| /* |
| * Copyright (C) 2007 The Guava Authors |
| * |
| * 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. |
| */ |
| |
| /** |
| * Some portions of this class have been modified to make it functional in this |
| * package. |
| */ |
| package org.apache.hadoop.ozone.container.common.volume; |
| |
| import com.google.common.annotations.Beta; |
| import com.google.common.annotations.GwtCompatible; |
| import com.google.common.base.Preconditions; |
| import static com.google.common.base.Preconditions.checkNotNull; |
| import com.google.common.util.concurrent.Futures; |
| import com.google.common.util.concurrent.ListeningExecutorService; |
| import com.google.common.util.concurrent.ListenableFuture; |
| import com.google.common.util.concurrent.SettableFuture; |
| import com.google.common.util.concurrent.Uninterruptibles; |
| import edu.umd.cs.findbugs.annotations.SuppressFBWarnings; |
| import static java.util.concurrent.atomic.AtomicReferenceFieldUpdater |
| .newUpdater; |
| |
| import javax.annotation.Nullable; |
| import java.security.AccessController; |
| import java.security.PrivilegedActionException; |
| import java.security.PrivilegedExceptionAction; |
| import java.util.concurrent.CancellationException; |
| import java.util.concurrent.ExecutionException; |
| import java.util.concurrent.Executor; |
| import java.util.concurrent.Future; |
| import java.util.concurrent.TimeUnit; |
| import java.util.concurrent.TimeoutException; |
| import java.util.concurrent.atomic.AtomicReferenceFieldUpdater; |
| import java.util.concurrent.ThreadPoolExecutor.CallerRunsPolicy; |
| import java.util.concurrent.locks.LockSupport; |
| import java.util.logging.Level; |
| import java.util.logging.Logger; |
| |
| /** |
| * An abstract implementation of {@link ListenableFuture}, intended for |
| * advanced users only. More common ways to create a {@code ListenableFuture} |
| * include instantiating a {@link SettableFuture}, submitting a task to a |
| * {@link ListeningExecutorService}, and deriving a {@code Future} from an |
| * existing one, typically using methods like {@link Futures#transform |
| * (ListenableFuture, com.google.common.base.Function) Futures.transform} |
| * and its overloaded versions. |
| * <p> |
| * <p>This class implements all methods in {@code ListenableFuture}. |
| * Subclasses should provide a way to set the result of the computation |
| * through the protected methods {@link #set(Object)}, |
| * {@link #setFuture(ListenableFuture)} and {@link #setException(Throwable)}. |
| * Subclasses may also override {@link #interruptTask()}, which will be |
| * invoked automatically if a call to {@link #cancel(boolean) cancel(true)} |
| * succeeds in canceling the future. Subclasses should rarely override other |
| * methods. |
| */ |
| |
| @GwtCompatible(emulated = true) |
| public abstract class AbstractFuture<V> implements ListenableFuture<V> { |
| // NOTE: Whenever both tests are cheap and functional, it's faster to use &, |
| // | instead of &&, || |
| |
| private static final boolean GENERATE_CANCELLATION_CAUSES = |
| Boolean.parseBoolean( |
| System.getProperty("guava.concurrent.generate_cancellation_cause", |
| "false")); |
| |
| /** |
| * A less abstract subclass of AbstractFuture. This can be used to optimize |
| * setFuture by ensuring that {@link #get} calls exactly the implementation |
| * of {@link AbstractFuture#get}. |
| */ |
| abstract static class TrustedFuture<V> extends AbstractFuture<V> { |
| @Override |
| public final V get() throws InterruptedException, ExecutionException { |
| return super.get(); |
| } |
| |
| @Override |
| public final V get(long timeout, TimeUnit unit) |
| throws InterruptedException, ExecutionException, TimeoutException { |
| return super.get(timeout, unit); |
| } |
| |
| @Override |
| public final boolean isDone() { |
| return super.isDone(); |
| } |
| |
| @Override |
| public final boolean isCancelled() { |
| return super.isCancelled(); |
| } |
| |
| @Override |
| public final void addListener(Runnable listener, Executor executor) { |
| super.addListener(listener, executor); |
| } |
| |
| @Override |
| public final boolean cancel(boolean mayInterruptIfRunning) { |
| return super.cancel(mayInterruptIfRunning); |
| } |
| } |
| |
| // Logger to log exceptions caught when running listeners. |
| private static final Logger LOG = Logger |
| .getLogger(AbstractFuture.class.getName()); |
| |
| // A heuristic for timed gets. If the remaining timeout is less than this, |
| // spin instead of |
| // blocking. This value is what AbstractQueuedSynchronizer uses. |
| private static final long SPIN_THRESHOLD_NANOS = 1000L; |
| |
| private static final AtomicHelper ATOMIC_HELPER; |
| |
| static { |
| AtomicHelper helper; |
| |
| try { |
| helper = new UnsafeAtomicHelper(); |
| } catch (Throwable unsafeFailure) { |
| // catch absolutely everything and fall through to our 'SafeAtomicHelper' |
| // The access control checks that ARFU does means the caller class has |
| // to be AbstractFuture |
| // instead of SafeAtomicHelper, so we annoyingly define these here |
| try { |
| helper = |
| new SafeAtomicHelper( |
| newUpdater(Waiter.class, Thread.class, "thread"), |
| newUpdater(Waiter.class, Waiter.class, "next"), |
| newUpdater(AbstractFuture.class, Waiter.class, "waiters"), |
| newUpdater(AbstractFuture.class, Listener.class, "listeners"), |
| newUpdater(AbstractFuture.class, Object.class, "value")); |
| } catch (Throwable atomicReferenceFieldUpdaterFailure) { |
| // Some Android 5.0.x Samsung devices have bugs in JDK reflection APIs |
| // that cause getDeclaredField to throw a NoSuchFieldException when |
| // the field is definitely there. |
| // For these users fallback to a suboptimal implementation, based on |
| // synchronized. This will be a definite performance hit to those users. |
| LOG.log(Level.SEVERE, "UnsafeAtomicHelper is broken!", unsafeFailure); |
| LOG.log( |
| Level.SEVERE, "SafeAtomicHelper is broken!", |
| atomicReferenceFieldUpdaterFailure); |
| helper = new SynchronizedHelper(); |
| } |
| } |
| ATOMIC_HELPER = helper; |
| |
| // Prevent rare disastrous classloading in first call to LockSupport.park. |
| // See: https://bugs.openjdk.java.net/browse/JDK-8074773 |
| @SuppressWarnings("unused") |
| @SuppressFBWarnings |
| Class<?> ensureLoaded = LockSupport.class; |
| } |
| |
| /** |
| * Waiter links form a Treiber stack, in the {@link #waiters} field. |
| */ |
| @SuppressWarnings("visibilitymodifier") |
| private static final class Waiter { |
| static final Waiter TOMBSTONE = new Waiter(false /* ignored param */); |
| |
| @Nullable volatile Thread thread; |
| @Nullable volatile Waiter next; |
| |
| /** |
| * Constructor for the TOMBSTONE, avoids use of ATOMIC_HELPER in case this |
| * class is loaded before the ATOMIC_HELPER. Apparently this is possible |
| * on some android platforms. |
| */ |
| Waiter(boolean unused) { |
| } |
| |
| Waiter() { |
| // avoid volatile write, write is made visible by subsequent CAS on |
| // waiters field |
| ATOMIC_HELPER.putThread(this, Thread.currentThread()); |
| } |
| |
| // non-volatile write to the next field. Should be made visible by |
| // subsequent CAS on waiters field. |
| void setNext(Waiter next) { |
| ATOMIC_HELPER.putNext(this, next); |
| } |
| |
| void unpark() { |
| // This is racy with removeWaiter. The consequence of the race is that |
| // we may spuriously call unpark even though the thread has already |
| // removed itself from the list. But even if we did use a CAS, that |
| // race would still exist (it would just be ever so slightly smaller). |
| Thread w = thread; |
| if (w != null) { |
| thread = null; |
| LockSupport.unpark(w); |
| } |
| } |
| } |
| |
| /** |
| * Marks the given node as 'deleted' (null waiter) and then scans the list |
| * to unlink all deleted nodes. This is an O(n) operation in the common |
| * case (and O(n^2) in the worst), but we are saved by two things. |
| * <ul> |
| * <li>This is only called when a waiting thread times out or is |
| * interrupted. Both of which should be rare. |
| * <li>The waiters list should be very short. |
| * </ul> |
| */ |
| private void removeWaiter(Waiter node) { |
| node.thread = null; // mark as 'deleted' |
| restart: |
| while (true) { |
| Waiter pred = null; |
| Waiter curr = waiters; |
| if (curr == Waiter.TOMBSTONE) { |
| return; // give up if someone is calling complete |
| } |
| Waiter succ; |
| while (curr != null) { |
| succ = curr.next; |
| if (curr.thread != null) { // we aren't unlinking this node, update |
| // pred. |
| pred = curr; |
| } else if (pred != null) { // We are unlinking this node and it has a |
| // predecessor. |
| pred.next = succ; |
| if (pred.thread == null) { // We raced with another node that |
| // unlinked pred. Restart. |
| continue restart; |
| } |
| } else if (!ATOMIC_HELPER |
| .casWaiters(this, curr, succ)) { // We are unlinking head |
| continue restart; // We raced with an add or complete |
| } |
| curr = succ; |
| } |
| break; |
| } |
| } |
| |
| /** |
| * Listeners also form a stack through the {@link #listeners} field. |
| */ |
| @SuppressWarnings("visibilitymodifier") |
| private static final class Listener { |
| static final Listener TOMBSTONE = new Listener(null, null); |
| final Runnable task; |
| final Executor executor; |
| |
| // writes to next are made visible by subsequent CAS's on the listeners |
| // field |
| @Nullable Listener next; |
| |
| Listener(Runnable task, Executor executor) { |
| this.task = task; |
| this.executor = executor; |
| } |
| } |
| |
| /** |
| * A special value to represent {@code null}. |
| */ |
| private static final Object NULL = new Object(); |
| |
| /** |
| * A special value to represent failure, when {@link #setException} is |
| * called successfully. |
| */ |
| @SuppressWarnings("visibilitymodifier") |
| private static final class Failure { |
| static final Failure FALLBACK_INSTANCE = |
| new Failure( |
| new Throwable("Failure occurred while trying to finish a future" + |
| ".") { |
| @Override |
| public synchronized Throwable fillInStackTrace() { |
| return this; // no stack trace |
| } |
| }); |
| final Throwable exception; |
| |
| Failure(Throwable exception) { |
| this.exception = checkNotNull(exception); |
| } |
| } |
| |
| /** |
| * A special value to represent cancellation and the 'wasInterrupted' bit. |
| */ |
| @SuppressWarnings("visibilitymodifier") |
| private static final class Cancellation { |
| final boolean wasInterrupted; |
| @Nullable final Throwable cause; |
| |
| Cancellation(boolean wasInterrupted, @Nullable Throwable cause) { |
| this.wasInterrupted = wasInterrupted; |
| this.cause = cause; |
| } |
| } |
| |
| /** |
| * A special value that encodes the 'setFuture' state. |
| */ |
| @SuppressWarnings("visibilitymodifier") |
| private static final class SetFuture<V> implements Runnable { |
| final AbstractFuture<V> owner; |
| final ListenableFuture<? extends V> future; |
| |
| SetFuture(AbstractFuture<V> owner, ListenableFuture<? extends V> future) { |
| this.owner = owner; |
| this.future = future; |
| } |
| |
| @Override |
| public void run() { |
| if (owner.value != this) { |
| // nothing to do, we must have been cancelled, don't bother inspecting |
| // the future. |
| return; |
| } |
| Object valueToSet = getFutureValue(future); |
| if (ATOMIC_HELPER.casValue(owner, this, valueToSet)) { |
| complete(owner); |
| } |
| } |
| } |
| |
| /** |
| * This field encodes the current state of the future. |
| * <p> |
| * <p>The valid values are: |
| * <ul> |
| * <li>{@code null} initial state, nothing has happened. |
| * <li>{@link Cancellation} terminal state, {@code cancel} was called. |
| * <li>{@link Failure} terminal state, {@code setException} was called. |
| * <li>{@link SetFuture} intermediate state, {@code setFuture} was called. |
| * <li>{@link #NULL} terminal state, {@code set(null)} was called. |
| * <li>Any other non-null value, terminal state, {@code set} was called with |
| * a non-null argument. |
| * </ul> |
| */ |
| private volatile Object value; |
| |
| /** |
| * All listeners. |
| */ |
| private volatile Listener listeners; |
| |
| /** |
| * All waiting threads. |
| */ |
| private volatile Waiter waiters; |
| |
| /** |
| * Constructor for use by subclasses. |
| */ |
| protected AbstractFuture() { |
| } |
| |
| // Gets and Timed Gets |
| // |
| // * Be responsive to interruption |
| // * Don't create Waiter nodes if you aren't going to park, this helps |
| // reduce contention on the waiters field. |
| // * Future completion is defined by when #value becomes non-null/non |
| // SetFuture |
| // * Future completion can be observed if the waiters field contains a |
| // TOMBSTONE |
| |
| // Timed Get |
| // There are a few design constraints to consider |
| // * We want to be responsive to small timeouts, unpark() has non trivial |
| // latency overheads (I have observed 12 micros on 64 bit linux systems to |
| // wake up a parked thread). So if the timeout is small we shouldn't park(). |
| // This needs to be traded off with the cpu overhead of spinning, so we use |
| // SPIN_THRESHOLD_NANOS which is what AbstractQueuedSynchronizer uses for |
| // similar purposes. |
| // * We want to behave reasonably for timeouts of 0 |
| // * We are more responsive to completion than timeouts. This is because |
| // parkNanos depends on system scheduling and as such we could either miss |
| // our deadline, or unpark() could be delayed so that it looks like we |
| // timed out even though we didn't. For comparison FutureTask respects |
| // completion preferably and AQS is non-deterministic (depends on where in |
| // the queue the waiter is). If we wanted to be strict about it, we could |
| // store the unpark() time in the Waiter node and we could use that to make |
| // a decision about whether or not we timed out prior to being unparked. |
| |
| /* |
| * Improve the documentation of when InterruptedException is thrown. Our |
| * behavior matches the JDK's, but the JDK's documentation is misleading. |
| */ |
| |
| /** |
| * {@inheritDoc} |
| * <p> |
| * <p>The default {@link AbstractFuture} implementation throws {@code |
| * InterruptedException} if the current thread is interrupted before or |
| * during the call, even if the value is already available. |
| * |
| * @throws InterruptedException if the current thread was interrupted |
| * before or during the call |
| * (optional but recommended). |
| * @throws CancellationException {@inheritDoc} |
| */ |
| @Override |
| public V get(long timeout, TimeUnit unit) |
| throws InterruptedException, TimeoutException, ExecutionException { |
| // NOTE: if timeout < 0, remainingNanos will be < 0 and we will fall into |
| // the while(true) loop at the bottom and throw a timeoutexception. |
| long remainingNanos = unit |
| .toNanos(timeout); // we rely on the implicit null check on unit. |
| if (Thread.interrupted()) { |
| throw new InterruptedException(); |
| } |
| Object localValue = value; |
| if (localValue != null & !(localValue instanceof SetFuture)) { |
| return getDoneValue(localValue); |
| } |
| // we delay calling nanoTime until we know we will need to either park or |
| // spin |
| final long endNanos = remainingNanos > 0 ? System |
| .nanoTime() + remainingNanos : 0; |
| long_wait_loop: |
| if (remainingNanos >= SPIN_THRESHOLD_NANOS) { |
| Waiter oldHead = waiters; |
| if (oldHead != Waiter.TOMBSTONE) { |
| Waiter node = new Waiter(); |
| do { |
| node.setNext(oldHead); |
| if (ATOMIC_HELPER.casWaiters(this, oldHead, node)) { |
| while (true) { |
| LockSupport.parkNanos(this, remainingNanos); |
| // Check interruption first, if we woke up due to interruption |
| // we need to honor that. |
| if (Thread.interrupted()) { |
| removeWaiter(node); |
| throw new InterruptedException(); |
| } |
| |
| // Otherwise re-read and check doneness. If we loop then it must |
| // have been a spurious wakeup |
| localValue = value; |
| if (localValue != null & !(localValue instanceof SetFuture)) { |
| return getDoneValue(localValue); |
| } |
| |
| // timed out? |
| remainingNanos = endNanos - System.nanoTime(); |
| if (remainingNanos < SPIN_THRESHOLD_NANOS) { |
| // Remove the waiter, one way or another we are done parking |
| // this thread. |
| removeWaiter(node); |
| break long_wait_loop; // jump down to the busy wait loop |
| } |
| } |
| } |
| oldHead = waiters; // re-read and loop. |
| } while (oldHead != Waiter.TOMBSTONE); |
| } |
| // re-read value, if we get here then we must have observed a TOMBSTONE |
| // while trying to add a waiter. |
| return getDoneValue(value); |
| } |
| // If we get here then we have remainingNanos < SPIN_THRESHOLD_NANOS and |
| // there is no node on the waiters list |
| while (remainingNanos > 0) { |
| localValue = value; |
| if (localValue != null & !(localValue instanceof SetFuture)) { |
| return getDoneValue(localValue); |
| } |
| if (Thread.interrupted()) { |
| throw new InterruptedException(); |
| } |
| remainingNanos = endNanos - System.nanoTime(); |
| } |
| throw new TimeoutException(); |
| } |
| |
| /* |
| * Improve the documentation of when InterruptedException is thrown. Our |
| * behavior matches the JDK's, but the JDK's documentation is misleading. |
| */ |
| |
| /** |
| * {@inheritDoc} |
| * <p> |
| * <p>The default {@link AbstractFuture} implementation throws {@code |
| * InterruptedException} if the current thread is interrupted before or |
| * during the call, even if the value is already available. |
| * |
| * @throws InterruptedException if the current thread was interrupted |
| * before or during the call |
| * (optional but recommended). |
| * @throws CancellationException {@inheritDoc} |
| */ |
| @Override |
| public V get() throws InterruptedException, ExecutionException { |
| if (Thread.interrupted()) { |
| throw new InterruptedException(); |
| } |
| Object localValue = value; |
| if (localValue != null & !(localValue instanceof SetFuture)) { |
| return getDoneValue(localValue); |
| } |
| Waiter oldHead = waiters; |
| if (oldHead != Waiter.TOMBSTONE) { |
| Waiter node = new Waiter(); |
| do { |
| node.setNext(oldHead); |
| if (ATOMIC_HELPER.casWaiters(this, oldHead, node)) { |
| // we are on the stack, now wait for completion. |
| while (true) { |
| LockSupport.park(this); |
| // Check interruption first, if we woke up due to interruption we |
| // need to honor that. |
| if (Thread.interrupted()) { |
| removeWaiter(node); |
| throw new InterruptedException(); |
| } |
| // Otherwise re-read and check doneness. If we loop then it must |
| // have been a spurious wakeup |
| localValue = value; |
| if (localValue != null & !(localValue instanceof SetFuture)) { |
| return getDoneValue(localValue); |
| } |
| } |
| } |
| oldHead = waiters; // re-read and loop. |
| } while (oldHead != Waiter.TOMBSTONE); |
| } |
| // re-read value, if we get here then we must have observed a TOMBSTONE |
| // while trying to add a waiter. |
| return getDoneValue(value); |
| } |
| |
| /** |
| * Unboxes {@code obj}. Assumes that obj is not {@code null} or a |
| * {@link SetFuture}. |
| */ |
| private V getDoneValue(Object obj) throws ExecutionException { |
| // While this seems like it might be too branch-y, simple benchmarking |
| // proves it to be unmeasurable (comparing done AbstractFutures with |
| // immediateFuture) |
| if (obj instanceof Cancellation) { |
| throw cancellationExceptionWithCause( |
| "Task was cancelled.", ((Cancellation) obj).cause); |
| } else if (obj instanceof Failure) { |
| throw new ExecutionException(((Failure) obj).exception); |
| } else if (obj == NULL) { |
| return null; |
| } else { |
| @SuppressWarnings("unchecked") // this is the only other option |
| V asV = (V) obj; |
| return asV; |
| } |
| } |
| |
| @Override |
| public boolean isDone() { |
| final Object localValue = value; |
| return localValue != null & !(localValue instanceof SetFuture); |
| } |
| |
| @Override |
| public boolean isCancelled() { |
| final Object localValue = value; |
| return localValue instanceof Cancellation; |
| } |
| |
| /** |
| * {@inheritDoc} |
| * <p> |
| * <p>If a cancellation attempt succeeds on a {@code Future} that had |
| * previously been {@linkplain#setFuture set asynchronously}, then the |
| * cancellation will also be propagated to the delegate {@code Future} that |
| * was supplied in the {@code setFuture} call. |
| */ |
| @Override |
| public boolean cancel(boolean mayInterruptIfRunning) { |
| Object localValue = value; |
| boolean rValue = false; |
| if (localValue == null | localValue instanceof SetFuture) { |
| // Try to delay allocating the exception. At this point we may still |
| // lose the CAS, but it is certainly less likely. |
| Throwable cause = |
| GENERATE_CANCELLATION_CAUSES |
| ? new CancellationException("Future.cancel() was called.") |
| : null; |
| Object valueToSet = new Cancellation(mayInterruptIfRunning, cause); |
| AbstractFuture<?> abstractFuture = this; |
| while (true) { |
| if (ATOMIC_HELPER.casValue(abstractFuture, localValue, valueToSet)) { |
| rValue = true; |
| // We call interuptTask before calling complete(), which is |
| // consistent with FutureTask |
| if (mayInterruptIfRunning) { |
| abstractFuture.interruptTask(); |
| } |
| complete(abstractFuture); |
| if (localValue instanceof SetFuture) { |
| // propagate cancellation to the future set in setfuture, this is |
| // racy, and we don't care if we are successful or not. |
| ListenableFuture<?> futureToPropagateTo = ((SetFuture) localValue) |
| .future; |
| if (futureToPropagateTo instanceof TrustedFuture) { |
| // If the future is a TrustedFuture then we specifically avoid |
| // calling cancel() this has 2 benefits |
| // 1. for long chains of futures strung together with setFuture |
| // we consume less stack |
| // 2. we avoid allocating Cancellation objects at every level of |
| // the cancellation chain |
| // We can only do this for TrustedFuture, because |
| // TrustedFuture.cancel is final and does nothing but delegate |
| // to this method. |
| AbstractFuture<?> trusted = (AbstractFuture<?>) |
| futureToPropagateTo; |
| localValue = trusted.value; |
| if (localValue == null | localValue instanceof SetFuture) { |
| abstractFuture = trusted; |
| continue; // loop back up and try to complete the new future |
| } |
| } else { |
| // not a TrustedFuture, call cancel directly. |
| futureToPropagateTo.cancel(mayInterruptIfRunning); |
| } |
| } |
| break; |
| } |
| // obj changed, reread |
| localValue = abstractFuture.value; |
| if (!(localValue instanceof SetFuture)) { |
| // obj cannot be null at this point, because value can only change |
| // from null to non-null. So if value changed (and it did since we |
| // lost the CAS), then it cannot be null and since it isn't a |
| // SetFuture, then the future must be done and we should exit the loop |
| break; |
| } |
| } |
| } |
| return rValue; |
| } |
| |
| /** |
| * Subclasses can override this method to implement interruption of the |
| * future's computation. The method is invoked automatically by a |
| * successful call to {@link #cancel(boolean) cancel(true)}. |
| * <p> |
| * <p>The default implementation does nothing. |
| * |
| * @since 10.0 |
| */ |
| protected void interruptTask() { |
| } |
| |
| /** |
| * Returns true if this future was cancelled with {@code |
| * mayInterruptIfRunning} set to {@code true}. |
| * |
| * @since 14.0 |
| */ |
| protected final boolean wasInterrupted() { |
| final Object localValue = value; |
| return (localValue instanceof Cancellation) && ((Cancellation) localValue) |
| .wasInterrupted; |
| } |
| |
| /** |
| * {@inheritDoc} |
| * |
| * @since 10.0 |
| */ |
| @Override |
| public void addListener(Runnable listener, Executor executor) { |
| checkNotNull(listener, "Runnable was null."); |
| checkNotNull(executor, "Executor was null."); |
| Listener oldHead = listeners; |
| if (oldHead != Listener.TOMBSTONE) { |
| Listener newNode = new Listener(listener, executor); |
| do { |
| newNode.next = oldHead; |
| if (ATOMIC_HELPER.casListeners(this, oldHead, newNode)) { |
| return; |
| } |
| oldHead = listeners; // re-read |
| } while (oldHead != Listener.TOMBSTONE); |
| } |
| // If we get here then the Listener TOMBSTONE was set, which means the |
| // future is done, call the listener. |
| executeListener(listener, executor); |
| } |
| |
| /** |
| * Sets the result of this {@code Future} unless this {@code Future} has |
| * already been cancelled or set (including |
| * {@linkplain #setFuture set asynchronously}). When a call to this method |
| * returns, the {@code Future} is guaranteed to be |
| * {@linkplain #isDone done} <b>only if</b> the call was accepted (in which |
| * case it returns {@code true}). If it returns {@code false}, the {@code |
| * Future} may have previously been set asynchronously, in which case its |
| * result may not be known yet. That result, though not yet known, cannot |
| * be overridden by a call to a {@code set*} method, only by a call to |
| * {@link #cancel}. |
| * |
| * @param value the value to be used as the result |
| * @return true if the attempt was accepted, completing the {@code Future} |
| */ |
| protected boolean set(@Nullable V val) { |
| Object valueToSet = value == null ? NULL : val; |
| if (ATOMIC_HELPER.casValue(this, null, valueToSet)) { |
| complete(this); |
| return true; |
| } |
| return false; |
| } |
| |
| /** |
| * Sets the failed result of this {@code Future} unless this {@code Future} |
| * has already been cancelled or set (including |
| * {@linkplain #setFuture set asynchronously}). When a call to this method |
| * returns, the {@code Future} is guaranteed to be |
| * {@linkplain #isDone done} <b>only if</b> the call was accepted (in which |
| * case it returns {@code true}). If it returns {@code false}, the |
| * {@code Future} may have previously been set asynchronously, in which case |
| * its result may not be known yet. That result, though not yet known, |
| * cannot be overridden by a call to a {@code set*} method, only by a call |
| * to {@link #cancel}. |
| * |
| * @param throwable the exception to be used as the failed result |
| * @return true if the attempt was accepted, completing the {@code Future} |
| */ |
| protected boolean setException(Throwable throwable) { |
| Object valueToSet = new Failure(checkNotNull(throwable)); |
| if (ATOMIC_HELPER.casValue(this, null, valueToSet)) { |
| complete(this); |
| return true; |
| } |
| return false; |
| } |
| |
| /** |
| * Sets the result of this {@code Future} to match the supplied input |
| * {@code Future} once the supplied {@code Future} is done, unless this |
| * {@code Future} has already been cancelled or set (including "set |
| * asynchronously," defined below). |
| * <p> |
| * <p>If the supplied future is {@linkplain #isDone done} when this method |
| * is called and the call is accepted, then this future is guaranteed to |
| * have been completed with the supplied future by the time this method |
| * returns. If the supplied future is not done and the call is accepted, then |
| * the future will be <i>set asynchronously</i>. Note that such a result, |
| * though not yet known, cannot be overridden by a call to a {@code set*} |
| * method, only by a call to {@link #cancel}. |
| * <p> |
| * <p>If the call {@code setFuture(delegate)} is accepted and this {@code |
| * Future} is later cancelled, cancellation will be propagated to {@code |
| * delegate}. Additionally, any call to {@code setFuture} after any |
| * cancellation will propagate cancellation to the supplied {@code Future}. |
| * |
| * @param future the future to delegate to |
| * @return true if the attempt was accepted, indicating that the {@code |
| * Future} was not previously cancelled or set. |
| * @since 19.0 |
| */ |
| @Beta |
| @SuppressWarnings("deadstore") |
| protected boolean setFuture(ListenableFuture<? extends V> future) { |
| checkNotNull(future); |
| Object localValue = value; |
| if (localValue == null) { |
| if (future.isDone()) { |
| Object val = getFutureValue(future); |
| if (ATOMIC_HELPER.casValue(this, null, val)) { |
| complete(this); |
| return true; |
| } |
| return false; |
| } |
| SetFuture valueToSet = new SetFuture<V>(this, future); |
| if (ATOMIC_HELPER.casValue(this, null, valueToSet)) { |
| // the listener is responsible for calling completeWithFuture, |
| // directExecutor is appropriate since all we are doing is unpacking |
| // a completed future which should be fast. |
| try { |
| future.addListener(valueToSet, directExecutor()); |
| } catch (Throwable t) { |
| // addListener has thrown an exception! SetFuture.run can't throw |
| // any exceptions so this must have been caused by addListener |
| // itself. The most likely explanation is a misconfigured mock. Try |
| // to switch to Failure. |
| Failure failure; |
| try { |
| failure = new Failure(t); |
| } catch (Throwable oomMostLikely) { |
| failure = Failure.FALLBACK_INSTANCE; |
| } |
| // Note: The only way this CAS could fail is if cancel() has raced |
| // with us. That is ok. |
| boolean unused = ATOMIC_HELPER.casValue(this, valueToSet, failure); |
| } |
| return true; |
| } |
| localValue = value; // we lost the cas, fall through and maybe cancel |
| } |
| // The future has already been set to something. If it is cancellation we |
| // should cancel the incoming future. |
| if (localValue instanceof Cancellation) { |
| // we don't care if it fails, this is best-effort. |
| future.cancel(((Cancellation) localValue).wasInterrupted); |
| } |
| return false; |
| } |
| |
| /** |
| * Returns a value, suitable for storing in the {@link #value} field. From |
| * the given future, which is assumed to be done. |
| * <p> |
| * <p>This is approximately the inverse of {@link #getDoneValue(Object)} |
| */ |
| private static Object getFutureValue(ListenableFuture<?> future) { |
| Object valueToSet; |
| if (future instanceof TrustedFuture) { |
| // Break encapsulation for TrustedFuture instances since we know that |
| // subclasses cannot override .get() (since it is final) and therefore |
| // this is equivalent to calling .get() and unpacking the exceptions |
| // like we do below (just much faster because it is a single field read |
| // instead of a read, several branches and possibly creating exceptions). |
| return ((AbstractFuture<?>) future).value; |
| } else { |
| // Otherwise calculate valueToSet by calling .get() |
| try { |
| Object v = getDone(future); |
| valueToSet = v == null ? NULL : v; |
| } catch (ExecutionException exception) { |
| valueToSet = new Failure(exception.getCause()); |
| } catch (CancellationException cancellation) { |
| valueToSet = new Cancellation(false, cancellation); |
| } catch (Throwable t) { |
| valueToSet = new Failure(t); |
| } |
| } |
| return valueToSet; |
| } |
| |
| /** |
| * Unblocks all threads and runs all listeners. |
| */ |
| private static void complete(AbstractFuture<?> future) { |
| Listener next = null; |
| outer: |
| while (true) { |
| future.releaseWaiters(); |
| // We call this before the listeners in order to avoid needing to manage |
| // a separate stack data structure for them. afterDone() should be |
| // generally fast and only used for cleanup work... but in theory can |
| // also be recursive and create StackOverflowErrors |
| future.afterDone(); |
| // push the current set of listeners onto next |
| next = future.clearListeners(next); |
| future = null; |
| while (next != null) { |
| Listener curr = next; |
| next = next.next; |
| Runnable task = curr.task; |
| if (task instanceof SetFuture) { |
| SetFuture<?> setFuture = (SetFuture<?>) task; |
| // We unwind setFuture specifically to avoid StackOverflowErrors in |
| // the case of long chains of SetFutures |
| // Handling this special case is important because there is no way |
| // to pass an executor to setFuture, so a user couldn't break the |
| // chain by doing this themselves. It is also potentially common |
| // if someone writes a recursive Futures.transformAsync transformer. |
| future = setFuture.owner; |
| if (future.value == setFuture) { |
| Object valueToSet = getFutureValue(setFuture.future); |
| if (ATOMIC_HELPER.casValue(future, setFuture, valueToSet)) { |
| continue outer; |
| } |
| } |
| // other wise the future we were trying to set is already done. |
| } else { |
| executeListener(task, curr.executor); |
| } |
| } |
| break; |
| } |
| } |
| |
| public static <V> V getDone(Future<V> future) throws ExecutionException { |
| /* |
| * We throw IllegalStateException, since the call could succeed later. |
| * Perhaps we "should" throw IllegalArgumentException, since the call |
| * could succeed with a different argument. Those exceptions' docs |
| * suggest that either is acceptable. Google's Java Practices page |
| * recommends IllegalArgumentException here, in part to keep its |
| * recommendation simple: Static methods should throw |
| * IllegalStateException only when they use static state. |
| * |
| * |
| * Why do we deviate here? The answer: We want for fluentFuture.getDone() |
| * to throw the same exception as Futures.getDone(fluentFuture). |
| */ |
| Preconditions.checkState(future.isDone(), "Future was expected to be " + |
| "done:" + |
| " %s", future); |
| return Uninterruptibles.getUninterruptibly(future); |
| } |
| |
| /** |
| * Callback method that is called exactly once after the future is completed. |
| * <p> |
| * <p>If {@link #interruptTask} is also run during completion, |
| * {@link #afterDone} runs after it. |
| * <p> |
| * <p>The default implementation of this method in {@code AbstractFuture} |
| * does nothing. This is intended for very lightweight cleanup work, for |
| * example, timing statistics or clearing fields. |
| * If your task does anything heavier consider, just using a listener with |
| * an executor. |
| * |
| * @since 20.0 |
| */ |
| @Beta |
| protected void afterDone() { |
| } |
| |
| /** |
| * If this future has been cancelled (and possibly interrupted), cancels |
| * (and possibly interrupts) the given future (if available). |
| * <p> |
| * <p>This method should be used only when this future is completed. It is |
| * designed to be called from {@code done}. |
| */ |
| final void maybePropagateCancellation(@Nullable Future<?> related) { |
| if (related != null & isCancelled()) { |
| related.cancel(wasInterrupted()); |
| } |
| } |
| |
| /** |
| * Releases all threads in the {@link #waiters} list, and clears the list. |
| */ |
| private void releaseWaiters() { |
| Waiter head; |
| do { |
| head = waiters; |
| } while (!ATOMIC_HELPER.casWaiters(this, head, Waiter.TOMBSTONE)); |
| for (Waiter currentWaiter = head; |
| currentWaiter != null; currentWaiter = currentWaiter.next) { |
| currentWaiter.unpark(); |
| } |
| } |
| |
| /** |
| * Clears the {@link #listeners} list and prepends its contents to {@code |
| * onto}, least recently added first. |
| */ |
| private Listener clearListeners(Listener onto) { |
| // We need to |
| // 1. atomically swap the listeners with TOMBSTONE, this is because |
| // addListener uses that to to synchronize with us |
| // 2. reverse the linked list, because despite our rather clear contract, |
| // people depend on us executing listeners in the order they were added |
| // 3. push all the items onto 'onto' and return the new head of the stack |
| Listener head; |
| do { |
| head = listeners; |
| } while (!ATOMIC_HELPER.casListeners(this, head, Listener.TOMBSTONE)); |
| Listener reversedList = onto; |
| while (head != null) { |
| Listener tmp = head; |
| head = head.next; |
| tmp.next = reversedList; |
| reversedList = tmp; |
| } |
| return reversedList; |
| } |
| |
| /** |
| * Submits the given runnable to the given {@link Executor} catching and |
| * logging all {@linkplain RuntimeException runtime exceptions} thrown by |
| * the executor. |
| */ |
| private static void executeListener(Runnable runnable, Executor executor) { |
| try { |
| executor.execute(runnable); |
| } catch (RuntimeException e) { |
| // Log it and keep going -- bad runnable and/or executor. Don't punish |
| // the other runnables if we're given a bad one. We only catch |
| // RuntimeException because we want Errors to propagate up. |
| LOG.log( |
| Level.SEVERE, |
| "RuntimeException while executing runnable " + runnable + " with " + |
| "executor " + executor, |
| e); |
| } |
| } |
| |
| private abstract static class AtomicHelper { |
| /** |
| * Non volatile write of the thread to the {@link Waiter#thread} field. |
| */ |
| abstract void putThread(Waiter waiter, Thread newValue); |
| |
| /** |
| * Non volatile write of the waiter to the {@link Waiter#next} field. |
| */ |
| abstract void putNext(Waiter waiter, Waiter newValue); |
| |
| /** |
| * Performs a CAS operation on the {@link #waiters} field. |
| */ |
| abstract boolean casWaiters( |
| AbstractFuture<?> future, Waiter expect, |
| Waiter update); |
| |
| /** |
| * Performs a CAS operation on the {@link #listeners} field. |
| */ |
| abstract boolean casListeners( |
| AbstractFuture<?> future, Listener expect, |
| Listener update); |
| |
| /** |
| * Performs a CAS operation on the {@link #value} field. |
| */ |
| abstract boolean casValue( |
| AbstractFuture<?> future, Object expect, Object update); |
| } |
| |
| /** |
| * {@link AtomicHelper} based on {@link sun.misc.Unsafe}. |
| * <p> |
| * <p>Static initialization of this class will fail if the |
| * {@link sun.misc.Unsafe} object cannot be accessed. |
| */ |
| private static final class UnsafeAtomicHelper extends AtomicHelper { |
| static final sun.misc.Unsafe UNSAFE; |
| static final long LISTENERS_OFFSET; |
| static final long WAITERS_OFFSET; |
| static final long VALUE_OFFSET; |
| static final long WAITER_THREAD_OFFSET; |
| static final long WAITER_NEXT_OFFSET; |
| |
| static { |
| sun.misc.Unsafe unsafe = null; |
| try { |
| unsafe = sun.misc.Unsafe.getUnsafe(); |
| } catch (SecurityException tryReflectionInstead) { |
| try { |
| unsafe = |
| AccessController.doPrivileged( |
| new PrivilegedExceptionAction<sun.misc.Unsafe>() { |
| @Override |
| public sun.misc.Unsafe run() throws Exception { |
| Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class; |
| for (java.lang.reflect.Field f : k.getDeclaredFields()) { |
| f.setAccessible(true); |
| Object x = f.get(null); |
| if (k.isInstance(x)) { |
| return k.cast(x); |
| } |
| } |
| throw new NoSuchFieldError("the Unsafe"); |
| } |
| }); |
| } catch (PrivilegedActionException e) { |
| throw new RuntimeException( |
| "Could not initialize intrinsics", e.getCause()); |
| } |
| } |
| try { |
| Class<?> abstractFuture = AbstractFuture.class; |
| WAITERS_OFFSET = unsafe |
| .objectFieldOffset(abstractFuture.getDeclaredField("waiters")); |
| LISTENERS_OFFSET = unsafe |
| .objectFieldOffset(abstractFuture.getDeclaredField("listeners")); |
| VALUE_OFFSET = unsafe |
| .objectFieldOffset(abstractFuture.getDeclaredField("value")); |
| WAITER_THREAD_OFFSET = unsafe |
| .objectFieldOffset(Waiter.class.getDeclaredField("thread")); |
| WAITER_NEXT_OFFSET = unsafe |
| .objectFieldOffset(Waiter.class.getDeclaredField("next")); |
| UNSAFE = unsafe; |
| } catch (Exception e) { |
| throwIfUnchecked(e); |
| throw new RuntimeException(e); |
| } |
| } |
| |
| public static void throwIfUnchecked(Throwable throwable) { |
| checkNotNull(throwable); |
| if (throwable instanceof RuntimeException) { |
| throw (RuntimeException) throwable; |
| } |
| if (throwable instanceof Error) { |
| throw (Error) throwable; |
| } |
| } |
| |
| @Override |
| void putThread(Waiter waiter, Thread newValue) { |
| UNSAFE.putObject(waiter, WAITER_THREAD_OFFSET, newValue); |
| } |
| |
| @Override |
| void putNext(Waiter waiter, Waiter newValue) { |
| UNSAFE.putObject(waiter, WAITER_NEXT_OFFSET, newValue); |
| } |
| |
| /** |
| * Performs a CAS operation on the {@link #waiters} field. |
| */ |
| @Override |
| boolean casWaiters(AbstractFuture<?> future, Waiter expect, Waiter |
| update) { |
| return UNSAFE |
| .compareAndSwapObject(future, WAITERS_OFFSET, expect, update); |
| } |
| |
| /** |
| * Performs a CAS operation on the {@link #listeners} field. |
| */ |
| @Override |
| boolean casListeners( |
| AbstractFuture<?> future, Listener expect, Listener update) { |
| return UNSAFE |
| .compareAndSwapObject(future, LISTENERS_OFFSET, expect, update); |
| } |
| |
| /** |
| * Performs a CAS operation on the {@link #value} field. |
| */ |
| @Override |
| boolean casValue(AbstractFuture<?> future, Object expect, Object update) { |
| return UNSAFE.compareAndSwapObject(future, VALUE_OFFSET, expect, update); |
| } |
| } |
| |
| /** |
| * {@link AtomicHelper} based on {@link AtomicReferenceFieldUpdater}. |
| */ |
| @SuppressWarnings("visibilitymodifier") |
| private static final class SafeAtomicHelper extends AtomicHelper { |
| final AtomicReferenceFieldUpdater<Waiter, Thread> waiterThreadUpdater; |
| final AtomicReferenceFieldUpdater<Waiter, Waiter> waiterNextUpdater; |
| final AtomicReferenceFieldUpdater<AbstractFuture, Waiter> waitersUpdater; |
| final AtomicReferenceFieldUpdater<AbstractFuture, Listener> |
| listenersUpdater; |
| final AtomicReferenceFieldUpdater<AbstractFuture, Object> valueUpdater; |
| |
| SafeAtomicHelper( |
| AtomicReferenceFieldUpdater<Waiter, Thread> waiterThreadUpdater, |
| AtomicReferenceFieldUpdater<Waiter, Waiter> waiterNextUpdater, |
| AtomicReferenceFieldUpdater<AbstractFuture, Waiter> waitersUpdater, |
| AtomicReferenceFieldUpdater<AbstractFuture, Listener> listenersUpdater, |
| AtomicReferenceFieldUpdater<AbstractFuture, Object> valueUpdater) { |
| this.waiterThreadUpdater = waiterThreadUpdater; |
| this.waiterNextUpdater = waiterNextUpdater; |
| this.waitersUpdater = waitersUpdater; |
| this.listenersUpdater = listenersUpdater; |
| this.valueUpdater = valueUpdater; |
| } |
| |
| @Override |
| void putThread(Waiter waiter, Thread newValue) { |
| waiterThreadUpdater.lazySet(waiter, newValue); |
| } |
| |
| @Override |
| void putNext(Waiter waiter, Waiter newValue) { |
| waiterNextUpdater.lazySet(waiter, newValue); |
| } |
| |
| @Override |
| boolean casWaiters(AbstractFuture<?> future, Waiter expect, Waiter |
| update) { |
| return waitersUpdater.compareAndSet(future, expect, update); |
| } |
| |
| @Override |
| boolean casListeners( |
| AbstractFuture<?> future, Listener expect, Listener update) { |
| return listenersUpdater.compareAndSet(future, expect, update); |
| } |
| |
| @Override |
| boolean casValue(AbstractFuture<?> future, Object expect, Object update) { |
| return valueUpdater.compareAndSet(future, expect, update); |
| } |
| } |
| |
| /** |
| * {@link AtomicHelper} based on {@code synchronized} and volatile writes. |
| * <p> |
| * <p>This is an implementation of last resort for when certain basic VM |
| * features are broken (like AtomicReferenceFieldUpdater). |
| */ |
| private static final class SynchronizedHelper extends AtomicHelper { |
| @Override |
| void putThread(Waiter waiter, Thread newValue) { |
| waiter.thread = newValue; |
| } |
| |
| @Override |
| void putNext(Waiter waiter, Waiter newValue) { |
| waiter.next = newValue; |
| } |
| |
| @Override |
| boolean casWaiters(AbstractFuture<?> future, Waiter expect, Waiter |
| update) { |
| synchronized (future) { |
| if (future.waiters == expect) { |
| future.waiters = update; |
| return true; |
| } |
| return false; |
| } |
| } |
| |
| @Override |
| boolean casListeners( |
| AbstractFuture<?> future, Listener expect, Listener update) { |
| synchronized (future) { |
| if (future.listeners == expect) { |
| future.listeners = update; |
| return true; |
| } |
| return false; |
| } |
| } |
| |
| @Override |
| boolean casValue(AbstractFuture<?> future, Object expect, Object update) { |
| synchronized (future) { |
| if (future.value == expect) { |
| future.value = update; |
| return true; |
| } |
| return false; |
| } |
| } |
| } |
| |
| private static CancellationException cancellationExceptionWithCause( |
| @Nullable String message, @Nullable Throwable cause) { |
| CancellationException exception = new CancellationException(message); |
| exception.initCause(cause); |
| return exception; |
| } |
| |
| /** |
| * Returns an {@link Executor} that runs each task in the thread that invokes |
| * {@link Executor#execute execute}, as in {@link CallerRunsPolicy}. |
| * <p> |
| * <p>This instance is equivalent to: <pre> {@code |
| * final class DirectExecutor implements Executor { |
| * public void execute(Runnable r) { |
| * r.run(); |
| * } |
| * }}</pre> |
| */ |
| public static Executor directExecutor() { |
| return DirectExecutor.INSTANCE; |
| } |
| |
| /** |
| * See {@link #directExecutor} for behavioral notes. |
| */ |
| private enum DirectExecutor implements Executor { |
| INSTANCE; |
| |
| @Override |
| public void execute(Runnable command) { |
| command.run(); |
| } |
| |
| @Override |
| public String toString() { |
| return "MoreExecutors.directExecutor()"; |
| } |
| } |
| |
| } |