Java/Android:同步 vs 队列实现 [英] Java/Android: Synchronized vs Queue implementation

问题描述

我可以问一个 Java 新手问题吗?

Can I ask a rookie Java question?

我正在从网上下载一些文件.此方法下载(网址位置)被多次调用.

I am downloading some files from the web. This method download(url location) is called multiple times.

public static void download(final String url) {
    Thread t = new Thread("download") {
        @Override
        public void run() {
            try {
                synchronized (object) {
                    // download & save
                }
            } catch(Exception e) {}
        }
    };
    t.start();
}

我添加了同步"，以便下载一个一个.(不能同时进行多次下载).
我猜即使多次调用 download()，synchronized 也会阻塞其他线程，直到第一个线程完成.

I added "synchronized" so that downloads happens one-by-one. (not multiple downloads occur at the same time).
I am guessing even though download() is called multiple times, synchronized will block other threads until the first thread is finished.

上面的代码能用吗?还是我必须实现队列?并一一出队?
同步可以阻止足够"的线程吗?(30?50?)还是有限制?

Will above code work? or do I have to implement Queue? and dequeue one-by-one?
Can synchronized block "enough" threads? (30? 50?) or does it have limits?

推荐答案

上面的代码能用吗?

是的，只要object在所有线程中都指向同一个对象，synchronized块中的代码一次只会被一个线程执行.

Yes, as long as object refers to the same object in all threads, the code in the synchronized block will only be executed by one thread at a time.

[...] 还是我必须实现队列?并一一出队?

一般来说，我建议您尽可能使用高级构造(例如来自 java.util.concurrent 包).例如，您可以考虑为这些类型的事情使用执行程序服务.

Generally speaking I would recommend you to use as high-level constructs as possible (for instance from the java.util.concurrent package). You may for instance consider using an executor service for these types of things.

[...] 同步可以阻塞足够多"的线程吗?(30?50?)还是有限制?

不，没有限制.至少不会接近 30 或 50 :-)

No, no limits. At least not near 30 or 50 :-)

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