- java预定义的四种线程池
- SingleThreadExexcutor：单线程数的线程池
- FixedThreadPool：固定线程数的线程池
- CacheThreadPool：可缓存的线程池
- ScheduledThreadPoo：支持定时或周期任务的线程池
这四种线程池都有各自问题，建议自定义线程池类（继承ThreadPoolExecutor），使用自定义的线程池，这样能对各个线程池参数都熟悉，避免使用过程中出错
- 四种线程池源码
上面四种线程池类都继承ThreadPoolExecutor，在创建时都是直接返回new ThreadPoolExecutor(参数)，不同的是定义的ThreadPoolExecutor(参数)中参数不同，而ThreadPoolExecutor又继承ExecutorService类
(1)FixedThreadPool
(2)CacheThreadPool
(3)SingleThreadExecutor
上面代码神似new FixedThreadPoop(1)，但又有区别，因为外面多了一层FinalizableDelegatedExecutorService，其作用如下：
可知，FixedThreadPoop可以向下转换，然后重新对其线程池进行配置参数【派变=(强转)基变，派变的范围大，向下转换即转为范围大的对象，简称“吓大”】，但SingleThreadExecutor不可以向下转换，故SingleThreadExecutor被创建后，无法再修改其线程池参数，真正地做到single单个线程。
（4）ScheduledThreadPool
public static ScheduledExecutorService new ScheduledThreadPool(int corePoolSize)
{ return new ScheduledThreadPoolExecutor(corePoolSize);
}其中ScheduledThreadPoolExecutor继承了ThreadPoolExecutor，故new ScheduledThreadPoolExecutor(corePoolSize)还是返回了父类构造new ThreadPoolExecutor();
- 自定义线程池
- ThreadPoolExecutor构造方法
其参数解释:
- 自定义线程池
使用了有界队列，并自定义线程创建工厂ThreadFactory和拒绝策略handler
public class ThreadTest {public static void main(String[] args) throws InterruptedException, IOException {int corePoolSize = 2;int maximumPoolSize = 4;long keepAliveTime = 10;
TimeUnit unit = TimeUnit.SECONDS;
BlockingQueue<Runnable> workQueue = new ArrayBlockingQueue<>(2);
ThreadFactory threadFactory = new NameTreadFactory();
RejectedExecutionHandler handler = new MyIgnorePolicy();
ThreadPoolExecutor executor = new ThreadPoolExecutor(corePoolSize, maximumPoolSize, keepAliveTime, unit,
workQueue, threadFactory, handler);
executor.prestartAllCoreThreads(); // 预启动所有核心线程 for (int i = 1; i <= 10; i++) {
MyTask task = new MyTask(String.valueOf(i));
executor.execute(task);
}
System.in.read(); //阻塞主线程 }static class NameTreadFactory implements ThreadFactory {private final AtomicInteger mThreadNum = new AtomicInteger(1);
@Overridepublic Thread newThread(Runnable r) {
Thread t = new Thread(r, "my-thread-" + mThreadNum.getAndIncrement());
System.out.println(t.getName() + " has been created");return t;
}
}public static class MyIgnorePolicy implements RejectedExecutionHandler {public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
doLog(r, e);
}private void doLog(Runnable r, ThreadPoolExecutor e) {// 可做日志记录等System.err.println( r.toString() + " rejected");// System.out.println("completedTaskCount: " + e.getCompletedTaskCount()); }
}static class MyTask implements Runnable {private String name;public MyTask(String name) {this.name = name;
}
@Overridepublic void run() {try {
System.out.println(this.toString() + " is running!");
Thread.sleep(3000); //让任务执行慢点} catch (InterruptedException e) {
e.printStackTrace();
}
}public String getName() {return name;
}
@Overridepublic String toString() {return "MyTask [name=" + name + "]";
}
}
}运行结果：
其中7-10号线程被拒绝策略拒绝了，1、2号线程执行完后，3、6号线程进入核心线程池执行，此时4、5号线程在任务队列等待执行，3、6线程执行完再通知4、5线程执行
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