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/*
* Copyright 2014 The Netty Project
*
* The Netty Project licenses this file to you 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.netty.channel;
import io.netty.util.Recycler;
import io.netty.util.ReferenceCountUtil;
import io.netty.util.concurrent.PromiseCombiner;
import io.netty.util.internal.ObjectUtil;
import io.netty.util.internal.SystemPropertyUtil;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;
/**
* A queue of write operations which are pending for later execution. It also updates the
* {@linkplain Channel#isWritable() writability} of the associated {@link Channel}, so that
* the pending write operations are also considered to determine the writability.
*/
public final class PendingWriteQueue {
private static final InternalLogger logger = InternalLoggerFactory.getInstance(PendingWriteQueue.class);
// Assuming a 64-bit JVM:
// - 16 bytes object header
// - 4 reference fields
// - 1 long fields
private static final int PENDING_WRITE_OVERHEAD =
SystemPropertyUtil.getInt("io.netty.transport.pendingWriteSizeOverhead", 64);
private final ChannelHandlerContext ctx;
private final PendingBytesTracker tracker;
// head and tail pointers for the linked-list structure. If empty head and tail are null.
private PendingWrite head;
private PendingWrite tail;
private int size;
private long bytes;
public PendingWriteQueue(ChannelHandlerContext ctx) {
tracker = PendingBytesTracker.newTracker(ctx.channel());
this.ctx = ctx;
}
/**
* Returns {@code true} if there are no pending write operations left in this queue.
*/
public boolean isEmpty() {
assert ctx.executor().inEventLoop();
return head == null;
}
/**
* Returns the number of pending write operations.
*/
public int size() {
assert ctx.executor().inEventLoop();
return size;
}
/**
* Returns the total number of bytes that are pending because of pending messages. This is only an estimate so
* it should only be treated as a hint.
*/
public long bytes() {
assert ctx.executor().inEventLoop();
return bytes;
}
private int size(Object msg) {
// It is possible for writes to be triggered from removeAndFailAll(). To preserve ordering,
// we should add them to the queue and let removeAndFailAll() fail them later.
int messageSize = tracker.size(msg);
if (messageSize < 0) {
// Size may be unknown so just use 0
messageSize = 0;
}
return messageSize + PENDING_WRITE_OVERHEAD;
}
/**
* Add the given {@code msg} and {@link ChannelPromise}.
*/
public void add(Object msg, ChannelPromise promise) {
assert ctx.executor().inEventLoop();
if (msg == null) {
throw new NullPointerException("msg");
}
if (promise == null) {
throw new NullPointerException("promise");
}
// It is possible for writes to be triggered from removeAndFailAll(). To preserve ordering,
// we should add them to the queue and let removeAndFailAll() fail them later.
int messageSize = size(msg);
PendingWrite write = PendingWrite.newInstance(msg, messageSize, promise);
PendingWrite currentTail = tail;
if (currentTail == null) {
tail = head = write;
} else {
currentTail.next = write;
tail = write;
}
size ++;
bytes += messageSize;
tracker.incrementPendingOutboundBytes(write.size);
}
/**
* Remove all pending write operation and performs them via
* {@link ChannelHandlerContext#write(Object, ChannelPromise)}.
*
* @return {@link ChannelFuture} if something was written and {@code null}
* if the {@link PendingWriteQueue} is empty.
*/
public ChannelFuture removeAndWriteAll() {
assert ctx.executor().inEventLoop();
if (isEmpty()) {
return null;
}
ChannelPromise p = ctx.newPromise();
PromiseCombiner combiner = new PromiseCombiner();
try {
// It is possible for some of the written promises to trigger more writes. The new writes
// will "revive" the queue, so we need to write them up until the queue is empty.
for (PendingWrite write = head; write != null; write = head) {
head = tail = null;
size = 0;
bytes = 0;
while (write != null) {
PendingWrite next = write.next;
Object msg = write.msg;
ChannelPromise promise = write.promise;
recycle(write, false);
combiner.add(promise);
ctx.write(msg, promise);
write = next;
}
}
combiner.finish(p);
} catch (Throwable cause) {
p.setFailure(cause);
}
assertEmpty();
return p;
}
/**
* Remove all pending write operation and fail them with the given {@link Throwable}. The message will be released
* via {@link ReferenceCountUtil#safeRelease(Object)}.
*/
public void removeAndFailAll(Throwable cause) {
assert ctx.executor().inEventLoop();
if (cause == null) {
throw new NullPointerException("cause");
}
// It is possible for some of the failed promises to trigger more writes. The new writes
// will "revive" the queue, so we need to clean them up until the queue is empty.
for (PendingWrite write = head; write != null; write = head) {
head = tail = null;
size = 0;
bytes = 0;
while (write != null) {
PendingWrite next = write.next;
ReferenceCountUtil.safeRelease(write.msg);
ChannelPromise promise = write.promise;
recycle(write, false);
safeFail(promise, cause);
write = next;
}
}
assertEmpty();
}
/**
* Remove a pending write operation and fail it with the given {@link Throwable}. The message will be released via
* {@link ReferenceCountUtil#safeRelease(Object)}.
*/
public void removeAndFail(Throwable cause) {
assert ctx.executor().inEventLoop();
if (cause == null) {
throw new NullPointerException("cause");
}
PendingWrite write = head;
if (write == null) {
return;
}
ReferenceCountUtil.safeRelease(write.msg);
ChannelPromise promise = write.promise;
safeFail(promise, cause);
recycle(write, true);
}
private void assertEmpty() {
assert tail == null && head == null && size == 0;
}
/**
* Removes a pending write operation and performs it via
* {@link ChannelHandlerContext#write(Object, ChannelPromise)}.
*
* @return {@link ChannelFuture} if something was written and {@code null}
* if the {@link PendingWriteQueue} is empty.
*/
public ChannelFuture removeAndWrite() {
assert ctx.executor().inEventLoop();
PendingWrite write = head;
if (write == null) {
return null;
}
Object msg = write.msg;
ChannelPromise promise = write.promise;
recycle(write, true);
return ctx.write(msg, promise);
}
/**
* Removes a pending write operation and release it's message via {@link ReferenceCountUtil#safeRelease(Object)}.
*
* @return {@link ChannelPromise} of the pending write or {@code null} if the queue is empty.
*
*/
public ChannelPromise remove() {
assert ctx.executor().inEventLoop();
PendingWrite write = head;
if (write == null) {
return null;
}
ChannelPromise promise = write.promise;
ReferenceCountUtil.safeRelease(write.msg);
recycle(write, true);
return promise;
}
/**
* Return the current message or {@code null} if empty.
*/
public Object current() {
assert ctx.executor().inEventLoop();
PendingWrite write = head;
if (write == null) {
return null;
}
return write.msg;
}
private void recycle(PendingWrite write, boolean update) {
final PendingWrite next = write.next;
final long writeSize = write.size;
if (update) {
if (next == null) {
// Handled last PendingWrite so rest head and tail
// Guard against re-entrance by directly reset
head = tail = null;
size = 0;
bytes = 0;
} else {
head = next;
size --;
bytes -= writeSize;
assert size > 0 && bytes >= 0;
}
}
write.recycle();
tracker.decrementPendingOutboundBytes(writeSize);
}
private static void safeFail(ChannelPromise promise, Throwable cause) {
if (!(promise instanceof VoidChannelPromise) && !promise.tryFailure(cause)) {
logger.warn("Failed to mark a promise as failure because it's done already: {}", promise, cause);
}
}
/**
* Holds all meta-data and construct the linked-list structure.
*/
static final class PendingWrite {
private static final Recycler RECYCLER = new Recycler() {
@Override
protected PendingWrite newObject(Handle handle) {
return new PendingWrite(handle);
}
};
private final Recycler.Handle handle;
private PendingWrite next;
private long size;
private ChannelPromise promise;
private Object msg;
private PendingWrite(Recycler.Handle handle) {
this.handle = handle;
}
static PendingWrite newInstance(Object msg, int size, ChannelPromise promise) {
PendingWrite write = RECYCLER.get();
write.size = size;
write.msg = msg;
write.promise = promise;
return write;
}
private void recycle() {
size = 0;
next = null;
msg = null;
promise = null;
handle.recycle(this);
}
}
}
