Java：在当前运行时不要启动另一个线程

Question

I have main thread with method "start". This method starts another thread, that doing long job. Method "start" can be call from another threads. How to avoid creating new threads in "start" method if already have one running and do not lock main thread? I trying use singleThreadExecutor, but it queues tasks.

code: Start method:

 public void start(){
// need only one active thread
// if thread alive, avoid to start another
        t = new Thread( new Runnable() {
            public void run() {
                try {
                    Thread.currentThread().sleep(3000);     
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        t.start();      
    }

Simple test

    for (int i = 0; i < 100; i++) {
            Thread r = new Thread( new Runnable() {
                public void run() {
                    Helper.getInstance().start();
                }
            });
            r.start();      
   }    

Answer 1

如果只想在当前线程繁忙时丢弃新任务，则可以使用SingleThreadExecutor并将其配置为丢弃所有溢出任务，而不是对其进行排队。