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/*
* Copyright 2015, Google Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
*
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package io.grpc.netty;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelPromise;
import java.util.ArrayDeque;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.atomic.AtomicBoolean;
/**
* A queue of pending writes to a {@link Channel} that is flushed as a single unit.
*/
class WriteQueue {
// Dequeue in chunks, so we don't have to acquire the queue's log too often.
@VisibleForTesting
static final int DEQUE_CHUNK_SIZE = 128;
/**
* {@link Runnable} used to schedule work onto the tail of the event loop.
*/
private final Runnable later = new Runnable() {
@Override
public void run() {
flush();
}
};
private final Channel channel;
private final BlockingQueue queue;
private final AtomicBoolean scheduled = new AtomicBoolean();
/**
* ArrayDeque to copy queue into when flushing in event loop.
*/
private final ArrayDeque writeChunk =
new ArrayDeque(DEQUE_CHUNK_SIZE);
public WriteQueue(Channel channel) {
this.channel = Preconditions.checkNotNull(channel, "channel");
queue = new LinkedBlockingQueue();
}
/**
* Schedule a flush on the channel.
*/
void scheduleFlush() {
if (scheduled.compareAndSet(false, true)) {
// Add the queue to the tail of the event loop so writes will be executed immediately
// inside the event loop. Note DO NOT do channel.write outside the event loop as
// it will not wake up immediately without a flush.
channel.eventLoop().execute(later);
}
}
/**
* Enqueue a write command on the channel.
*
* @param command a write to be executed on the channel.
* @param flush true if a flush of the write should be schedule, false if a later call to
* enqueue will schedule the flush.
*/
ChannelFuture enqueue(QueuedCommand command, boolean flush) {
return enqueue(command, channel.newPromise(), flush);
}
/**
* Enqueue a write command with a completion listener.
*
* @param command a write to be executed on the channel.
* @param promise to be marked on the completion of the write.
* @param flush true if a flush of the write should be schedule, false if a later call to
* enqueue will schedule the flush.
*/
ChannelFuture enqueue(QueuedCommand command, ChannelPromise promise, boolean flush) {
// Detect erroneous code that tries to reuse command objects.
Preconditions.checkArgument(command.promise() == null, "promise must not be set on command");
command.promise(promise);
queue.add(command);
if (flush) {
scheduleFlush();
}
return promise;
}
/**
* Process the queue of commands and dispatch them to the stream. This method is only
* called in the event loop
*/
private void flush() {
try {
boolean flushed = false;
while (queue.drainTo(writeChunk, DEQUE_CHUNK_SIZE) > 0) {
while (writeChunk.size() > 0) {
QueuedCommand cmd = writeChunk.poll();
channel.write(cmd, cmd.promise());
}
// Flush each chunk so we are releasing buffers periodically. In theory this loop
// might never end as new events are continuously added to the queue, if we never
// flushed in that case we would be guaranteed to OOM.
flushed = true;
channel.flush();
}
if (!flushed) {
// Must flush at least once
channel.flush();
}
} finally {
// Mark the write as done, if the queue is non-empty after marking trigger a new write.
scheduled.set(false);
if (!queue.isEmpty()) {
scheduleFlush();
}
}
}
abstract static class AbstractQueuedCommand implements QueuedCommand {
private ChannelPromise promise;
@Override
public final void promise(ChannelPromise promise) {
this.promise = promise;
}
@Override
public final ChannelPromise promise() {
return promise;
}
}
/**
* Simple wrapper type around a command and its optional completion listener.
*/
interface QueuedCommand {
/**
* Returns the promise beeing notified of the success/failure of the write.
*/
ChannelPromise promise();
/**
* Sets the promise.
*/
void promise(ChannelPromise promise);
}
}
