具有指定线程的Java信号量增量计数

Question

有没有人知道为什么在编译这段代码后，（我认为）还有一个线程在等待什么？ 我想用ID为10,11和12的线程逐一增加计数，直到50。 最后，它工作，但红色按钮（终止）仍然是红色，这意味着它仍在运行的程序，可能还在等待一些东西。

我认为当计数为50时，返回应该起作用并退出方法。也许它确实如此，但还不够。

以下是代码：

public class App12 {

    Semaphore sem1 = new Semaphore(1);
    Semaphore sem2 = new Semaphore(0);
    Semaphore sem3 = new Semaphore(0);

    int count = 0;

    public void inc() throws InterruptedException {

        while (true) {
            if (Thread.currentThread().getId() == 10) {
                sem1.acquire();
                if (count != 50) {
                    count++;
                    System.out.println("Thread" + Thread.currentThread().getId() + " has incremented " + count);

                    sem2.release();
                } else
                    return;
            }

            if (Thread.currentThread().getId() == 11) {
                sem2.acquire();
                if (count != 50) {
                    count++;
                    System.out.println("Thread" + Thread.currentThread().getId() + " has incremented " + count);

                    sem3.release();
                } else
                    return;

            }

            if (Thread.currentThread().getId() == 12) {
                sem3.acquire();
                if (count != 50) {
                    count++;
                    System.out.println("Thread" + Thread.currentThread().getId() + " has incremented " + count);

                    sem1.release();
                } else
                    return;

            }
        }
    }

    public static void main(String[] args) {

        App12 ap = new App12();
        for (int i = 0; i < 3; i++) {
            Thread th1 = new Thread(new Runnable() {
                public void run() {
                    try {
                        ap.inc();
                        // dec3();

                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }

                }
            });
            th1.start();

        }
    }
}

Answer 1

你的问题是你永远不会释放线程上的锁，他们最终会永远等待。

根据您的逻辑，线程A版本B发布C.

但是，一旦你达到50，线程A就会返回。永远不要释放线程B和C.

所以你需要的是一个退出条件释放所有其他等待线程。

例如（在你的while循环中）：

if(count == 50) {
                sem2.release();
                sem3.release();
                sem1.release();
            }

问题是，一旦11或12增加，他们就会再次进入循环，此时他们会锁定等待被释放的宿舍。如果您的计数为50，则释放它的线程将返回，而不会输入您的if条件。

或者，您应该能够在else子句中添加一个版本，因此所有线程都会被释放。

希望有所帮助，

Artur

编辑：以下是实施修复程序的完整代码：

public class App12 {

    Semaphore sem1 = new Semaphore(1);
    Semaphore sem2 = new Semaphore(0);
    Semaphore sem3 = new Semaphore(0);

    int count = 0;

    public void inc() throws InterruptedException {

        while (true) {

            if (Thread.currentThread().getId() == 10) {
                sem1.acquire();
                if (count != 50) {
                    count++;
                    System.out.println("Thread " + Thread.currentThread().getId() + " has incremented " + count);
                    sem2.release();
                } else {
                    sem2.release();
                    return;
                }
            }

            if (Thread.currentThread().getId() == 11) {
                sem2.acquire();
                if (count != 50) {
                    count++;
                    System.out.println("Thread " + Thread.currentThread().getId() + " has incremented " + count);
                    sem3.release();
                } else {
                    sem3.release();
                    return;
                }

            }

            if (Thread.currentThread().getId() == 12) {
                sem3.acquire();
                if (count != 50) {
                    count++;
                    System.out.println("Thread " + Thread.currentThread().getId() + " has incremented " + count);
                    sem1.release();
                } else {
                    sem1.release();
                    return;
                }
            }

        }
    }

    public static void main(String[] args) {

        App12 ap = new App12();
        for (int i = 0; i < 3; i++) {
            Thread th1 = new Thread(new Runnable() {
                public void run() {
                    try {
                        ap.inc();
                        // dec3();
                        System.out.println("Exist ");
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }

                }
            });
            th1.start();
        }
    }
}

注意：一旦计数为50，我将释放semathors，以便其他线程可以退出。

Answer 2

释放锁定以完成线程。

import java.util.concurrent.Semaphore;

public class App12 {

Semaphore sem1 = new Semaphore(1);
Semaphore sem2 = new Semaphore(0);
Semaphore sem3 = new Semaphore(0);


int count = 0;

public void inc() throws InterruptedException {

    while (true) {

        if (Thread.currentThread().getId() == 10) {
            sem1.acquire();
            if (count != 50) {
                count++;
                System.out.println("Thread" + Thread.currentThread().getId() + " has incremented " + count);

            } else {
                sem2.release();
                return;
            }
            sem2.release();

        }

        if (Thread.currentThread().getId() == 11) {
            sem2.acquire();
            if (count != 50) {
                count++;
                System.out.println("Thread" + Thread.currentThread().getId() + " has incremented " + count);

            } else {
                sem3.release();
                return;
            }
            sem3.release();
        }

        if (Thread.currentThread().getId() == 12) {
            sem3.acquire();
            if (count != 50) {
                count++;
                System.out.println("Thread" + Thread.currentThread().getId() + " has incremented " + count);

            } else {
                sem1.release();
                return;
            }
            sem1.release();

        }

    }

}

public static void main(String[] args) {

    App12 ap = new App12();

    for (int i = 0; i < 3; i++) {
        Thread th= new Thread(new Runnable() {
            public void run() {
                try {
                    ap.inc();
                    // dec3();

                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }

            }
        });
        th.start();
    }
}
}