0

请不要将以下问题视为重复问题..!

我开发了一个类,它可以让多线程按顺序运行,一次一个,按顺序运行。该类的claimAccess函数和releaseAccess函数之间的所有应用程序代码一次只能在一个线程中执行。所有其他线程将在队列中等待,直到前一个线程完成。现在请告知是否可以通过执行器、循环障碍或倒计时闩锁等其他方式来实现同样的事情..!!请建议如何通过其他方法来构建

import java.util.ArrayList;
import java.util.List;

public class AccessGate {
    protected boolean shouldWait = false;
    protected final List waitThreadQueue = new ArrayList();

    /**
     * For a thread to determine if it should wait. It it is, the thread will
     * wait until notified.
     * 
     */
    public void claimAccess() {
        final Thread thread = getWaitThread();
        if (thread != null) {
            // let the thread wait untill notified
            synchronized (thread) {
                try {
                    thread.wait();
                } catch (InterruptedException exp) {
                }
            }
        }
    }

    /**
     * For a thread to determine if it should wait. It it is, the thread will be
     * put into the waitThreadQueue to wait.
     * 
     */
    private synchronized Thread getWaitThread() {
        Thread thread = null;
        if (shouldWait || !waitThreadQueue.isEmpty()) {
            thread = Thread.currentThread();
            waitThreadQueue.add(thread);
        }
        shouldWait = true;
        return thread;
    }

    /**
     * Release the thread in the first position of the waitThreadQueue.
     * 
     */
    public synchronized void releaseAccess() {
        if (waitThreadQueue.isEmpty()) {
            shouldWait = false;
        } else {
            shouldWait = true;
            // give the claimAccess function a little time to complete
            try {
                Thread.sleep(10);
            } catch (InterruptedException exp) {
            }

            // release the waiting thread
            final Thread thread = (Thread) waitThreadQueue.remove(0);
            synchronized (thread) {
                thread.notifyAll();
            }
        }
    }
}
4

2 回答 2

2

是的,有更简单的方法可以做到这一点。最简单的就是使用监视器,无需等待、睡眠或任何其他恶作剧:

// somewhere visible
public final Object accessGate = new Object();

// in your application code
synchronized (accessGate) {
    // this block will be executed only in one thread at one time
}

Java 的内置监视器几乎提供了您需要的语义。唯一的问题是不能保证线程持有锁的顺序。这取决于底层操作系统如何处理锁(信号量或互斥锁或其他)的排序。操作系统可以很好地保证您需要的行为,但这通常不是可移植的。

如果您需要便携的订购保证,您有几个选择。最明显的是将ReentrantLock公平设置为 true:

// somewhere visible
public final Lock accessGate = new ReentrantLock(true);

// in your application code
accessGate.lock();
try {
    // this block will be executed only in one thread at one time
}
finally {
    accessGate.unlock();
}

另一个是Semaphore一个单一的许可和公平设置为真:

// somewhere visible
public final Semaphore accessGate = new Semaphore(1, true);

// in your application code
accessGate.acquire();
try {
    // this block will be executed only in one thread at one time
}
finally {
    accessGate.release();
}

这两个有非常相似的行为。

于 2012-12-09T09:52:28.030 回答
2

这是通过ExecutorService

Executors.singleThreadExecutor()将一次执行一个任务,并按顺序执行。

创建一个Executor使用单个工作线程在无界队列上操作的线程。(但请注意,如果该单线程在关闭前的执行过程中因失败而终止,如果需要执行后续任务,则新的线程将取代它。)任务 保证按顺序执行,并且不会有超过一个任务处于活动状态在任何给定时间。

于 2012-12-09T09:05:10.857 回答