Suspend consumer in producer/consumer pattern

Question

I have producer and consumer connected with BlockingQueue.

Consumer wait records from queue and process it:

Record r = mQueue.take();
process(r);

I need pause this process for a while from other thread. How to implement it?

Now I think implement it such, but it's looks like bad solution:

private Object mLock = new Object();
private boolean mLocked = false;

public void lock() {
    mLocked = true;
}

public void unlock() {
    mLocked = false;
    mLock.notify();

}

public void run() {
    ....
            Record r = mQueue.take();
            if (mLocked) {
                mLock.wait();
            }
            process(r);
}

Answer 1

I think your solution is simple and elegant, and think you should keep it with some modifications. The modifications I propose are synchronization.

Without it, thread interference and memory consistancy errors can (and very often does) occur. On top of that, you can't wait or notify on a lock you don't own (and you own it if you have it inside a synchronized block..). The fix is easy, just add a mLock synchronize block where you wait/notify on it. Also, as you're changing mLocked from a different thread you will want to mark it volatile.

private Object mLock = new Object();
private volatile boolean mLocked = false;

public void lock() {
    mLocked = true;
}

public void unlock() {
    synchronized(mlock) {
        mLocked = false;
        mLock.notify();
    }

}

public void run() {
    ....
            Record r = mQueue.take();
            synchronized(mLock) {
                while (mLocked) {
                    mLock.wait();
                }
            }
            process(r);
}