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如何在AsyncTask doInBackground()中使用同步对象?

thread-safety android-asynctask multithreading android java

2

Truong Giang Dam · 技术社区 · 8 年前

我在后台线程中使用同步对象时遇到了问题。我已经在示例nutshell中指定了问题:

我编写的简单类如下:

public class UIThreadClass {

   MyObject object;

   UIThreadClass() {
      object = new MyObject();

      object.doActionOne();
      object.doActionTwo();
  }
}

现在,我的任务是通过将两种方法放置到非UI线程来改进代码。我正在使用AsyncTask

对于doActionOne()

private static class DoActionOneTask extends AsyncTask<Void, Void, Void> {

    private WeakReference<MyObject> wObject;

    DoActionOneTask(MyObject object) {
        wObject = new WeakReference<>(object);
    }

    @Override
    protected Void doInBackground(Void... voids) {
       if(wObject.get() != null) {
          MyObject myObject = wObject.get();
          myObject.doActionOne();
       }

       return null;
    }
}

对于doActionTwo()

private static class DoActionTwoTask extends AsyncTask<Void, Void, Void> {

    private WeakReference<MyObject> wObject;

    DoActionOneTask(MyObject object) {
        wObject = new WeakReference<>(object);
    }

    @Override
    protected Void doInBackground(Void... voids) {
       if(wObject.get() != null) {
          MyObject myObject = wObject.get();
          myObject.doActionTwo();
       }

       return null;
    }
}

现在在UI线程中调用它们

public class UIThreadClass {

   MyObject object;

   UIThreadClass() {
      object = new MyObject();

      new DoActionOneTask(object).execute();
      new DoActionTwoTask(object).execute();
  }
}

问题是:

使用AsyncTask时-如何同步对象以确保 doActionTwo()总是在doActionOne()方法之后调用?。

我试过使用 同步(myObject){myObject.doActionOne();} 在doInBackground()中,但系统警告我,myObject只是局部变量,很难保证正确性。

有人能帮我解决这个问题吗?非常感谢!

1 回复 | 直到 8 年前

1

2

Raj Suvariya 8 年前

你不需要做任何事。它们将按照Android文档顺序执行

Order of execution
When first introduced, AsyncTasks were executed serially on a single background thread. Starting with DONUT, this was changed to a pool of threads allowing multiple tasks to operate in parallel. 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.