如何在Java中进行线程限制 [英] How to make a thread limit in Java

问题描述

假设我要读取1000个文件，由于某些限制，我想最多并行读取5个文件.而且，一旦其中一个完成，我希望一个新的开始.

Let's say I have 1000 files to read and because of some limits, I want to read maximum 5 files in parallel. And, as soon as one of them is finished, I want a new one starts.

我有一个具有文件列表的主要功能，每当一个线程完成时，我尝试更改一个计数器.但这不起作用！

I have a main function who have the list of the files and I try changing a counter whenever one thread is finished. but it doesn't works!

有什么建议吗?

以下是主要功能循环

for (final File filename : folder.listFiles()) {

    Object lock1 = new Object();
    new myThread(filename, lock1).start();
    counter++;
    while (counter > 5);
}

推荐答案

这样的散布线程是不可行的.使用ExecutorService并将池指定为5.将所有文件放入BlockingQueue或另一个线程安全的集合中，所有正在执行的文件都可以随意poll().

Spawning threads like this is not the way to go. Use an ExecutorService and specify the pool to be 5. Put all the files in something like a BlockingQueue or another thread-safe collection and all the executing ones can just poll() it at will.

public class ThreadReader {

    public static void main(String[] args) {
        File f = null;//folder
        final BlockingQueue<File> queue = new ArrayBlockingQueue<File>(1000);
        for(File kid : f.listFiles()){
            queue.add(kid);
        }

        ExecutorService pool = Executors.newFixedThreadPool(5);

        for(int i = 1; i <= 5; i++){
            Runnable r = new Runnable(){
                public void run() {
                    File workFile = null;
                    while((workFile = queue.poll()) != null){
                        //work on the file.
                    }
                }
            };
            pool.execute(r);
        }
    }
}

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