Worker thread in Android

Question

Hello im trying to simulate a worker thread in Android for testing. The activity has a button that calls notify() over the worker thread, and I want it go to sleep after 10 iterations of the bucle.

Thats my code and the stacktrace of the error. How can I solve it? Thanks

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);


    t= new Thread(){
        public void run(){
            int i=0;
            while(true){


                if (i%10==9){
                    //Simulated end of data until notified again
                    try {
                        this.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            Log.d("Test",""+i);
            SystemClock.sleep(1000);
            } 
        }
    };
    t.start();


    findViewById(R.id.button1).setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            t.notify();

        }
    });
}





08-06 05:39:45.320: ERROR/AndroidRuntime(4480): FATAL EXCEPTION: main
08-06 05:39:45.320: ERROR/AndroidRuntime(4480): java.lang.IllegalMonitorStateException: object not locked by thread before notify()
08-06 05:39:45.320: ERROR/AndroidRuntime(4480):     at java.lang.Object.notify(Native Method)
08-06 05:39:45.320: ERROR/AndroidRuntime(4480):     at com.example.memorycrash.MemoryCrashTestActivity$2.onClick(MemoryCrashTestActivity.java:51)
08-06 05:39:45.320: ERROR/AndroidRuntime(4480):     at android.view.View.performClick(View.java:2538)
08-06 05:39:45.320: ERROR/AndroidRuntime(4480):     at android.view.View$PerformClick.run(View.java:9152)
08-06 05:39:45.320: ERROR/AndroidRuntime(4480):     at android.os.Handler.handleCallback(Handler.java:587)
08-06 05:39:45.320: ERROR/AndroidRuntime(4480):     at android.os.Handler.dispatchMessage(Handler.java:92)
08-06 05:39:45.320: ERROR/AndroidRuntime(4480):     at android.os.Looper.loop(Looper.java:130)
08-06 05:39:45.320: ERROR/AndroidRuntime(4480):     at android.app.ActivityThread.main(ActivityThread.java:3687)
08-06 05:39:45.320: ERROR/AndroidRuntime(4480):     at java.lang.reflect.Method.invokeNative(Native Method)
08-06 05:39:45.320: ERROR/AndroidRuntime(4480):     at java.lang.reflect.Method.invoke(Method.java:507)
08-06 05:39:45.320: ERROR/AndroidRuntime(4480):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:842)
08-06 05:39:45.320: ERROR/AndroidRuntime(4480):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
08-06 05:39:45.320: ERROR/AndroidRuntime(4480):     at dalvik.system.NativeStart.main(Native Method)

Answer 1

So here is your solution. Answer was already there on StackOverflow.

In order to call wait(), notify(), or notifyAll() on an object you must first own the monitor of the object you wish to call the method on, so in you case within the runnable this would be how you would need to do it:

Runnable runnable = new Runnable() {
    public void run() {
      // wait(); This call wouldn't work
      syncronized (this) {
        wait();  // This call will work
      }
    }
};

To notify that runnable you would also have to have the monitor

// runnable.notifyAll(); this call will not work
syncronized (runnable) {
    runnable.notifyAll(); // this call will work
}