ThreadPoolExecutor继承AbstractExecutorService;AbstractExecutorService实现ExecutorService;ExecutorService继承Executor类
ThreadPoolExecutor有4个构造函数
-
corePoolSize
核心线程数,默认初始时为0,调用prestartAllCoreThreads()或prestartCoreThreads()预启动即没有任务时就创建corePoolSize线程
int maximumPoolSize 最大线程数,线程池中最多能创建的线程数量 -
keepAliveTime 没有任务时最多保留多久时间终止
-
TimeUnit unit
keepAliveTime的时间单位,keepAliveTime的时间单位,
有7种TimeUnit.DAYS(天),
TimeUnit.HOURS(时),
TimeUnit.MINUTES(分),
TimeUnit.SECONDS(秒),
TimeUnit.MILLISECONDS(毫秒),
TimeUnit.MICROSECONDS(微秒),
TimeUnit.NANOSECONDS(纳秒) -
BlockingQueue workQueue
堵塞队列,用来执行等待任务
有以下几种:arrayBlockingQueue 有界队列,初始化时需要指定队列大小(FIFO先进先出)
linkedBlockingQueue 无界队列,队列大小与maximumPoolSize无关(FIFO先进先出)
sysnchronousQueue 直接移交,不保存提交的任务,而是将直接新建一个线程来执行新来的任务 -
threadFactory
创建线程的工厂 默认Executors.defaultThreadFactory() -
Handler
拒绝处理任务时的策略 默认defaultHandler=new AbortPolicy()
有4种拒绝策略:
ThreadPoolExecutor.AbortPolicy:丢弃任务并抛出RejectedExecutionException异常。
ThreadPoolExecutor.DiscardPolicy:也是丢弃任务,但是不抛出异常。
ThreadPoolExecutor.DiscardOldestPolicy:丢弃队列最前面的任务,然后重新尝试执行任务(重复此过程)
ThreadPoolExecutor.CallerRunsPolicy:由调用线程处理该任务 -
提交任务
execute() 参数为Runnable,没有返回值,用来执行传入的任务
submit()在AbstractExecutorService中有具体实现,没在ThreadPoolExecutor进行重新,返回Future<?>,底层实际上也调用execute() -
关闭线程
当创建线程池后,初始时,线程池处于RUNNING状态;
private static final int RUNNING = -1 << COUNT_BITS;
private static final int SHUTDOWN = 0 << COUNT_BITS;
private static final int STOP = 1 << COUNT_BITS;
private static final int TIDYING = 2 << COUNT_BITS;
private static final int TERMINATED = 3 << COUNT_BITS;
pool.shutdown():调用shutdown()后,线程状态处于SHUTDOWN状态,线程池不接受新的任务,等待所有任务执行完毕
pool.shutdownNow():调用shutdownNow()后,线程处于STOP状态,线程不接受新的任务,尝试终止正在执行的任务,并且返回等待任务列表
当等待队列和线程池为空时为TIDYING状态/线程池为空时为TIDYING状态(STOP -> TIDYING、SHUTDOWN -> TIDYING)
当线程池处于SHUTDOWN或STOP状态,并且所有工作线程已经销毁,任务缓存队列已经清空或执行结束后,线程池被设置为TERMINATED状态
package thread;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
public class ThreadPoolExcutorDemo {
public static void main(String[] args) {
//等待线程队列
ArrayBlockingQueue<Runnable> workQueue=new ArrayBlockingQueue<Runnable>(5);
ThreadPoolExecutor pool=new ThreadPoolExecutor(5, 10, 200, TimeUnit.MILLISECONDS, workQueue);
for (int i = 0; i < 15; i++) {
MyTask myTask=new MyTask(i);
pool.execute(myTask);
System.out.println("线程池线程数量:"+pool.getPoolSize()+",队列中等待线程数:"+pool.getQueue().size()+",已执行完线程数量:"+pool.getCompletedTaskCount());
}
System.out.println(pool.isShutdown());
pool.shutdown();
System.out.println(pool.isShutdown());
System.out.println(pool.isTerminated());
}
}
class MyTask implements Runnable{
public int taskNum;
public MyTask(int num){
this.taskNum=num;
}
@Override
public void run() {
System.out.println("正在执行task"+taskNum);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("任务task"+taskNum+"执行完毕");
}
}