Android Service and worker thread ReentrantLock infinite loop

Question

Hi I want to get rid of an infinite loop which holds a worker thread in a service.

I try to use the ReentrantLock() methods but I can't seem to get it to work.

My worker thread calls from JNI the nativeWaitForTask method and goes to sleep.

But my service main thread can't seem to wake him up in the submitTask method where he should signal the worker thread.

It's like the await() call blocked the service's main thread aswell.

But they are on different threads as far as I know...

What did I do wrong? Why doesn't it work?

    private synchronized void nativeWaitForTask() {

    threadLock.lock();

    try {


        while(opcode == SR_Manager.STATE_IDLE) {

            newTask.await();
        }

    }catch (InterruptedException e) {

        e.printStackTrace();
        Log.e(SR_Manager.DEBUG_TAG,"Failed to wait for new task! " + e.toString());

    }finally {

        threadLock.unlock();
    }
}


    private synchronized void submitTask() {

    if (nativeMain.isAlive()) {

        dstImageName = sr.getDstImageName();

        if (sr.getSrcImagePath() != null && !sr.getSrcImagePath().equals(srcImagePath)) {

            srcImagePath = sr.getSrcImagePath();
            width = sr.getWidth();
            height = sr.getHeight();
            format = sr.getFormat();
            algorithm = sr.getAlgorithm();
            value = sr.getValue();
            saveOutput = sr.getSaveOutput();
            opcode = SR_Manager.STATE_LOAD_IMAGE;

        } else if (sr.getOpcode() != SR_Manager.STATE_LOAD_IMAGE) {

            algorithm = sr.getAlgorithm();
            value = sr.getValue();
            saveOutput = sr.getSaveOutput();
            opcode = sr.getOpcode();
        }

        t0 = System.currentTimeMillis();

    } else {

        // No native thread no service...
        silentCrash(-100);
    }

    // Wake the worker thread which waits for the new task condition
    threadLock.lock();
    newTask.signal();
    threadLock.unlock();
}

score 0 · Answer 1 · answered Sep 22 '16 at 08:10

The error was using the synchronized keyword for the methods. It gave a double lock to the worker thread one with the lock object and one with the service instance (this) object and blocked the service's main thread.

This works nicely now and dropped CPU usage from a constant 12% for the infinite loop to 0% while the worker thread waits for tasks.

Android Service and worker thread ReentrantLock infinite loop

1 Answers1