netty应用退出

netty程序，使用shutdownGracefully退出。退出前会把队列中的消息发送完，释放channel，多路复用器的去注册，清空定时器任务等。

    public Future<?> shutdownGracefully(long quietPeriod, long timeout, TimeUnit unit) {
        EventExecutor[] var6 = this.children;
        int var7 = var6.length;

        for(int var8 = 0; var8 < var7; ++var8) {
            EventExecutor l = var6[var8];
            l.shutdownGracefully(quietPeriod, timeout, unit);
        }

        return this.terminationFuture();
    }

shutdownGracefully实现在NioEventLoop的父类SingleThreadEventExecutor中，

首先是改变state，为了防止并发问题，这里是netty 4,采用的原子类自旋的方式避免加锁。

public Future<?> shutdownGracefully(long quietPeriod, long timeout, TimeUnit unit) {
        ObjectUtil.checkPositiveOrZero(quietPeriod, "quietPeriod");
        if(timeout < quietPeriod) {
            throw new IllegalArgumentException("timeout: " + timeout + " (expected >= quietPeriod (" + quietPeriod + "))");
        } else {
            ObjectUtil.checkNotNull(unit, "unit");
            if(this.isShuttingDown()) {
                return this.terminationFuture();
            } else {
                boolean inEventLoop = this.inEventLoop();

                boolean wakeup;
                int oldState;
                int newState;
                do {
                    if(this.isShuttingDown()) {
                        return this.terminationFuture();
                    }

                    wakeup = true;
                    oldState = this.state;
                    if(inEventLoop) {
                        newState = 3;
                    } else {
                        switch(oldState) {
                        case 1:
                        case 2:
                            newState = 3;
                            break;
                        default:
                            newState = oldState;
                            wakeup = false;
                        }
                    }
                } while(!STATE_UPDATER.compareAndSet(this, oldState, newState));

                this.gracefulShutdownQuietPeriod = unit.toNanos(quietPeriod);
                this.gracefulShutdownTimeout = unit.toNanos(timeout);
                if(this.ensureThreadStarted(oldState)) {
                    return this.terminationFuture;
                } else {
                    if(wakeup) {
                        this.taskQueue.offer(WAKEUP_TASK);
                        if(!this.addTaskWakesUp) {
                            this.wakeup(inEventLoop);
                        }
                    }

                    return this.terminationFuture();
                }
            }
        }
    }

唤醒selector,由NioEventLoop实现。

 protected void wakeup(boolean inEventLoop) {
        if(!inEventLoop && this.nextWakeupNanos.getAndSet(-1L) != -1L) {
            this.selector.wakeup();
        }

    }

状态改变之后， run方法中检测到状态变化，执行closeAll方法

if(this.isShuttingDown()) {
                        this.closeAll();
                        if(this.confirmShutdown()) {
                            return;
                        }
                    }