Thread 在服务中启动线程创建

Question

我想在服务中创建一个带有 3 个线程的固定池的执行器。

这 3 个线程将根据我的 SQLite 数据库中的数据做一些工作。

有没有办法告诉线程"call"服务上的一些方法会告诉他，"a thread is done, you can now pull the data from the DB and start a new thread"

这样我就可以操作数据库，下一个线程将相应地进行操作。

我所要做的就是用我数据库中的所有数据填充队列，这样它就不会对数据库中的更改做出反应，因为我已经提取了所有数据

编辑：一些代码可以更好地理解

public class MediaDownloadService extends Service {
    public int onStartCommand(Intent intent, int flags, int startId) {
    executor = new ThreadPoolExecutor(2,3,3000,TimeUnit.MILLISECONDS,new LinkedBlockingQueue<Runnable>());
    //initiale start of new threads (first run)
}

public void startNewThread(){
    if(helper.requestsExists()){
        Map<Integer,String> requestMap = helper.getRequestsToExcute(0);
        Set<Integer> keySet = requestMap.keySet();
        Iterator<Integer> iterator = keySet.iterator();
        executor.submit(new MyThread(file, getApplicationContext(), iteratorNext), 1);
    }else{
        executor.shutdown();
        this.stopSelf();
    }
}

和线程本身：

public class MyThread implements Runnable {

private File _file;
private Context context;
private DBHelper helper;
private int requestId;

public MyThread(File file, Context context, int requestId) {
    this._file = file;
    this.context = context;
    this.requestId = requestId;
}

@Override
public void run() {
        // Thread work here

        helper.deleteRequest(requestId);// remove from db to prevent infinite loop

        // THIS IS THE QUESTION
        MediaDownloadService.startNewThread();// ??? can it be done

    } catch (IOException e) {
        Log.e("Callable try", post.toString());

    }
}

我当然不希望它是静态的，还有其他方法吗？

Answer 1

我认为您在这里有一些误解：Executor.submit() 不接受 Thread，而是接受 Runnable。它会将 Runnable 放入队列中，并可能（在一段时间后）分配一个线程来执行该可运行对象指定的操作。整个执行器的存在，让你不必自己做线程的创建、管理和任务调度。

ThreadPoolExecutor 因此已经实现了您正在尝试实现的排队功能。因此，一种解决方案是在所有任务进入时将所有任务简单地提交给执行器。执行器将它们排队并将它们调度到可用线程。

还要注意 AsyncTask.execureOnExecutor() 这也让你有可能在主线程上有 onPostExecute() 运行。

请将 MyThread 和 startNewThread() 重命名为其他名称。前者不是线程，只是任务，后者只是向执行者提交工作。

Answer 2

经过一番研究，我设法找到了解决方案：

首先我通过这里学习了如何使用IBinder绑定服务： https://www.youtube.com/watch?v=0c4jRCm353c

所以我的服务现在看起来像这样：

public class MediaDownloadService extends Service {

private DBHelper helper;
private ExecutorService executor;
private final IBinder sharonsBinder = new MyLocalBinder();
File file;

@Override
public IBinder onBind(Intent intent) {
    return sharonsBinder;
}


@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    helper = new DBHelper(getApplicationContext());
    executor = new ThreadPoolExecutor(2,3,3000,TimeUnit.MILLISECONDS,new LinkedBlockingQueue<Runnable>());
    Log.e("requestsExists", helper.requestsExists() + "");
   if(helper.requestsExists()){
        // map of the index of the request and the string of the absolute path of the request
        Map<Integer,String> requestMap = helper.getRequestsToExcute(3);
        Set<Integer> keySet = requestMap.keySet();
        Iterator<Integer> iterator = keySet.iterator();
        Log.e("MAP",requestMap.toString());
        //checks if the DB requests exists
        if(!requestMap.isEmpty()){
            //execute them and delete the DB entry
            while(iterator.hasNext()){
                int iteratorNext = iterator.next();
                Log.e("ITREATOR", iteratorNext + "");
                file = new File(requestMap.get(iteratorNext));
                Log.e("file", file.toString());
                Log.e("thread Opened", "Thread"+iteratorNext);
                executor.submit(new MyTask(file, getApplicationContext(), iteratorNext), 1);
                helper.requestTaken(iteratorNext);
            }
        }
    }
    return START_STICKY;
}

public void startNewTask(){
    if(helper.requestsExists()){
        Map<Integer,String> requestMap = helper.getRequestsToExcute(1);
        Set<Integer> keySet = requestMap.keySet();
        Iterator<Integer> iterator = keySet.iterator();
        while(iterator.hasNext()){
                int iteratorNext = iterator.next();
                file = new File(requestMap.get(iteratorNext));
                Log.e("file", file.toString());
                Log.e("thread Opened", "Thread"+iteratorNext);
                executor.submit(new MyTask(file, getApplicationContext(), iteratorNext), 1);
                helper.requestTaken(iteratorNext);
            }
    }else{
        executor.shutdown();
        this.stopSelf();
    }
}
 public class MyLocalBinder extends Binder{
    MediaDownloadService getService(){
        return MediaDownloadService.this;
    }
}

现在我将我的任务绑定到服务，这样它就可以像这样调用 startNewTask() 方法：

public class MyTask implements Runnable {

private File _file;
private Context context;
private DBHelper helper;
private int requestId;
private MediaDownloadService sharonsService;
boolean isBound = false;

public MyTask(File file, Context context, int requestId) {
    this._file = file;
    this.context = context;
    this.requestId = requestId;

}

@Override
public void run() {
    Intent intent = new Intent(context,MediaDownloadService.class);
    context.bindService(intent,sharonsConnection,Context.BIND_AUTO_CREATE);

        // some work here
        sharonsService.startNewTask();

    } catch (IOException e) {
        Log.e("Callable try", post.toString());

    }
}

private ServiceConnection sharonsConnection = new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName componentName, IBinder service) {
       MyLocalBinder binder = (MyLocalBinder) service;
        sharonsService = binder.getService();
        isBound = true;
    }

    @Override
    public void onServiceDisconnected(ComponentName componentName) {
        isBound = false;
    }
};

工作正常，只有在任务完成时才打开线程

希望对遇到同样问题的人有所帮助。

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