Java tutorial
/* * 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)}). * * 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. * * 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. * * 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 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(); } } }