java – 如何实现任务调度？

处理事件的线程将轮询该队列中的项目并处理它们.看看头部项目,看看下一个事件何时需要运行.选择一个对象用作锁定对象,让主线程在该对象上调用Object.wait(long),将该方法传递给毫秒,直到需要运行下一个事件.

如果有新线程进入,请将其添加到适当位置的队列中.如果项目位于队列的头部,这意味着线程需要更快地唤醒.在锁定对象上调用Object.notifyAll()以唤醒处理线程.它将看到没有任何东西可以处理并在适当的时间内重新入睡.

public class ProcessingQueue extends Thread {

  private PriorityQueue<Task> tasks;  

  private volatile boolean isRunning = true;

  public void addTask(Task t) {
    synchronized (this.tasks) {
      this.tasks.offer(t);
      // this call requires synchronization to this.tasks
      this.tasks.notifyAll();
    }
  }

  public void shutdown() {
    this.isRunning = false;
    synchronized (this.tasks) {
      this.notifyAll();
    }
  }

  public void run() {
    while (this.isRunning) {
      synchronized (this.tasks) {
        Task t = this.tasks.peek();
        // by default,if there are no tasks,this will wake every 60 seconds
        long millisToSleep = 60000;
        // getExecuteMillis() should return the time,in milliseconds,for execution
        if (t != null) millisToSleep = t.getExecuteMillis() - System.currentTimeMillis();
        if (millisToSleep > 0) {
          try {
            // this line requires synchronization to this.tasks
            // and the lock is removed while it waits
            this.tasks.wait(millisToSleep);
          } catch (InterruptedException e) {
          }
        }
        t = this.tasks.poll();
        if (t != null) {
          t.execute();
        }
      }
    }
  }
}