/*
* Copyright (C) 2011 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package java.lang;
import android.system.Os;
import android.system.OsConstants;
import dalvik.system.VMRuntime;
import java.lang.ref.FinalizerReference;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.TimeoutException;
import libcore.util.EmptyArray;
/**
* Calls Object.finalize() on objects in the finalizer reference queue. The VM
* will abort if any finalize() call takes more than the maximum finalize time
* to complete.
*
* @hide
*/
public final class Daemons {
private static final int NANOS_PER_MILLI = 1000 * 1000;
private static final int NANOS_PER_SECOND = NANOS_PER_MILLI * 1000;
private static final long MAX_FINALIZE_NANOS = 10L * NANOS_PER_SECOND;
public static void start() {
ReferenceQueueDaemon.INSTANCE.start();
FinalizerDaemon.INSTANCE.start();
FinalizerWatchdogDaemon.INSTANCE.start();
HeapTaskDaemon.INSTANCE.start();
}
public static void startPostZygoteFork() {
ReferenceQueueDaemon.INSTANCE.startPostZygoteFork();
FinalizerDaemon.INSTANCE.startPostZygoteFork();
FinalizerWatchdogDaemon.INSTANCE.startPostZygoteFork();
HeapTaskDaemon.INSTANCE.startPostZygoteFork();
}
public static void stop() {
HeapTaskDaemon.INSTANCE.stop();
ReferenceQueueDaemon.INSTANCE.stop();
FinalizerDaemon.INSTANCE.stop();
FinalizerWatchdogDaemon.INSTANCE.stop();
}
/**
* A background task that provides runtime support to the application.
* Daemons can be stopped and started, but only so that the zygote can be a
* single-threaded process when it forks.
*/
private static abstract class Daemon implements Runnable {
private Thread thread;
private String name;
private boolean postZygoteFork;
protected Daemon(String name) {
this.name = name;
}
public synchronized void start() {
startInternal();
}
public synchronized void startPostZygoteFork() {
postZygoteFork = true;
startInternal();
}
public void startInternal() {
if (thread != null) {
throw new IllegalStateException("already running");
}
thread = new Thread(ThreadGroup.systemThreadGroup, this, name);
thread.setDaemon(true);
thread.start();
}
public void run() {
if (postZygoteFork) {
// We don't set the priority before the Thread.start() call above because
// Thread.start() will call SetNativePriority and overwrite the desired native
// priority. We (may) use a native priority that doesn't have a corresponding
// java.lang.Thread-level priority (native priorities are more coarse-grained.)
VMRuntime.getRuntime().setSystemDaemonThreadPriority();
}
runInternal();
}
public abstract void runInternal();
/**
* Returns true while the current thread should continue to run; false
* when it should return.
*/
protected synchronized boolean isRunning() {
return thread != null;
}
public synchronized void interrupt() {
interrupt(thread);
}
public synchronized void interrupt(Thread thread) {
if (thread == null) {
throw new IllegalStateException("not running");
}
thread.interrupt();
}
/**
* Waits for the runtime thread to stop. This interrupts the thread
* currently running the runnable and then waits for it to exit.
*/
public void stop() {
Thread threadToStop;
synchronized (this) {
threadToStop = thread;
thread = null;
}
if (threadToStop == null) {
throw new IllegalStateException("not running");
}
interrupt(threadToStop);
while (true) {
try {
threadToStop.join();
return;
} catch (InterruptedException ignored) {
} catch (OutOfMemoryError ignored) {
// An OOME may be thrown if allocating the InterruptedException failed.
}
}
}
/**
* Returns the current stack trace of the thread, or an empty stack trace
* if the thread is not currently running.
*/
public synchronized StackTraceElement[] getStackTrace() {
return thread != null ? thread.getStackTrace() : EmptyArray.STACK_TRACE_ELEMENT;
}
}
/**
* This heap management thread moves elements from the garbage collector's
* pending list to the managed reference queue.
*/
private static class ReferenceQueueDaemon extends Daemon {
private static final ReferenceQueueDaemon INSTANCE = new ReferenceQueueDaemon();
ReferenceQueueDaemon() {
super("ReferenceQueueDaemon");
}
@Override public void runInternal() {
while (isRunning()) {
Reference<?> list;
try {
synchronized (ReferenceQueue.class) {
while (ReferenceQueue.unenqueued == null) {
ReferenceQueue.class.wait();
}
list = ReferenceQueue.unenqueued;
ReferenceQueue.unenqueued = null;
}
} catch (InterruptedException e) {
continue;
} catch (OutOfMemoryError e) {
continue;
}
ReferenceQueue.enqueuePending(list);
}
}
}
private static class FinalizerDaemon extends Daemon {
private static final FinalizerDaemon INSTANCE = new FinalizerDaemon();
private final ReferenceQueue<Object> queue = FinalizerReference.queue;
private final AtomicInteger progressCounter = new AtomicInteger(0);
// Object (not reference!) being finalized. Accesses may race!
private Object finalizingObject = null;
FinalizerDaemon() {
super("FinalizerDaemon");
}
@Override public void runInternal() {
// This loop may be performance critical, since we need to keep up with mutator
// generation of finalizable objects.
// We minimize the amount of work we do per finalizable object. For example, we avoid
// reading the current time here, since that involves a kernel call per object. We
// limit fast path communication with FinalizerWatchDogDaemon to what's unavoidable: A
// non-volatile store to communicate the current finalizable object, e.g. for
// reporting, and a release store (lazySet) to a counter.
// We do stop the FinalizerWatchDogDaemon if we have nothing to do for a
// potentially extended period. This prevents the device from waking up regularly
// during idle times.
// Local copy of progressCounter; saves a fence per increment on ARM and MIPS.
int localProgressCounter = progressCounter.get();
while (isRunning()) {
try {
// Use non-blocking poll to avoid FinalizerWatchdogDaemon communication
// when busy.
FinalizerReference<?> finalizingReference = (FinalizerReference<?>)queue.poll();
if (finalizingReference != null) {
finalizingObject = finalizingReference.get();
progressCounter.lazySet(++localProgressCounter);
} else {
finalizingObject = null;
progressCounter.lazySet(++localProgressCounter);
// Slow path; block.
FinalizerWatchdogDaemon.INSTANCE.goToSleep();
finalizingReference = (FinalizerReference<?>)queue.remove();
finalizingObject = finalizingReference.get();
progressCounter.set(++localProgressCounter);
FinalizerWatchdogDaemon.INSTANCE.wakeUp();
}
doFinalize(finalizingReference);
} catch (InterruptedException ignored) {
} catch (OutOfMemoryError ignored) {
}
}
}
@FindBugsSuppressWarnings("FI_EXPLICIT_INVOCATION")
private void doFinalize(FinalizerReference<?> reference) {
FinalizerReference.remove(reference);
Object object = reference.get();
reference.clear();
try {
object.finalize();
} catch (Throwable ex) {
// The RI silently swallows these, but Android has always logged.
System.logE("Uncaught exception thrown by finalizer", ex);
} finally {
// Done finalizing, stop holding the object as live.
finalizingObject = null;
}
}
}
/**
* The watchdog exits the VM if the finalizer ever gets stuck. We consider
* the finalizer to be stuck if it spends more than MAX_FINALIZATION_MILLIS
* on one instance.
*/
private static class FinalizerWatchdogDaemon extends Daemon {
private static final FinalizerWatchdogDaemon INSTANCE = new FinalizerWatchdogDaemon();
private boolean needToWork = true; // Only accessed in synchronized methods.
FinalizerWatchdogDaemon() {
super("FinalizerWatchdogDaemon");
}
@Override public void runInternal() {
while (isRunning()) {
if (!sleepUntilNeeded()) {
// We have been interrupted, need to see if this daemon has been stopped.
continue;
}
final Object finalizing = waitForFinalization();
if (finalizing != null && !VMRuntime.getRuntime().isDebuggerActive()) {
finalizerTimedOut(finalizing);
break;
}
}
}
/**
* Wait until something is ready to be finalized.
* Return false if we have been interrupted
* See also http://code.google.com/p/android/issues/detail?id=22778.
*/
private synchronized boolean sleepUntilNeeded() {
while (!needToWork) {
try {
wait();
} catch (InterruptedException e) {
// Daemon.stop may have interrupted us.
return false;
} catch (OutOfMemoryError e) {
return false;
}
}
return true;
}
/**
* Notify daemon that it's OK to sleep until notified that something is ready to be
* finalized.
*/
private synchronized void goToSleep() {
needToWork = false;
}
/**
* Notify daemon that there is something ready to be finalized.
*/
private synchronized void wakeUp() {
needToWork = true;
notify();
}
private synchronized boolean getNeedToWork() {
return needToWork;
}
/**
* Sleep for the given number of nanoseconds.
* @return false if we were interrupted.
*/
private boolean sleepFor(long durationNanos) {
long startNanos = System.nanoTime();
while (true) {
long elapsedNanos = System.nanoTime() - startNanos;
long sleepNanos = durationNanos - elapsedNanos;
long sleepMills = sleepNanos / NANOS_PER_MILLI;
if (sleepMills <= 0) {
return true;
}
try {
Thread.sleep(sleepMills);
} catch (InterruptedException e) {
if (!isRunning()) {
return false;
}
} catch (OutOfMemoryError ignored) {
if (!isRunning()) {
return false;
}
}
}
}
/**
* Return an object that took too long to finalize or return null.
* Wait MAX_FINALIZE_NANOS. If the FinalizerDaemon took essentially the whole time
* processing a single reference, return that reference. Otherwise return null.
*/
private Object waitForFinalization() {
long startCount = FinalizerDaemon.INSTANCE.progressCounter.get();
// Avoid remembering object being finalized, so as not to keep it alive.
if (!sleepFor(MAX_FINALIZE_NANOS)) {
// Don't report possibly spurious timeout if we are interrupted.
return null;
}
if (getNeedToWork() && FinalizerDaemon.INSTANCE.progressCounter.get() == startCount) {
// We assume that only remove() and doFinalize() may take time comparable to
// MAX_FINALIZE_NANOS.
// We observed neither the effect of the gotoSleep() nor the increment preceding a
// later wakeUp. Any remove() call by the FinalizerDaemon during our sleep
// interval must have been followed by a wakeUp call before we checked needToWork.
// But then we would have seen the counter increment. Thus there cannot have
// been such a remove() call.
// The FinalizerDaemon must not have progressed (from either the beginning or the
// last progressCounter increment) to either the next increment or gotoSleep()
// call. Thus we must have taken essentially the whole MAX_FINALIZE_NANOS in a
// single doFinalize() call. Thus it's OK to time out. finalizingObject was set
// just before the counter increment, which preceded the doFinalize call. Thus we
// are guaranteed to get the correct finalizing value below, unless doFinalize()
// just finished as we were timing out, in which case we may get null or a later
// one. In this last case, we are very likely to discard it below.
Object finalizing = FinalizerDaemon.INSTANCE.finalizingObject;
sleepFor(NANOS_PER_SECOND / 2);
// Recheck to make it even less likely we report the wrong finalizing object in
// the case which a very slow finalization just finished as we were timing out.
if (getNeedToWork()
&& FinalizerDaemon.INSTANCE.progressCounter.get() == startCount) {
return finalizing;
}
}
return null;
}
private static void finalizerTimedOut(Object object) {
// The current object has exceeded the finalization deadline; abort!
String message = object.getClass().getName() + ".finalize() timed out after "
+ (MAX_FINALIZE_NANOS / NANOS_PER_SECOND) + " seconds";
Exception syntheticException = new TimeoutException(message);
// We use the stack from where finalize() was running to show where it was stuck.
syntheticException.setStackTrace(FinalizerDaemon.INSTANCE.getStackTrace());
// Send SIGQUIT to get native stack traces.
try {
Os.kill(Os.getpid(), OsConstants.SIGQUIT);
// Sleep a few seconds to let the stack traces print.
Thread.sleep(5000);
} catch (Exception e) {
System.logE("failed to send SIGQUIT", e);
} catch (OutOfMemoryError ignored) {
// May occur while trying to allocate the exception.
}
// Ideally, we'd want to do this if this Thread had no handler to dispatch to.
// Unfortunately, it's extremely to messy to query whether a given Thread has *some*
// handler to dispatch to, either via a handler set on itself, via its ThreadGroup
// object or via the defaultUncaughtExceptionHandler.
//
// As an approximation, we log by hand an exit if there's no pre-exception handler nor
// a default uncaught exception handler.
//
// Note that this condition will only ever be hit by ART host tests and standalone
// dalvikvm invocations. All zygote forked process *will* have a pre-handler set
// in RuntimeInit and they cannot subsequently override it.
if (Thread.getUncaughtExceptionPreHandler() == null &&
Thread.getDefaultUncaughtExceptionHandler() == null) {
// If we have no handler, log and exit.
System.logE(message, syntheticException);
System.exit(2);
}
// Otherwise call the handler to do crash reporting.
// We don't just throw because we're not the thread that
// timed out; we're the thread that detected it.
Thread.currentThread().dispatchUncaughtException(syntheticException);
}
}
// Adds a heap trim task to the heap event processor, not called from java. Left for
// compatibility purposes due to reflection.
public static void requestHeapTrim() {
VMRuntime.getRuntime().requestHeapTrim();
}
// Adds a concurrent GC request task ot the heap event processor, not called from java. Left
// for compatibility purposes due to reflection.
public static void requestGC() {
VMRuntime.getRuntime().requestConcurrentGC();
}
private static class HeapTaskDaemon extends Daemon {
private static final HeapTaskDaemon INSTANCE = new HeapTaskDaemon();
HeapTaskDaemon() {
super("HeapTaskDaemon");
}
// Overrides the Daemon.interupt method which is called from Daemons.stop.
public synchronized void interrupt(Thread thread) {
VMRuntime.getRuntime().stopHeapTaskProcessor();
}
@Override public void runInternal() {
synchronized (this) {
if (isRunning()) {
// Needs to be synchronized or else we there is a race condition where we start
// the thread, call stopHeapTaskProcessor before we start the heap task
// processor, resulting in a deadlock since startHeapTaskProcessor restarts it
// while the other thread is waiting in Daemons.stop().
VMRuntime.getRuntime().startHeapTaskProcessor();
}
}
// This runs tasks until we are stopped and there is no more pending task.
VMRuntime.getRuntime().runHeapTasks();
}
}
}