/*
* 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:
*
* 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 com.linecorp.armeria.internal;
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;
/**
* {@link ChannelDuplexHandler} which consolidate {@link ChannelOutboundInvoker#flush()} operations (which also
* includes {@link ChannelOutboundInvoker#writeAndFlush(Object)} and
* {@link ChannelOutboundInvoker#writeAndFlush(Object, ChannelPromise)}).
*
* <p>Flush operations are general 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.
*
* <p>When {@link #flush(ChannelHandlerContext)} is called it will only pass it on to the next
* {@link ChannelOutboundHandler} in the {@link ChannelPipeline} if no read loop is currently ongoing
* as it will pick up any pending flushes when {@link #channelReadComplete(ChannelHandlerContext)} is trigged.
* If {@code explicitFlushAfterFlushes} is reached the flush will also be forwarded as well.
*
* <p>If the {@link Channel} becomes non-writable it will also try to execute any pending flush operations.
*
* <p>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 int flushPendingCount;
private boolean readInprogess;
/**
* Create new instance which explicit flush after 256 pending flush operations latest.
*/
public FlushConsolidationHandler() {
this(256);
}
/**
* Create new instance.
*
* @param explicitFlushAfterFlushes the number of flushes after which an explicit flush will be done.
*/
public FlushConsolidationHandler(int explicitFlushAfterFlushes) {
this.explicitFlushAfterFlushes = ObjectUtil.checkPositive(explicitFlushAfterFlushes,
"explicitFlushAfterFlushes");
}
@Override
public void flush(ChannelHandlerContext ctx) throws Exception {
if (readInprogess) {
// 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) {
flushPendingCount = 0;
ctx.flush();
}
return;
}
ctx.flush();
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
// This may be the last event in the read loop, so flush now!
flushIfNeeded(ctx, true);
ctx.fireChannelReadComplete();
}
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
readInprogess = 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.
flushIfNeeded(ctx, true);
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.
flushIfNeeded(ctx, true);
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.
flushIfNeeded(ctx, true);
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, false);
}
ctx.fireChannelWritabilityChanged();
}
@Override
public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
flushIfNeeded(ctx, false);
}
private void flushIfNeeded(ChannelHandlerContext ctx, boolean resetReadInProgress) {
if (resetReadInProgress) {
readInprogess = false;
}
if (flushPendingCount > 0) {
flushPendingCount = 0;
ctx.flush();
}
}
}