springboot内置tomcat调优并发线程数解析

protected void countUpOrAwaitConnection() throws InterruptedException {
        if (maxConnections==-1) return;
        LimitLatch latch = connectionLimitLatch;
        if (latch!=null) latch.countUpOrAwait();
    }

/**
     * Allows the server developer to specify the acceptCount (backlog) that
     * should be used for server sockets. By default, this value
     * is 100.
     */
    private int acceptCount = 100;

serverSock.socket().bind(addr,getAcceptCount())

protected void initServerSocket() throws Exception {
        if (!getUseInheritedChannel()) {
            serverSock = ServerSocketChannel.open();
            socketProperties.setProperties(serverSock.socket());
            InetSocketAddress addr = (getAddress()!=null?new InetSocketAddress(getAddress(),getPort()):new InetSocketAddress(getPort()));
            // 核心代码
            serverSock.socket().bind(addr,getAcceptCount());
        } else {
            // Retrieve the channel provided by the OS
            Channel ic = System.inheritedChannel();
            if (ic instanceof ServerSocketChannel) {
                serverSock = (ServerSocketChannel) ic;
            }
            if (serverSock == null) {
                throw new IllegalArgumentException(sm.getString("endpoint.init.bind.inherited"));
            }
        }
        serverSock.configureBlocking(true); //mimic APR behavior
    }

public void createExecutor() {
        internalExecutor = true;
        TaskQueue taskqueue = new TaskQueue();
        TaskThreadFactory tf = new TaskThreadFactory(getName() + "-exec-", daemon, getThreadPriority());
        executor = new ThreadPoolExecutor(getMinSpareThreads(), getMaxThreads(), 60, TimeUnit.SECONDS,taskqueue, tf);
        taskqueue.setParent( (ThreadPoolExecutor) executor);
    }

public void execute(Runnable command) {
        execute(command,0,TimeUnit.MILLISECONDS);
    }

public void execute(Runnable command, long timeout, TimeUnit unit) {
        submittedCount.incrementAndGet();
        try {
        	// 核心代码
            super.execute(command);
        } catch (RejectedExecutionException rx) {
            if (super.getQueue() instanceof TaskQueue) {
                final TaskQueue queue = (TaskQueue)super.getQueue();
                try {
                    if (!queue.force(command, timeout, unit)) {
                        submittedCount.decrementAndGet();
                        throw new RejectedExecutionException("Queue capacity is full.");
                    }
                } catch (InterruptedException x) {
                    submittedCount.decrementAndGet();
                    throw new RejectedExecutionException(x);
                }
            } else {
                submittedCount.decrementAndGet();
                throw rx;
            }
        }
    }

public void execute(Runnable command) {
        if (command == null)
            throw new NullPointerException();
        
        int c = ctl.get();
		// 1、工作线程数小于核心线程数则添加任务，核心线程会处理
        if (workerCountOf(c) < corePoolSize) {
            if (addWorker(command, true))
                return;
            c = ctl.get();
        }
		// 2、工作线程不小于核心线程数，则放到workQueue队列中
        if (isRunning(c) && workQueue.offer(command)) {
            int recheck = ctl.get();
            if (! isRunning(recheck) && remove(command))
                reject(command);
            else if (workerCountOf(recheck) == 0)
                addWorker(null, false);
        }
		// 3、否则添加任务，addWorker会进行创建线程
        else if (!addWorker(command, false))
            reject(command);
    }

public boolean offer(Runnable o) {
        //we can't do any checks
		// parent就是指线程池，没有线程池则添加到队列
        if (parent==null) return super.offer(o);
        //we are maxed out on threads, simply queue the object
		// 线程数量已经达到了最大线程数，那么只能添加到队列
        if (parent.getPoolSize() == parent.getMaximumPoolSize()) return super.offer(o);
        //we have idle threads, just add it to the queue
		// 如果当前处理的任务数量小于当前线程池中线程的数量，那么任务放到线程池，即相当于马上会有空闲线程来处理
        if (parent.getSubmittedCount()<=(parent.getPoolSize())) return super.offer(o);
        //if we have less threads than maximum force creation of a new thread
		// TODO 核心代码，如果当前线程数量还没有达到线程池最大线程池的数量，那么就直接创建线程，这里返回false
        if (parent.getPoolSize()<parent.getMaximumPoolSize()) return false;
        //if we reached here, we need to add it to the queue
		// 最后的策略，放到队列
        return super.offer(o);
    }