自定义线程池（一）核心参数

2024-02-13 18:04:51

核心参数

核心线程数 corePoolSize

如果没有设置允许主线程过期，核心线程数为线程池中保留的最大线程数

最大线程数 maximumPoolSize

线程池能创建的最大工作线程数

线程存活时间 keepAliveTime，时间类型unit

即超过核心线程数的线程过期的时间，在指定时间内未获取到任务的话，则会回收线程。

任务队列 BlockingQueue

存放任务的阻塞队列，符合先进先出原则。有ArrayListBlockingQueue和LinkedBlockQueue两种。

线程工厂 ThreadFactory

创建一个线程工厂，线程池中的线程都由该工厂创建，有统一的线程前缀，可根据不同业务定义，方便定位问题。

拒绝策略 RejectedExecutionHandler

线程超过最大线程数时，线程池对新任务的处理策略，共四种

AbortPolicy（默认）

不接受任务，直接抛出异常

CallerRunsPolicy

由提交任务的线程执行该任务，通常是请求线程执行。不允许任务丢失的业务可以使用该策略

DiscardPolicy

不接受任务，抛弃掉该任务

DiscardOldestPolicy

接受该任务，放弃队列中最早的任务

构造方法共四个（三个重载方法）

//不指定线程工厂和拒绝策略（默认Abort）
public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue) {
        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             Executors.defaultThreadFactory(), defaultHandler);
}
//不指定拒绝策略（默认Abort）
public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory) {
        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             threadFactory, defaultHandler);
}
//不指定线程工厂
public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              RejectedExecutionHandler handler) {
        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             Executors.defaultThreadFactory(), handler);
}
//所有参数
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;
}

使用示例

// 打印线程名
ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(8, 16, 200, 
                 TimeUnit.MILLISECONDS, new LinkedBlockingQueue<>(200), new MyThreadFactory("test-thread-pool-"), new ThreadPoolExecutor.CallerRunsPolicy());
        for (int i = 0; i < 10; i++) {
            threadPoolExecutor.execute(()->{
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("i am " + Thread.currentThread().getName());
            });
        }

输出：

码农公寓