io.grpc.internal.ChannelExecutor Maven / Gradle / Ivy
/*
* Copyright 2016, gRPC Authors All rights reserved.
*
* 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 io.grpc.internal;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.VisibleForTesting;
import java.util.LinkedList;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.annotation.concurrent.GuardedBy;
import javax.annotation.concurrent.ThreadSafe;
/**
* The thread-less Channel Executor used to run the state mutation logic in {@link
* ManagedChannelImpl}, {@link InternalSubchannel} and {@link io.grpc.LoadBalancer}s.
*
* Tasks are queued until {@link #drain} is called. Tasks are guaranteed to be run in the same
* order as they are submitted.
*/
@ThreadSafe
final class ChannelExecutor {
private static final Logger log = Logger.getLogger(ChannelExecutor.class.getName());
private final Object lock = new Object();
@GuardedBy("lock")
private final LinkedList queue = new LinkedList();
@GuardedBy("lock")
private boolean draining;
/**
* Run all tasks in the queue in the current thread, if no other thread is in this method.
* Otherwise do nothing.
*
* Upon returning, it guarantees that all tasks submitted by {@code executeLater()} before it
* have been or will eventually be run, while not requiring any more calls to {@code drain()}.
*/
void drain() {
boolean drainLeaseAcquired = false;
while (true) {
Runnable runnable;
synchronized (lock) {
if (!drainLeaseAcquired) {
if (draining) {
return;
}
draining = true;
drainLeaseAcquired = true;
}
runnable = queue.poll();
if (runnable == null) {
draining = false;
break;
}
}
try {
runnable.run();
} catch (Throwable t) {
log.log(Level.WARNING, "Runnable threw exception in ChannelExecutor", t);
}
}
}
/**
* Enqueues a task that will be run when {@link #drain} is called.
*
* @return this ChannelExecutor
*/
ChannelExecutor executeLater(Runnable runnable) {
synchronized (lock) {
queue.add(checkNotNull(runnable, "runnable is null"));
}
return this;
}
@VisibleForTesting
int numPendingTasks() {
synchronized (lock) {
return queue.size();
}
}
}