com.google.common.util.concurrent.AggregateFutureState Maven / Gradle / Ivy
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This artifact provides a single jar that contains all classes required to use remote EJB and JMS, including
all dependencies. It is intended for use by those not using maven, maven users should just import the EJB and
JMS BOM's instead (shaded JAR's cause lots of problems with maven, as it is very easy to inadvertently end up
with different versions on classes on the class path).
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/*
* Copyright (C) 2015 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.
*/
package com.google.common.util.concurrent;
import static com.google.common.collect.Sets.newConcurrentHashSet;
import static java.util.Objects.requireNonNull;
import static java.util.concurrent.atomic.AtomicIntegerFieldUpdater.newUpdater;
import static java.util.concurrent.atomic.AtomicReferenceFieldUpdater.newUpdater;
import com.google.common.annotations.GwtCompatible;
import com.google.j2objc.annotations.ReflectionSupport;
import java.util.Set;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import java.util.logging.Level;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* A helper which does some thread-safe operations for aggregate futures, which must be implemented
* differently in GWT. Namely:
*
*
* - Lazily initializes a set of seen exceptions
*
- Decrements a counter atomically
*
*/
@GwtCompatible(emulated = true)
@ReflectionSupport(value = ReflectionSupport.Level.FULL)
@ElementTypesAreNonnullByDefault
abstract class AggregateFutureState
extends AbstractFuture.TrustedFuture {
// Lazily initialized the first time we see an exception; not released until all the input futures
// have completed and we have processed them all.
@CheckForNull private volatile Set seenExceptions = null;
private volatile int remaining;
private static final AtomicHelper ATOMIC_HELPER;
private static final LazyLogger log = new LazyLogger(AggregateFutureState.class);
static {
AtomicHelper helper;
Throwable thrownReflectionFailure = null;
try {
helper =
new SafeAtomicHelper(
newUpdater(AggregateFutureState.class, Set.class, "seenExceptions"),
newUpdater(AggregateFutureState.class, "remaining"));
} catch (Throwable reflectionFailure) { // sneaky checked exception
// 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.
thrownReflectionFailure = reflectionFailure;
helper = new SynchronizedAtomicHelper();
}
ATOMIC_HELPER = helper;
// Log after all static init is finished; if an installed logger uses any Futures methods, it
// shouldn't break in cases where reflection is missing/broken.
if (thrownReflectionFailure != null) {
log.get().log(Level.SEVERE, "SafeAtomicHelper is broken!", thrownReflectionFailure);
}
}
AggregateFutureState(int remainingFutures) {
this.remaining = remainingFutures;
}
final Set getOrInitSeenExceptions() {
/*
* The initialization of seenExceptions has to be more complicated than we'd like. The simple
* approach would be for each caller CAS it from null to a Set populated with its exception. But
* there's another race: If the first thread fails with an exception and a second thread
* immediately fails with the same exception:
*
* Thread1: calls setException(), which returns true, context switch before it can CAS
* seenExceptions to its exception
*
* Thread2: calls setException(), which returns false, CASes seenExceptions to its exception,
* and wrongly believes that its exception is new (leading it to logging it when it shouldn't)
*
* Our solution is for threads to CAS seenExceptions from null to a Set populated with _the
* initial exception_, no matter which thread does the work. This ensures that seenExceptions
* always contains not just the current thread's exception but also the initial thread's.
*/
Set seenExceptionsLocal = seenExceptions;
if (seenExceptionsLocal == null) {
// TODO(cpovirk): Should we use a simpler (presumably cheaper) data structure?
/*
* Using weak references here could let us release exceptions earlier, but:
*
* 1. On Android, querying a WeakReference blocks if the GC is doing an otherwise-concurrent
* pass.
*
* 2. We would probably choose to compare exceptions using == instead of equals() (for
* consistency with how weak references are cleared). That's a behavior change -- arguably the
* removal of a feature.
*
* Fortunately, exceptions rarely contain references to expensive resources.
*/
//
seenExceptionsLocal = newConcurrentHashSet();
/*
* Other handleException() callers may see this as soon as we publish it. We need to populate
* it with the initial failure before we do, or else they may think that the initial failure
* has never been seen before.
*/
addInitialException(seenExceptionsLocal);
ATOMIC_HELPER.compareAndSetSeenExceptions(this, null, seenExceptionsLocal);
/*
* If another handleException() caller created the set, we need to use that copy in case yet
* other callers have added to it.
*
* This read is guaranteed to get us the right value because we only set this once (here).
*
* requireNonNull is safe because either our compareAndSet succeeded or it failed because
* another thread did it for us.
*/
seenExceptionsLocal = requireNonNull(seenExceptions);
}
return seenExceptionsLocal;
}
/** Populates {@code seen} with the exception that was passed to {@code setException}. */
abstract void addInitialException(Set seen);
final int decrementRemainingAndGet() {
return ATOMIC_HELPER.decrementAndGetRemainingCount(this);
}
final void clearSeenExceptions() {
seenExceptions = null;
}
private abstract static class AtomicHelper {
/** Atomic compare-and-set of the {@link AggregateFutureState#seenExceptions} field. */
abstract void compareAndSetSeenExceptions(
AggregateFutureState state, @CheckForNull Set expect, Set update);
/** Atomic decrement-and-get of the {@link AggregateFutureState#remaining} field. */
abstract int decrementAndGetRemainingCount(AggregateFutureState state);
}
private static final class SafeAtomicHelper extends AtomicHelper {
final AtomicReferenceFieldUpdater, @Nullable Set>
seenExceptionsUpdater;
final AtomicIntegerFieldUpdater> remainingCountUpdater;
@SuppressWarnings({"rawtypes", "unchecked"}) // Unavoidable with reflection API
SafeAtomicHelper(
AtomicReferenceFieldUpdater seenExceptionsUpdater,
AtomicIntegerFieldUpdater remainingCountUpdater) {
this.seenExceptionsUpdater =
(AtomicReferenceFieldUpdater, @Nullable Set>)
seenExceptionsUpdater;
this.remainingCountUpdater =
(AtomicIntegerFieldUpdater>) remainingCountUpdater;
}
@Override
void compareAndSetSeenExceptions(
AggregateFutureState state, @CheckForNull Set expect, Set update) {
seenExceptionsUpdater.compareAndSet(state, expect, update);
}
@Override
int decrementAndGetRemainingCount(AggregateFutureState state) {
return remainingCountUpdater.decrementAndGet(state);
}
}
private static final class SynchronizedAtomicHelper extends AtomicHelper {
@Override
void compareAndSetSeenExceptions(
AggregateFutureState state, @CheckForNull Set expect, Set update) {
synchronized (state) {
if (state.seenExceptions == expect) {
state.seenExceptions = update;
}
}
}
@Override
int decrementAndGetRemainingCount(AggregateFutureState state) {
synchronized (state) {
return --state.remaining;
}
}
}
}