android - AsyncTask 不会与第二个 AsyncTask 同时运行

Question

我有一个异步任务

private class LoadData extends AsyncTask<String, Void, String> {
    private String WEBURL;
    LoadData(String url){
        this.WEBURL=url;
    }
    protected String doInBackground(String... params) {
        System.out.println("Downloading");
        URL url = new URL(WEBURL);
        URLConnection conn = url.openConnection();
        conn.connect();
        byte buffer[] = new byte[1024];
        InputStream in = new BufferedInputStream(url.openStream());
        String contents="";
        while((count = in.read(buffer))!=-1){
        total+=count;
        contents += new String(buffer, 0, count);
        }
        System.out.println("Downloaded");
        in.close;
    }
}

如果我尝试通过调用生成两个 LoadData

new LoadData("http://www.google.com").execute();
new LoadData("http://www.stackoverflow.com").execute();

我期望输出:

Downloading Downloading Downloaded Downloaded

但是我得到了

Downloading Downloaded Downloading Downloaded

这意味着 AsyncTask 不会同时执行。为什么是这样？我认为线程的意义在于不会发生这种情况？ + 有没有办法让它们同时运行而无需更改太多代码？

Answer 1

根据 AsyncTask documentation在执行顺序下:

Starting with HONEYCOMB, tasks are executed on a single thread to avoid common application errors caused by parallel execution. If you truly want parallel execution, you can invoke executeOnExecutor(java.util.concurrent.Executor, Object[]) with THREAD_POOL_EXECUTOR.

即，new LoadData("http://www.google.com").executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);