCE.stop(); |
| 48 | } |
| 49 | |
| 50 | /** |
| 51 | * A background task that provides runtime support to the application. |
| 52 | * Daemons can be stopped and started, but only so that the zygote can be a |
| 53 | * single-threaded process when it forks. |
| 54 | */ |
| 55 | private static abstract class Daemon implements Runnable { |
| 56 | private Thread thread; |
| 57 | |
| 58 | public synchronized void start() { |
| 59 | if (thread != null) { |
| 60 | throw new IllegalStateException("already running"); |
| 61 | } |
| 62 | thread = new Thread(ThreadGroup.mSystem, this, |
| 63 | getClass().getSimpleName()); |
| 64 | thread.setDaemon(true); |
| 65 | thread.start(); |
| 66 | } |
| 67 | |
| 68 | public abstract void run(); |
| 69 | |
| 70 | /** |
| 71 | * Returns true while the current thread should continue to run; false |
| 72 | * when it should return. |
| 73 | */ |
| 74 | protected synchronized boolean isRunning() { |
| 75 | return thread != null; |
| 76 | } |
| 77 | |
| 78 | public synchronized void interrupt() { |
| 79 | if (thread == null) { |
| 80 | throw new IllegalStateException("not running"); |
| 81 | } |
| 82 | thread.interrupt(); |
| 83 | } |
| 84 | |
| 85 | /** |
| 86 | * Waits for the runtime thread to stop. This interrupts the thread |
| 87 | * currently running the runnable and then waits for it to exit. |
| 88 | */ |
| 89 | public void stop() { |
| 90 | Thread threadToStop; |
| 91 | synchronized (this) { |
| 92 | threadToStop = thread; |
| 93 | thread = null; |
| 94 | } |
| 95 | if (threadToStop == null) { |
| 96 | throw new IllegalStateException("not running"); |
| 97 | } |
| 98 | threadToStop.interrupt(); |
| 99 | while (true) { |
| 100 | try { |
| 101 | threadToStop.join(); |
| 102 | return; |
| 103 | } catch (InterruptedException ignored) { |
| 104 | } |
| 105 | } |
| 106 | } |
| 107 | |
| 108 | /** |
| 109 | * Returns the current stack trace of the thread, or an empty stack trace |
| 110 | * if the thread is not currently running. |
| 111 | */ |
| 112 | public synchronized StackTraceElement[] getStackTrace() { |
| 113 | return thread != null ? thread.getStackTrace() : EmptyArray.STACK_TRACE_ELEMENT; |
| 114 | } |
| 115 | } |
| 116 | |
| 117 | /** |
| 118 | * This heap management thread moves elements from the garbage collector's |
| 119 | * pending list to the managed reference queue. |
| 120 | */ |
| 121 | private static class ReferenceQueueDaemon extends Daemon { |
| 122 | private static final ReferenceQueueDaemon INSTANCE = new ReferenceQueueDaemon(); |
| 123 | |
| 124 | @Override public void run() { |
| 125 | while (isRunning()) { |
| 126 | Reference<?> list; |
| 127 | try { |
| 128 | synchronized (ReferenceQueue.class) { |
| 129 | while (ReferenceQueue.unenqueued == null) { |
| 130 | ReferenceQueue.class.wait(); |
| 131 | } |
| 132 | list = ReferenceQueue.unenqueued; |
| 133 | ReferenceQueue.unenqueued = null; |
| 134 | } |
| 135 | } catch (InterruptedException e) { |
| 136 | continue; |
| 137 | } |
| 138 | enqueue(list); |
| 139 | } |
| 140 | } |
| 141 | |
| 142 | private void enqueue(Reference<?> list) { |
| 143 | while (list != null) { |
| 144 | Reference<?> reference; |
| 145 | // pendingNext is owned by the GC so no synchronization is required |
| 146 | if (list == list.pendingNext) { |
| 147 | reference = list; |
| 148 | reference.pendingNext = null; |
| 149 | list = null; |
| 150 | } else { |
| 151 | reference = list.pendingNext; |
| 152 | list.pendingNext = reference.pendingNext; |
| 153 | reference.pendingNext = null; |
| 154 | } |
| 155 | reference.enqueueInternal(); |
| 156 | } |
| 157 | } |
| 158 | } |
| 159 | |
| 160 | private static class FinalizerDaemon extends Daemon { |
| 161 | private static final FinalizerDaemon INSTANCE = new FinalizerDaemon(); |
| 162 | private final ReferenceQueue<Object> queue = FinalizerReference.queue; |
| 163 | private volatile Object finalizingObject; |
| 164 | private volatile long finalizingStartedNanos; |
| 165 | |
| 166 | @Override public void run() { |
| 167 | while (isRunning()) { |
| 168 | // Take a reference, blocking until one is ready or the thread should stop |
| 169 | try { |
| 170 | doFinalize((FinalizerReference<?>) queue.remove()); |
| 171 | } catch (InterruptedException ignored) { |
| 172 | } |
| 173 | } |
| 174 | } |
| 175 | |
| 176 | @FindBugsSuppressWarnings("FI_EXPLICIT_INVOCATION") |
| 177 | private void doFinalize(FinalizerReference<?> reference) { |
| 178 | FinalizerReference.remove(reference); |
| 179 | Object object = reference.get(); |
| 180 | reference.clear(); |
| 181 | try { |
| 182 | finalizingStartedNanos = System.nanoTime(); |
| 183 | finalizingObject = object; |
| 184 | synchronized (FinalizerWatchdogDaemon.INSTANCE) { |
| 185 | FinalizerWatchdogDaemon.INSTANCE.notify(); |
| 186 | } |
| 187 | object.finalize(); |
| 188 | } catch (Throwable ex) { |
| 189 | // The RI silently swallows these, but Android has always logged. |
| 190 | System.logE("Uncaught exception thrown by finalizer", ex); |
| 191 | } finally { |
| 192 | finalizingObject = null; |
| 193 | } |
| 194 | } |
| 195 | } |
| 196 | |
| 197 | /** |
| 198 | * The watchdog exits the VM if the finalizer ever gets stuck. We consider |
| 199 | * the finalizer to be stuck if it spends more than MAX_FINALIZATION_MILLIS |
| 200 | * on one instance. |
| 201 | */ |
| 202 | private static class FinalizerWatchdogDaemon extends Daemon { |
| 203 | private static final FinalizerWatchdogDaemon INSTANCE = new FinalizerWatchdogDaemon(); |
| 204 | |
| 205 | @Override public void run() { |
| 206 | while (isRunning()) { |
| 207 | Object object = waitForObject(); |
| 208 | if (object == null) { |
| 209 | // We have been interrupted, need to see if this daemon has been stopped. |
| 210 | continue; |
| 211 | } |
| 212 | boolean finalized = waitForFinalization(object); |
| 213 | if (!finalized && !VMRuntime.getRuntime().isDebuggerActive()) { |
| 214 | finalizerTimedOut(object); |
| 215 | break; |
| 216 | } |
| 217 | } |
| 218 | } |
| 219 | |
| 220 | private Object waitForObject() { |
| 221 | while (true) { |
| 222 | Object object = FinalizerDaemon.INSTANCE.finalizingObject; |
| 223 | if (object != null) { |
| 224 | return object; |
| 225 | } |
| 226 | synchronized (this) { |
| 227 | // wait until something is ready to be finalized |
| 228 | // http://code.google.com/p/android/issues/detail?id=22778 |
| 229 | try { |
| 230 | wait(); |
| 231 | } catch (InterruptedException e) { |
| 232 | // Daemon.stop may have interrupted us. |
| 233 | return null; |
| 234 | } |
| 235 | } |
| 236 | } |
| 237 | } |
| 238 | |
| 239 | private void sleepFor(long startNanos, long durationNanos) { |
| 240 | while (true) { |
| 241 | long elapsedNanos = System.nanoTime() - startNanos; |
| 242 | long sleepNanos = durationNanos - elapsedNanos; |
| 243 | long sleepMills = sleepNanos / NANOS_PER_MILLI; |
| 244 | if (sleepMills <= 0) { |
| 245 | return; |
| 246 | } |
| 247 | try { |
| 248 | Thread.sleep(sleepMills); |
| 249 | } catch (InterruptedException e) { |
| 250 | if (!isRunning()) { |
| 251 | return; |
| 252 | } |
| 253 | } |
| 254 | } |
| 255 | } |
| 256 | |
| 257 | private boolean waitForFinalization(Object object) { |
| 258 | sleepFor(FinalizerDaemon.INSTANCE.finalizingStartedNanos, MAX_FINALIZE_NANOS); |
| 259 | return object != FinalizerDaemon.INSTANCE.finalizingObject; |
| 260 | } |
| 261 | |
| 262 | private static void finalizerTimedOut(Object object) { |
| 263 | // The current object has exceeded the finalization deadline; abort! |
| 264 | String message = object.getClass().getName() + ".finalize() timed out after " |
| 265 | + (MAX_FINALIZE_NANOS / NANOS_PER_SECOND) + " seconds"; |
| 266 | Exception syntheticException = new TimeoutException(message); |
| 267 | // We use the stack from where finalize() was running to show where it was stuck. |
| 268 | syntheticException.setStackTrace(FinalizerDaemon.INSTANCE.getStackTrace()); |
| 269 | Thread.UncaughtExceptionHandler h = Thread.getDefaultUncaughtExceptionHandler(); |
| 270 | if (h == null) { |
| 271 | // If we have no handler, log and exit. |
| 272 | System.logE(message, syntheticException); |
| 273 | System.exit(2); |
| 274 | } |
| 275 | // Otherwise call the handler to do crash reporting. |
| 276 | // We don't just throw because we're not the thread that |
| 277 | // timed out; we're the thread that detected it. |
| 278 | h.uncaughtException(Thread.currentThread(), syntheticException); |
| 279 | } |
| 280 | } |
| 281 | } |