如何限制Java中的最大线程数? [英] How to limit maximum number of threads in Java?

问题描述

我用Java SE编写了一个简单的Web服务器，没有使用任何API.它具有GUI，您可以在其中启动/停止服务器并查看其使用了多少线程.

I programmed a simple webserver in Java SE, without using any API. It has a GUI where you can start/stop server and see how many threads it uses.

老师的要求之一是它必须支持多线程，并且您可以在启动服务器之前控制最大线程.

One of requests from our teacher is that it must support multithreading, and you can control maximum threads before starting the server.

我有扩展Thread的WebServer类，它作为一个线程运行.它具有字段MAX_THREADS和一个thread_counter.

I have WebServer class that extends Thread and it runs as one thread. It has fields MAX_THREADS and a thread_counter.

WebServer:

WebServer:

public static final int MAX_THREADS = 5;
public static int threads_counter = 0;

public void run() {
    while (isRunning) {
        try {
            Socket socket = _serverSocket.accept();

            if (threads_counter >= MAX_THREADS) {
                Thread.sleep(100);
                System.out.println("OVERLOAD");
            } else {
                new Handler(socket, new File(rootDir)).start();
            }
        } catch (IOException ex) {
            Logger.getLogger(WebServer.class.getName()).log(Level.SEVERE, null, ex);
        } catch (InterruptedException ex) {
            Logger.getLogger(WebServer.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}

有Handler类，它也扩展了Thread.我想将Handler的数量限制为MAX_THREADS.

There is Handler class which also extends Thread. I want to limit the number of Handlers to MAX_THREADS.

以下是Handler的外观:

Here is how Handler looks:

public void run() {
    synchronized (WebServer.class) {
        WebServer.threads_counter++;
    }
    this.setName("thread no. " +WebServer.threads_counter);
    System.out.println(this.getName());
    HandleRequest(_socket);
    synchronized (WebServer.class) {
        WebServer.threads_counter--;
    }
}

但是，这并不总是能正常工作.有时，它的开始时间超过MAX_THREADS个Handler，我不知道如何解决.

This does not always work as expected, however. Sometimes, it starts more than MAX_THREADS Handlers and I don't know how to solve it.

您能帮我解决我的情况吗?

Could you please help me with my situation?

推荐答案

我建议使用

I would suggest to use ExecutorService instead of creating threads by hand, more specifically Executors.newFixedThreadPool.

这样，您就可以更好地控制执行.

That way, you have more control over execution.

另一方面，在当前代码中，用

On other hand, in your current code, replace synchronized block and incrementing of static variable with AtomicInteger.

在业余时间，请查看

In spare time, take a look at java.util.concurrent package, it contains lots of great stuff usable for multithreading.

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