CATransaction lock example in Objective C (iOS).

CATransaction lock

Attempts to acquire a recursive spin-lock lock, ensuring that returned layer values are valid until unlocked.

+ (void)lock

Discussion of [CATransaction lock]
Core Animation uses a data model that promises not to corrupt the internal data structures when called from multiple threads concurrently, but not that data returned is still valid if the property was valid on another thread. By locking during a transaction you can ensure data that is read, modified, and set is correctly managed.

CATransaction lock example.

- (void) updateUI
{
[CATransaction lock];
[CATransaction setValue:(id)kCFBooleanTrue
                 forKey:kCATransactionDisableActions];
[CATransaction begin];
myLayer.path = [UIBezierPath bezierPathWithOvalInRect:theRect].CGPath;
myLayer.bounds = theBounds;
[CATransaction commit];

[CATransaction flush];
[CATransaction setValue:(id)kCFBooleanFalse
                 forKey:kCATransactionDisableActions];
[CATransaction unlock];
}

Example of [CATransaction lock].

In your touch handling method, wrap the animations in a transaction and lock:

[CATransaction lock];
[CATransaction begin];

// update the sublayers with new animations

[CATransaction commit];
[CATransaction unlock];

CATransaction lock example.

CGPathRef newPath = CGPathCreateWithRect(aLayer.frame, nil);
[CATransaction lock];
[CATransaction begin];
[CATransaction setAnimationDuration:5.0f];
CABasicAnimation *ba = [CABasicAnimation animationWithKeyPath:@"path"];
ba.autoreverses = YES;
ba.fillMode = kCAFillModeForwards;
ba.repeatCount = HUGE_VALF;
ba.fromValue = (id)aLayer.path;
ba.toValue = (__bridge id)newPath;
[aLayer addAnimation:ba forKey:@"animatePath"];
[CATransaction commit];
[CATransaction unlock];

End of CATransaction lock example article.