重入锁条件

Question

I wanted to create class Suspender that allows to pause and resume threads anytime you want, but unfortunately nothing happened after calling condition.signalAll() . Can someone tell me, what is the reason?

public class Task extends Thread{

    private Suspender suspender;

    public boolean paused = false;

    public Task(Suspender suspender){
        this.suspender = suspender;
    }

    public void resumeThread(){
        suspender.resume(this);
    }

    public void run(){
        System.out.println("Pausing");
        paused = true;
        suspender.pause(this);
        System.out.println("Resumed");
    }
}

public class Suspender{

    private ReentrantLock lock = new ReentrantLock();
    private Condition condition = lock.newCondition();

    public void pause(Task current) {
        try{
            lock.lock();
            while(current.paused){
                condition.await();
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally{
            lock.unlock();
        }
    }

    public void resume(Task current) {
        try{
            lock.lock();
            current.paused = false;
            condition.signalAll();
        }finally{
            lock.unlock();
        }
    }

}

public class Start{

    public static void main(String args[]) throws Exception {
        Suspender suspender = new Suspender();

        Task t1 = new Task(suspender), t2 = new Task(suspender);
        t1.start();
        t2.start();

        TimeUnit.SECONDS.sleep(2);
        t1.resume();
        TimeUnit.SECONDS.sleep(2);
        t2.resumeThread();

        t2.join();
    }

}

Answer 1

Your main thread calls t1.resume() , but your Task class declares public void resume(Task current) . Those are two different methods. Java allows different methods to have the same name if they have different argument lists. When your main thread calls t1.resume() it is calling a deprecated method of the Thread class , which will have no effect because the thread never was suspended.*

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* Note: suspended is not the same thing as awaiting a condition.