netty server的read流程是怎样的
本篇内容主要讲解“netty server的read流程是怎样的”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“netty server的read流程是怎样的”吧!
客户端发送数据过来的时候，netty具体是怎么执行读取任务的。
仍然是从NioEventLoop开始，还是NioEventLoop.processSelectedKey这个方法，
private static void processSelectedKey(SelectionKey k, AbstractNioChannel ch) {
final NioUnsafe unsafe = ch.unsafe();
if (!k.isValid()) {
// close the channel if the key is not valid anymore
unsafe.close(unsafe.voidPromise());
return;
}
try {
int readyOps = k.readyOps();
// Also check for readOps of 0 to workaround possible JDK bug which may otherwise lead
// to a spin loop
if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
unsafe.read();
if (!ch.isOpen()) {
// Connection already closed - no need to handle write.
return;
}
}
if ((readyOps & SelectionKey.OP_WRITE) != 0) {
// Call forceFlush which will also take care of clear the OP_WRITE once there is nothing left to write
ch.unsafe().forceFlush();
}
if ((readyOps & SelectionKey.OP_CONNECT) != 0) {
// remove OP_CONNECT as otherwise Selector.select(..) will always return without blocking
// See https://github.com/netty/netty/issues/924
int ops = k.interestOps();
ops &= ~SelectionKey.OP_CONNECT;
k.interestOps(ops);
unsafe.finishConnect();
}
} catch (CancelledKeyException e) {
unsafe.close(unsafe.voidPromise());
}
}
红色字体部分，unsafe.read()，进入到AbstractNioByteChannel$NioByteUnsafe，要从io当中读取数据，首先需要分配一个ByteBuf，这里涉及到了2个问题，1、从哪里分配内存，2、每次具体分配多大的内存。首先是第一个问题，首先大家需要了解（allocate和allocateDirect2中方式的不同），具体的实现在 allocator.ioBuffer 当中，会根据平台不同，来决定能否直接分配系统内存。第二个问题，大家可以再看一下 allocHandle.record 方法，这个当中会根据当前从io当中读取的数据量，来决定后续分配内存的大小。然后就是从socket当中读取数据，写入bytebuf，并触发一系列的handler。
public void read() {
final ChannelConfig config = config();
final ChannelPipeline pipeline = pipeline();
final ByteBufAllocator allocator = config.getAllocator();
final int maxMessagesPerRead = config.getMaxMessagesPerRead();
RecvByteBufAllocator.Handle allocHandle = this.allocHandle;
if (allocHandle == null) {
this.allocHandle = allocHandle = config.getRecvByteBufAllocator().newHandle();
}
if (!config.isAutoRead()) {
removeReadOp();
}
ByteBuf byteBuf = null;
int messages = 0;
boolean close = false;
try {
int byteBufCapacity = allocHandle.guess();
int totalReadAmount = 0;
do {
byteBuf = allocator.ioBuffer(byteBufCapacity);
int writable = byteBuf.writableBytes();
int localReadAmount = doReadBytes(byteBuf);
if (localReadAmount <= 0) {
// not was read release the buffer
byteBuf.release();
close = localReadAmount < 0;
break;
}
pipeline.fireChannelRead(byteBuf);
byteBuf = null;
if (totalReadAmount >= Integer.MAX_VALUE - localReadAmount) {
// Avoid overflow.
totalReadAmount = Integer.MAX_VALUE;
break;
}
totalReadAmount = localReadAmount;
if (localReadAmount < writable) {
// Read less than what the buffer can hold,
// which might mean we drained the recv buffer completely.
break;
}
} while ( messages < maxMessagesPerRead);
pipeline.fireChannelReadComplete();
allocHandle.record(totalReadAmount);
if (close) {
closeOnRead(pipeline);
close = false;
}
} catch (Throwable t) {
handleReadException(pipeline, byteBuf, t, close);
}
}
到此，相信大家对“netty server的read流程是怎样的”有了更深的了解，不妨来实际操作一番吧！这里是美国cn2网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！