1 /* 2 * Copyright 2016 The gRPC Authors 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 io.grpc.internal; 18 19 import static com.google.common.base.Preconditions.checkNotNull; 20 21 import com.google.common.annotations.VisibleForTesting; 22 import java.util.ArrayDeque; 23 import java.util.Queue; 24 import java.util.logging.Level; 25 import java.util.logging.Logger; 26 import javax.annotation.concurrent.GuardedBy; 27 import javax.annotation.concurrent.ThreadSafe; 28 29 /** 30 * The thread-less Channel Executor used to run the state mutation logic in {@link 31 * ManagedChannelImpl}, {@link InternalSubchannel} and {@link io.grpc.LoadBalancer}s. 32 * 33 * <p>Tasks are queued until {@link #drain} is called. Tasks are guaranteed to be run in the same 34 * order as they are submitted. 35 */ 36 @ThreadSafe 37 class ChannelExecutor { 38 private static final Logger log = Logger.getLogger(ChannelExecutor.class.getName()); 39 40 private final Object lock = new Object(); 41 42 @GuardedBy("lock") 43 private final Queue<Runnable> queue = new ArrayDeque<Runnable>(); 44 @GuardedBy("lock") 45 private boolean draining; 46 47 /** 48 * Run all tasks in the queue in the current thread, if no other thread is in this method. 49 * Otherwise do nothing. 50 * 51 * <p>Upon returning, it guarantees that all tasks submitted by {@code executeLater()} before it 52 * have been or will eventually be run, while not requiring any more calls to {@code drain()}. 53 */ drain()54 final void drain() { 55 boolean drainLeaseAcquired = false; 56 while (true) { 57 Runnable runnable; 58 synchronized (lock) { 59 if (!drainLeaseAcquired) { 60 if (draining) { 61 return; 62 } 63 draining = true; 64 drainLeaseAcquired = true; 65 } 66 runnable = queue.poll(); 67 if (runnable == null) { 68 draining = false; 69 break; 70 } 71 } 72 try { 73 runnable.run(); 74 } catch (Throwable t) { 75 handleUncaughtThrowable(t); 76 } 77 } 78 } 79 80 /** 81 * Enqueues a task that will be run when {@link #drain} is called. 82 * 83 * @return this ChannelExecutor 84 */ executeLater(Runnable runnable)85 final ChannelExecutor executeLater(Runnable runnable) { 86 synchronized (lock) { 87 queue.add(checkNotNull(runnable, "runnable is null")); 88 } 89 return this; 90 } 91 92 @VisibleForTesting numPendingTasks()93 final int numPendingTasks() { 94 synchronized (lock) { 95 return queue.size(); 96 } 97 } 98 99 /** 100 * Handle a throwable from a task. 101 * 102 * <p>The default implementation logs a warning. 103 */ handleUncaughtThrowable(Throwable t)104 void handleUncaughtThrowable(Throwable t) { 105 log.log(Level.WARNING, "Runnable threw exception in ChannelExecutor", t); 106 } 107 } 108