netty源码解析(4.0)-17 ChannelHandler: IdleStateHandler实现

   io.netty.handler.timeout.IdleStateHandler功能是监测Channel上read, write或者这两者的空闲状态。当Channel超过了指定的空闲时间时,这个Handler会触发一个IdleStateEvent事件。

  在第一次检测到Channel变成active状态时向EventExecutor中提交三个延迟任务:

    ReaderIdleTimeoutTask: 检测read空闲超时。

    WriterIdleTimeoutTask: 检测write空闲超时。

    AllIdleTimeoutTask: 检测所有的空闲超时。

  任何一个延迟任务检测到空闲超时是会触发一个IdleStateEvent。无论如何,延迟任务都会再次把自己提交到EventExecutor中,等待下次执行。

  三个延迟任务对应于三个超时时间,都是可以独立设置的:

 1 public IdleStateHandler(boolean observeOutput,
 2             long readerIdleTime, long writerIdleTime, long allIdleTime,
 3             TimeUnit unit) {
 4         if (unit == null) {
 5             throw new NullPointerException("unit");
 6         }
 7 
 8         this.observeOutput = observeOutput;
 9 
10         if (readerIdleTime <= 0) {
11             readerIdleTimeNanos = 0;
12         } else {
13             readerIdleTimeNanos = Math.max(unit.toNanos(readerIdleTime), MIN_TIMEOUT_NANOS);
14         }
15         if (writerIdleTime <= 0) {
16             writerIdleTimeNanos = 0;
17         } else {
18             writerIdleTimeNanos = Math.max(unit.toNanos(writerIdleTime), MIN_TIMEOUT_NANOS);
19         }
20         if (allIdleTime <= 0) {
21             allIdleTimeNanos = 0;
22         } else {
23             allIdleTimeNanos = Math.max(unit.toNanos(allIdleTime), MIN_TIMEOUT_NANOS);
24         }
25     }

  这个类继承自io.netty.channel.ChannelDuplexHandler, 它是一个有状态的ChannelHandler, 定义了三个状态:

  private byte state; // 0 - none, 1 - initialized, 2 - destroyed

  state属性保存了它的状态。0:初始状态,1:已经初始化, 2: 已经销毁。

  这个ChannelHandler被加入到Channel的pipeline中之后,在Channel已经被register到EventLoop中,且处于Active状态时,会执行一次初始化操作,向EventExecutor提交前面提到的三个延迟任务。这初始化操作在initialize方法中实现。

 1     private void initialize(ChannelHandlerContext ctx) {
 2         // Avoid the case where destroy() is called before scheduling timeouts.
 3         // See: https://github.com/netty/netty/issues/143
 4         switch (state) {
 5         case 1:
 6         case 2:
 7             return;
 8         }
 9 
10         state = 1;
11         initOutputChanged(ctx);
12 
13         lastReadTime = lastWriteTime = ticksInNanos();
14         if (readerIdleTimeNanos > 0) {
15             readerIdleTimeout = schedule(ctx, new ReaderIdleTimeoutTask(ctx),
16                     readerIdleTimeNanos, TimeUnit.NANOSECONDS);
17         }
18         if (writerIdleTimeNanos > 0) {
19             writerIdleTimeout = schedule(ctx, new WriterIdleTimeoutTask(ctx),
20                     writerIdleTimeNanos, TimeUnit.NANOSECONDS);
21         }
22         if (allIdleTimeNanos > 0) {
23             allIdleTimeout = schedule(ctx, new AllIdleTimeoutTask(ctx),
24                     allIdleTimeNanos, TimeUnit.NANOSECONDS);
25         }
26     }

 

  第4-10行,只有处于初始状态时才执行后面的操作,避免多次提交定时任务。

  第11行, 初始化对对Channel的outboundBuffer变化的监视,只有当observeOutput属性设置为true时才开启这个监视。

  第13-25行,分别提交三个延迟任务。

 

  initialize方法可能在三个地方被调用:

    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        if (ctx.channel().isActive() && ctx.channel().isRegistered()) {
            // channelActive() event has been fired already, which means this.channelActive() will
            // not be invoked. We have to initialize here instead.
            initialize(ctx);
        } else {
            // channelActive() event has not been fired yet.  this.channelActive() will be invoked
            // and initialization will occur there.
        }
    }

    @Override
    public void channelRegistered(ChannelHandlerContext ctx) throws Exception {
        // Initialize early if channel is active already.
        if (ctx.channel().isActive()) {
            initialize(ctx);
        }
        super.channelRegistered(ctx);
    }


    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        // This method will be invoked only if this handler was added
        // before channelActive() event is fired.  If a user adds this handler
        // after the channelActive() event, initialize() will be called by beforeAdd().
        initialize(ctx);
        super.channelActive(ctx);
    }

 

  如果在Channel初始化的时候把这个Handler添加到pipeline中,那么这个Handler的channelActive方法一定会被调用,只需要在channleActive中调用initialize就可以打了。但是Handler可以在任何时候被加入到pipleline中。当ChannelHandler被添加到pipeline中时,Channel可能已经被register到EventLoop中,且已经处于Active状态,这种情况下,channelRegistered和channelActive方法都不会被调用,所以必须在handlerAdded中调用initialize。如果此时,Channnel已经处于Active状态,但还没被注册到EventLoop,只能在channelRegisted中调用initialize。

  

  初始化完成之后,延迟任务到期执行时会把自己再次提交到EventExecutor中,等待下次执行。同时会检查是否满足触发事件的条件,如果是就触发一条自定义的事件。

  

read空闲超时检查

 1 private final class ReaderIdleTimeoutTask extends AbstractIdleTask {
 2         @Override
 3         protected void run(ChannelHandlerContext ctx) {
 4             long nextDelay = readerIdleTimeNanos;
 5             if (!reading) {
 6                 nextDelay -= ticksInNanos() - lastReadTime;
 7             }
 8 
 9             if (nextDelay <= 0) {
10                 // Reader is idle - set a new timeout and notify the callback.
11                 readerIdleTimeout = schedule(ctx, this, readerIdleTimeNanos, TimeUnit.NANOSECONDS);
12 
13                 boolean first = firstReaderIdleEvent;
14                 firstReaderIdleEvent = false;
15 
16                 try {
17                     IdleStateEvent event = newIdleStateEvent(IdleState.READER_IDLE, first);
18                     channelIdle(ctx, event);
19                 } catch (Throwable t) {
20                     ctx.fireExceptionCaught(t);
21                 }
22             } else {
23                 // Read occurred before the timeout - set a new timeout with shorter delay.
24                 readerIdleTimeout = schedule(ctx, this, nextDelay, TimeUnit.NANOSECONDS);
25             }
26         }
27     }

  4-9行,判断是否read空闲超时。

  11-21行,read空闲超时,重新把自己提交成延迟任务。

  24行,read没有空闲超时,重新把自己提交成延迟任务。

  这里的关键是判断read空闲超时。lastReadTime是最近一次执行read的时间,readerIdleTimeNanos是初始化时设置的空闲超时时间,因此如果readerIdleTimeNanos - (ticksInNanos() - lastReadtime)  <= 0,表示已经read空闲超时了。令人困惑的是第5行,只有在reading==false才检查进行空闲超时的计算。笔者在<<netty源码解解析(4.0)-14 Channel NIO实现:读取数据>>一章中分析过Channel read的实现。一次read操作或触发多个read和一个readComplete事件,read操作由多个步骤组成。这reading属性用来表示正在read的状态。

 1     @Override
 2     public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
 3         if (readerIdleTimeNanos > 0 || allIdleTimeNanos > 0) {
 4             reading = true;
 5             firstReaderIdleEvent = firstAllIdleEvent = true;
 6         }
 7         ctx.fireChannelRead(msg);
 8     }
 9 
10     @Override
11     public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
12         if ((readerIdleTimeNanos > 0 || allIdleTimeNanos > 0) && reading) {
13             lastReadTime = ticksInNanos();
14             reading = false;
15         }
16         ctx.fireChannelReadComplete();
17     }

  3-4行,在设置了读空闲超时或所有空闲超时的情况下,会吧reading设置成true,表示当前正处于正在read的状态。

  12-14行,在设置了读空闲超时或所有空闲超时的情况下, 如果当前正处于read状态,把reading设置成false,同时更新最近一次执行read的时间。

 

write空闲超时检查

 1     private final class WriterIdleTimeoutTask extends AbstractIdleTask {
 2 
 3         @Override
 4         protected void run(ChannelHandlerContext ctx) {
 5 
 6             long lastWriteTime = IdleStateHandler.this.lastWriteTime;
 7             long nextDelay = writerIdleTimeNanos - (ticksInNanos() - lastWriteTime);
 8             if (nextDelay <= 0) {
 9                 // Writer is idle - set a new timeout and notify the callback.
10                 writerIdleTimeout = schedule(ctx, this, writerIdleTimeNanos, TimeUnit.NANOSECONDS);
11 
12                 boolean first = firstWriterIdleEvent;
13                 firstWriterIdleEvent = false;
14 
15                 try {
16                     if (hasOutputChanged(ctx, first)) {
17                         return;
18                     }
19 
20                     IdleStateEvent event = newIdleStateEvent(IdleState.WRITER_IDLE, first);
21                     channelIdle(ctx, event);
22                 } catch (Throwable t) {
23                     ctx.fireExceptionCaught(t);
24                 }
25             } else {
26                 // Write occurred before the timeout - set a new timeout with shorter delay.
27                 writerIdleTimeout = schedule(ctx, this, nextDelay, TimeUnit.NANOSECONDS);
28             }
29         }
30     }

 

  6-8行,检查write空闲超时,和检查read空闲超时类似。

  12-21行,如果write空闲超时,且outboundBuffer中的数据没有变化, 触发write空闲超时事件。

  这里调用了hasOutputChanged方法检查outboundBuffer中的数据是否有变化。笔者在<<netty源码解解析(4.0)-15 Channel NIO实现:写数据>>中分write实现时,已经讲过,每个Channel都以一个outboundBuffer, write的数据会先序列化成Byte流追加到outboundBuffer中,然后再从outboundBuffer中顺序读出Byte流执行真正的write操作。在Handler的write方法没有被调用的情况下,如果outboundBuffer中有数据,且数据发送了变化,表示正在执行真正的write操作,反之则意味着Channel处于不可写的状态,无法执行真正的write操作。write空闲超时事件只会在write空闲超时且没有执行真正write操作的时候才会触发。另外,这个检查有个开关属性,只有observeOutput==true时才会检查。

  

  AllIdleTimeoutTask的实现和WriterIdleTimeoutTask类似,只不过检查超时的条件有些差别:read和write任何一个空闲超时都算超时。

 

ReadTimeoutHandler实现

  ReadTimeoutHandler继承了IdleStateHandler类,它的功能是在触发read空闲超时事件时触发一个ReadTimeoutException异常,同时关闭Channel。 

    @Override
    protected final void channelIdle(ChannelHandlerContext ctx, IdleStateEvent evt) throws Exception {
        assert evt.state() == IdleState.READER_IDLE;
        readTimedOut(ctx);
    }

    /**
     * Is called when a read timeout was detected.
     */
    protected void readTimedOut(ChannelHandlerContext ctx) throws Exception {
        if (!closed) {
            ctx.fireExceptionCaught(ReadTimeoutException.INSTANCE);
            ctx.close();
            closed = true;
        }
    }

 

 

WriteTimeoutHandler实现

  WriteTimeoutHandler继承了ChannelOutboundHandlerAdapter,它的功能是在触发监视Channel的write调用超时,如果超时则关闭掉这个Channel。和ReadTimeoutHandler不同,它监控的不是空闲超时,而是Channel的write方法返回的Promise超时。

  首先在write时候,为每个Promise添加一个监控超时的延迟任务:

    @Override
    public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
        scheduleTimeout(ctx, promise);
        ctx.write(msg, promise);
    }
    private void scheduleTimeout(final ChannelHandlerContext ctx, final ChannelPromise promise) {
        // Schedule a timeout.
        final WriteTimeoutTask task = new WriteTimeoutTask(ctx, promise);
        task.scheduledFuture = ctx.executor().schedule(task, timeoutNanos, TimeUnit.NANOSECONDS);

        if (!task.scheduledFuture.isDone()) {
            addWriteTimeoutTask(task);

            // Cancel the scheduled timeout if the flush promise is complete.
            promise.addListener(task);
        }
    }

   然后,如果延迟任务执行的时候检查到Promise超时,就触发一个WriteTimeoutException异常,然后关闭掉这个Channel。

    protected void writeTimedOut(ChannelHandlerContext ctx) throws Exception {
        if (!closed) {
            ctx.fireExceptionCaught(WriteTimeoutException.INSTANCE);
            ctx.close();
            closed = true;
        }
    }

   WriteTimeoutTask类同时实现了Runnable和ChannelFutureListener接口,超时后会调用run方法。

 1         @Override
 2         public void run() {
 3             // Was not written yet so issue a write timeout
 4             // The promise itself will be failed with a ClosedChannelException once the close() was issued
 5             // See https://github.com/netty/netty/issues/2159
 6             if (!promise.isDone()) {
 7                 try {
 8                     writeTimedOut(ctx);
 9                 } catch (Throwable t) {
10                     ctx.fireExceptionCaught(t);
11                 }
12             }
13             removeWriteTimeoutTask(this);
14         }

  7-10行,promise没有完成,触发WriteTimeoutException或其他异常。

      13行,write已经完成,删除当前的WriteTimeoutTask对象。

    如果promise已经完成, 会调用operationComplete方法, 清理掉当前的WriteTimeoutTask对象。

        @Override
        public void operationComplete(ChannelFuture future) throws Exception {
            // scheduledFuture has already be set when reaching here
            scheduledFuture.cancel(false);
            removeWriteTimeoutTask(this);
        }

   

  

posted on 2019-08-14 15:34  自带buff  阅读(...)  评论(...编辑  收藏

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