Been struggling with this for over 2 days now.
implemented the answer I saw on here Specify task order execution in Java
public class PriorityExecutor extends ThreadPoolExecutor {
public PriorityExecutor(int corePoolSize, int maximumPoolSize,
long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
}
//Utitlity method to create thread pool easily
public static ExecutorService newFixedThreadPool(int nThreads) {
return new PriorityExecutor(nThreads, nThreads, 0L,
TimeUnit.MILLISECONDS, new PriorityBlockingQueue<Runnable>());
}
//Submit with New comparable task
public Future<?> submit(Runnable task, int priority) {
return super.submit(new ComparableFutureTask(task, null, priority));
}
//execute with New comparable task
public void execute(Runnable command, int priority) {
super.execute(new ComparableFutureTask(command, null, priority));
}
}
public class ComparableFutureTask<T> extends FutureTask<T>
implements
Comparable<ComparableFutureTask<T>> {
volatile int priority = 0;
public ComparableFutureTask(Runnable runnable, T result, int priority) {
super(runnable, result);
this.priority = priority;
}
public ComparableFutureTask(Callable<T> callable, int priority) {
super(callable);
this.priority = priority;
}
@Override
public int compareTo(ComparableFutureTask<T> o) {
return Integer.valueOf(priority).compareTo(o.priority);
}
}
The Runnable I use: MyTask
public class MyTask implements Runnable{
public MyTask(File file, Context context, int requestId) {
this._file = file;
this.context = context;
this.requestId = requestId;
}
@Override
public void run() {
// some work
} catch (IOException e) {
Log.e("Callable try", post.toString());
}
}
My service: MediaDownloadService
public class MediaDownloadService extends Service {
private DBHelper helper;
Notification notification;
HashMap<Integer,Future> futureTasks = new HashMap<Integer, Future>();
final int _notificationId=1;
File file;
@Override
public IBinder onBind(Intent intent) {
return sharonsBinder;
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
helper = new DBHelper(getApplicationContext());
PriorityExecutor executor = (PriorityExecutor) PriorityExecutor.newFixedThreadPool(3);
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(0);
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);
Future future = executor.submit(new MyTask(file, this, iteratorNext),10);
futureTasks.put(iteratorNext, future);
helper.requestTaken(iteratorNext);
}
Log.e("The priority queue",executor.getQueue().toString());
}else{
Log.e("stopself", "stop self after this");
this.stopSelf();
}
}
return START_STICKY;
}
keep getting an error on this line : Future future = executor.submit(new MyTask(file, this, iteratorNext),10);
Even tho an executor.submit(); suppose to return a future object i keep getting
Caused by: java.lang.ClassCastException: java.util.concurrent.FutureTask cannot be cast to java.lang.Comparable
at java.util.concurrent.PriorityBlockingQueue.siftUpComparable(PriorityBlockingQueue.java:318)
at java.util.concurrent.PriorityBlockingQueue.offer(PriorityBlockingQueue.java:450)
at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1331)
at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:81)
at com.vit.infibond.test.PriorityExecutor.submit(PriorityExecutor.java:26)
at com.vit.infibond.test.MediaDownloadService.onStartCommand(MediaDownloadService.java:65)
Can anyone save me from this nightmare?
I tried doing as this answer suggest as well Testing PriorityBlockingQueue in ThreadPoolExecutor
by adding the forNewTask override only to get casting execption again but this time for RunnableFuture.
I understand something basic is missing on my understanding and would appreciate a depth explanation...
By looking at the source code for java.util.concurrent.ThreadPoolExecutor it seems to be a real pain to get this working when submitting futures. You have to override protected methods that feels internal and do some nasty casts.
I suggest you simply use the execute method instead. There is no wrapping of the Runnable going on there so it should work.
If you need to wait for the results of your jobs I suggest implementing that on your own to avoid having to mess around with the ThreadPoolExecutor internals.