How do I use NSConditionLock? Or NSCondition

EDIT: as @Bonshington commented, this answer refers to NSCondition (as opposed to NSConditionLock):

- (void) method1 {

    [myCondition lock];
    while (!someCheckIsTrue)
        [myCondition wait];


    // Do something.


    [myCondition unlock];
}

- (void) method2 {

    [myCondition lock];


    // Do something.


    someCheckIsTrue = YES;
    [myCondition signal];
    [myCondition unlock];
}

The someCheckIsTrue can be anything, it could be a simple BOOL variable or even something like [myArray count] == 0 && color == kColorRed, it doesn’t matter. It only matters that in one method you check for a condition while you have the lock and in another method you make changes that can make the condition become true also while having the lock. The magic is the wait and signal part: the wait actually unlocks the lock and reacquires it after some other thread called signal.