ThreadPoolExecutor线程池内部处理浅析 - ToB企服应用市场:ToB评测及商务社交产业平台

// 设置线程池时指定核心线程数、最大线程数、线程存活时间及等待队列。
// 线程创建工厂和拒绝策略使用默认的（AbortPolicy）
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue) {
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
Executors.defaultThreadFactory(), defaultHandler);
}
// 设置线程池时指定核心线程数、最大线程数、线程存活时间、等待队列及线程创建工厂
// 拒绝策略使用默认的（AbortPolicy）
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
ThreadFactory threadFactory) {
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
threadFactory, defaultHandler);
}
// 设置线程池时指定核心线程数、最大线程数、线程存活时间、等待队列及拒绝策略
// 线程创建工厂使用默认的
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
RejectedExecutionHandler handler) {
this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
Executors.defaultThreadFactory(), handler);
}
// 设置线程池时指定核心线程数、最大线程数、线程存活时间、等待队列、线程创建工厂及拒绝策略
public ThreadPoolExecutor(int corePoolSize,
int maximumPoolSize,
long keepAliveTime,
TimeUnit unit,
BlockingQueue<Runnable> workQueue,
ThreadFactory threadFactory,
RejectedExecutionHandler handler) {
if (corePoolSize < 0 ||
maximumPoolSize <= 0 ||
maximumPoolSize < corePoolSize ||
keepAliveTime < 0)
throw new IllegalArgumentException();
if (workQueue == null || threadFactory == null || handler == null)
throw new NullPointerException();
this.acc = System.getSecurityManager() == null ?
null :
AccessController.getContext();
this.corePoolSize = corePoolSize;
this.maximumPoolSize = maximumPoolSize;
this.workQueue = workQueue;
this.keepAliveTime = unit.toNanos(keepAliveTime);
this.threadFactory = threadFactory;
this.handler = handler;
}

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public void execute(Runnable command) {
// 判断提交的任务command是否为null，若是null，则抛出空指针异常；
if (command == null)
throw new NullPointerException();
// 获取线程池中当前线程数
int c = ctl.get();
// 如果线程池中当前线程数小于核心池大小，进入if语句块
if (workerCountOf(c) < corePoolSize) {
// 如果以给定的命令启动一个核心线程执行任务成功，直接返回
if (addWorker(command, true))
return;
c = ctl.get();
}
// 如果当前线程池处于RUNNING状态，则将任务放入任务缓存队列
if (isRunning(c) && workQueue.offer(command)) {
int recheck = ctl.get();
// 如果线程池不处于运行状态并且移除刚加入的任务成功则执行拒绝策略
if (! isRunning(recheck) && remove(command))
reject(command);
// 如果当前线程数为0，则在线程池里增加一个线程，保证队列里的任务不会没有线程执行
else if (workerCountOf(recheck) == 0)
addWorker(null, false);
}
// 尝试启动核心线程之外的线程，如果不满足，则执行对应的拒绝策略
else if (!addWorker(command, false))
reject(command);
}

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