超出最大许可数:信号量

Question

public class semaphoreTest {

static LinkedList<Integer> integerLinkedList = new LinkedList<>();
static Semaphore semaphore = new Semaphore(1);
static Object lock = new Object();

public static void main(String[] args) throws InterruptedException {
    Thread t1 = new Thread(new Runnable() {
        @Override
        public void run() {
            try {
                produce();
            } catch (InterruptedException e) {
            }
        }
    });

    Thread t2 = new Thread(new Runnable() {
        @Override
        public void run() {
            try {
                consume();
            } catch (InterruptedException e) {
            }
        }
    });

    t1.start();
    t2.start();

    t1.join();
    t2.join();

}


private static void produce() throws InterruptedException {
    semaphore.acquire();
    int value = 0;
    while (true) {
        while (integerLinkedList.size() == 10) {
            semaphore.release();
        }

        integerLinkedList.add(value++);


    }

}

private static void consume() throws InterruptedException {
    semaphore.acquire();
    while (true) {
        while (integerLinkedList.size() == 0) {
            semaphore.release();
        }
        //semaphore.release();
        Integer value = integerLinkedList.removeFirst();
        System.out.println("Size of the List is " + integerLinkedList.size() + " and value removed is " + value);
        semaphore.release();

        Thread.sleep(100);
    }
}


}

这是我试图用信号量作为锁写的生产者消费者问题.但我差不多删除了240个元素之后就无法弄清楚它会给出错误信息Maximum permit count exceeded.

我在正确的地方释放锁,但无法弄清楚它的获取部分有什么问题.

错误消息如下:

Exception in thread "Thread-0" java.lang.Error: Maximum permit count exceeded
at java.util.concurrent.Semaphore$Sync.tryReleaseShared(Semaphore.java:192)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.releaseShared(AbstractQueuedSynchronizer.java:1341)
at java.util.concurrent.Semaphore.release(Semaphore.java:426)
at interviewQuestions.semaphoreTest.procude(semaphoreTest.java:53)
at interviewQuestions.semaphoreTest.access$000(semaphoreTest.java:12)
at interviewQuestions.semaphoreTest$1.run(semaphoreTest.java:23)
at java.lang.Thread.run(Thread.java:745)
Exception in thread "Thread-1" java.lang.Error: Maximum permit count exceeded
at java.util.concurrent.Semaphore$Sync.tryReleaseShared(Semaphore.java:192)
at java.util.concurrent.locks.AbstractQueuedSynchronizer.releaseShared(AbstractQueuedSynchronizer.java:1341)
at java.util.concurrent.Semaphore.release(Semaphore.java:426)
at interviewQuestions.semaphoreTest.consume(semaphoreTest.java:72)
at interviewQuestions.semaphoreTest.access$100(semaphoreTest.java:12)
at interviewQuestions.semaphoreTest$2.run(semaphoreTest.java:33)
at java.lang.Thread.run(Thread.java:745)

Answer 1

问题是你释放信号量的次数多于获得的信号量.您应该删除while以释放您的信号量.你应该只发布一次,所以请if改用.

并根据您的计划produce(),consume()应该改为这个.

生产()

private static void produce() throws InterruptedException {       
    int value = 0;      

    while (true) {
        //try to get control & put an item.
        semaphore.acquire();

        //but if the queue is full, give up and try again.
        if (integerLinkedList.size() == 10) {
            semaphore.release();
            continue;
        }

        //if not full, put an item & release the control.
        integerLinkedList.add(value++);
        semaphore.release();

    }

}

消耗()

private static void consume() throws InterruptedException {        
    while (true) {
        //try to get the control and consume an item.
        semaphore.acquire();

        //but if the queue is empty, give up and try again.
        if (integerLinkedList.size() == 0) {
            semaphore.release();
            continue;
        }

        //if not empty, *consume first one, *print it, *release the control and go sleep.
        Integer value = integerLinkedList.removeFirst();
        System.out.println("Size of the List is " + integerLinkedList.size() + " and value removed is " + value);

        semaphore.release();    
        Thread.sleep(100);
    }
}

如果你希望在更安全的一面,你可以Thread.sleep(50);在每个break;语句之前添加一些东西,这样你就可以给另一个线程继续执行它.

我假设您编写了典型的生产者消费者问题.如果您想让我改变一下,请告诉我.无论如何希望这可以解决你的基本问题.:))