Question

My function has to return data just after my thread end, I am using the wait() method after start() my thread but it doesn’t work :

private class getDataThread extends Thread {
    @Override
    public void run() {
        super.run();
        while (true) {
            try {
                // ...
                Thread.sleep(100);
            } catch (InterruptedException e) {
                // ...
            }
        }
    }
}

public void getSensorValues(Bundle bundle) {
    // ...
    getDataThread gdt = new getDataThread();
    gdt.start();
    try {
        gdt.wait();
    } catch (InterruptedException e) {
        // ...
    }
}

in LogCat :

: An exception occurred during execution !
: Exception caught: java.lang.reflect.InvocationTargetException
: Exception cause: (SYSTEM) java.lang.IllegalMonitorStateException: object not locked by thread before wait() in getSensorValues
: status::FAILURE - output:: Possible errors: (SYSTEM) java.lang.IllegalMonitorStateException: object not locked by thread before wait() in getSensorValues.

What I’m doing wrong?

Answer 1

You’re looking for join, not wait:

public void getSensorValues(Bundle bundle) {
    // ...
    getDataThread gdt = new getDataThread();
    gdt.start();
    try {
        gdt.join();
    } catch (InterruptedException e) {
        // ...
    }
}

wait has a different purpose, which is to signal another thread that an event has occurred. It requires a matching call to notify. Furthermore, you need to acquire the lock on the object which is being used to wait/notify, which is why you are getting that exception.

And another thing: starting a thread and then immediately joining it is redundant. You might as well execute everything on the main thread.