io.netty.handler.flush.FlushConsolidationHandler Maven / Gradle / Ivy
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/*
* Copyright 2016 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:
*
* https://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.handler.flush;
import io.netty.channel.Channel;
import io.netty.channel.ChannelDuplexHandler;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelOutboundHandler;
import io.netty.channel.ChannelOutboundInvoker;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.ChannelPromise;
import io.netty.util.internal.ObjectUtil;
import java.util.concurrent.Future;
/**
* {@link ChannelDuplexHandler} which consolidates {@link Channel#flush()} / {@link ChannelHandlerContext#flush()}
* operations (which also includes
* {@link Channel#writeAndFlush(Object)} / {@link Channel#writeAndFlush(Object, ChannelPromise)} and
* {@link ChannelOutboundInvoker#writeAndFlush(Object)} /
* {@link ChannelOutboundInvoker#writeAndFlush(Object, ChannelPromise)}).
*
* Flush operations are generally speaking expensive as these may trigger a syscall on the transport level. Thus it is
* in most cases (where write latency can be traded with throughput) a good idea to try to minimize flush operations
* as much as possible.
*
* If a read loop is currently ongoing, {@link #flush(ChannelHandlerContext)} will not be passed on to the next
* {@link ChannelOutboundHandler} in the {@link ChannelPipeline}, as it will pick up any pending flushes when
* {@link #channelReadComplete(ChannelHandlerContext)} is triggered.
* If no read loop is ongoing, the behavior depends on the {@code consolidateWhenNoReadInProgress} constructor argument:
*
* - if {@code false}, flushes are passed on to the next handler directly;
* - if {@code true}, the invocation of the next handler is submitted as a separate task on the event loop. Under
* high throughput, this gives the opportunity to process other flushes before the task gets executed, thus
* batching multiple flushes into one.
*
* If {@code explicitFlushAfterFlushes} is reached the flush will be forwarded as well (whether while in a read loop, or
* while batching outside of a read loop).
*
* If the {@link Channel} becomes non-writable it will also try to execute any pending flush operations.
*
* The {@link FlushConsolidationHandler} should be put as first {@link ChannelHandler} in the
* {@link ChannelPipeline} to have the best effect.
*/
public class FlushConsolidationHandler extends ChannelDuplexHandler {
private final int explicitFlushAfterFlushes;
private final boolean consolidateWhenNoReadInProgress;
private final Runnable flushTask;
private int flushPendingCount;
private boolean readInProgress;
private ChannelHandlerContext ctx;
private Future nextScheduledFlush;
/**
* The default number of flushes after which a flush will be forwarded to downstream handlers (whether while in a
* read loop, or while batching outside of a read loop).
*/
public static final int DEFAULT_EXPLICIT_FLUSH_AFTER_FLUSHES = 256;
/**
* Create new instance which explicit flush after {@value DEFAULT_EXPLICIT_FLUSH_AFTER_FLUSHES} pending flush
* operations at the latest.
*/
public FlushConsolidationHandler() {
this(DEFAULT_EXPLICIT_FLUSH_AFTER_FLUSHES, false);
}
/**
* Create new instance which doesn't consolidate flushes when no read is in progress.
*
* @param explicitFlushAfterFlushes the number of flushes after which an explicit flush will be done.
*/
public FlushConsolidationHandler(int explicitFlushAfterFlushes) {
this(explicitFlushAfterFlushes, false);
}
/**
* Create new instance.
*
* @param explicitFlushAfterFlushes the number of flushes after which an explicit flush will be done.
* @param consolidateWhenNoReadInProgress whether to consolidate flushes even when no read loop is currently
* ongoing.
*/
public FlushConsolidationHandler(int explicitFlushAfterFlushes, boolean consolidateWhenNoReadInProgress) {
this.explicitFlushAfterFlushes =
ObjectUtil.checkPositive(explicitFlushAfterFlushes, "explicitFlushAfterFlushes");
this.consolidateWhenNoReadInProgress = consolidateWhenNoReadInProgress;
this.flushTask = consolidateWhenNoReadInProgress ?
new Runnable() {
@Override
public void run() {
if (flushPendingCount > 0 && !readInProgress) {
flushPendingCount = 0;
nextScheduledFlush = null;
ctx.flush();
} // else we'll flush when the read completes
}
}
: null;
}
@Override
public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
this.ctx = ctx;
}
@Override
public void flush(ChannelHandlerContext ctx) throws Exception {
if (readInProgress) {
// If there is still a read in progress we are sure we will see a channelReadComplete(...) call. Thus
// we only need to flush if we reach the explicitFlushAfterFlushes limit.
if (++flushPendingCount == explicitFlushAfterFlushes) {
flushNow(ctx);
}
} else if (consolidateWhenNoReadInProgress) {
// Flush immediately if we reach the threshold, otherwise schedule
if (++flushPendingCount == explicitFlushAfterFlushes) {
flushNow(ctx);
} else {
scheduleFlush(ctx);
}
} else {
// Always flush directly
flushNow(ctx);
}
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
// This may be the last event in the read loop, so flush now!
resetReadAndFlushIfNeeded(ctx);
ctx.fireChannelReadComplete();
}
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
readInProgress = true;
ctx.fireChannelRead(msg);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
// To ensure we not miss to flush anything, do it now.
resetReadAndFlushIfNeeded(ctx);
ctx.fireExceptionCaught(cause);
}
@Override
public void disconnect(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception {
// Try to flush one last time if flushes are pending before disconnect the channel.
resetReadAndFlushIfNeeded(ctx);
ctx.disconnect(promise);
}
@Override
public void close(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception {
// Try to flush one last time if flushes are pending before close the channel.
resetReadAndFlushIfNeeded(ctx);
ctx.close(promise);
}
@Override
public void channelWritabilityChanged(ChannelHandlerContext ctx) throws Exception {
if (!ctx.channel().isWritable()) {
// The writability of the channel changed to false, so flush all consolidated flushes now to free up memory.
flushIfNeeded(ctx);
}
ctx.fireChannelWritabilityChanged();
}
@Override
public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
flushIfNeeded(ctx);
}
private void resetReadAndFlushIfNeeded(ChannelHandlerContext ctx) {
readInProgress = false;
flushIfNeeded(ctx);
}
private void flushIfNeeded(ChannelHandlerContext ctx) {
if (flushPendingCount > 0) {
flushNow(ctx);
}
}
private void flushNow(ChannelHandlerContext ctx) {
cancelScheduledFlush();
flushPendingCount = 0;
ctx.flush();
}
private void scheduleFlush(final ChannelHandlerContext ctx) {
if (nextScheduledFlush == null) {
// Run as soon as possible, but still yield to give a chance for additional writes to enqueue.
nextScheduledFlush = ctx.channel().eventLoop().submit(flushTask);
}
}
private void cancelScheduledFlush() {
if (nextScheduledFlush != null) {
nextScheduledFlush.cancel(false);
nextScheduledFlush = null;
}
}
}