Crash due to removal of Elements like CCSprite from NSMutableArray

Question

So, here's how it goes.

I am currently working on Cocos2d game, which consists of many Obstacles. One obstacle gets added on the screen at an interval of 10 seconds like this.

ObstacleSprite* newObstacle = [ObstacleSprite spriteWithFile:@"Obstacle.png" rect:CGRectMake(0, 0, 20, 20)];
            newObstacle.position = ccp(mainPlayer1.position.x,10);
[self addChild:newObstacle];

[self.arrayForObstacles addObject:newObstacle];

Now, I insert these obstacles into the arrayForObstacles because I also want to keep checking whether the Obstacles and MainPlayer don't collide.

I check it with the help of this function.

- (void) checkCollisionWithObstacle
{
    if(mainPlayer1.playerActive)
    {
        for(int  i = 0; i < [self.arrayForObstacles count]; i++)
        {
            ObstacleSprite* newObstacle = [self.arrayForObstacles objectAtIndex:i];
            if(newObstacle != nil)
            {
                if(CGRectIntersectsRect([mainPlayer1 boundingBox], [newObstacle boundingBox]))
                {
                    mainPlayer1.livesLeft--;
                }
            }
        }
    }
}

THE ISSUE

Problem is when I get to certain score, one of the Obstacles gets deleted. Removal of Obstacles works as in First In-First Out (FIFO) mode. So, to delete obstacles, I write the following method :

- (void) keepUpdatingScore
{
    //update new score
    mainPlayer1.score+=10;
    //remove obstacle when score increases by 5k
    if(mainPlayer1.score > 5000 && mainPlayer1.score > 0)
    {        
        mainPlayer1.playerActive = NO;

        if([self.arrayForObstacles count] > 0)
        {            
            CCLOG(@"count is %d",[self.arrayForObstacles count]);
            ObstacleSprite* newObstacle = [self.arrayForObstacles objectAtIndex:0];
            [self.arrayForObstacles removeObjectAtIndex:0];
            [self removeChild:newObstacle cleanup:YES];

            CCLOG(@"count is %d",[self.arrayForObstacles count]);
        }

        mainPlayer1.playerActive = YES;

    }    
    else
    {

    }

It crashes when score crosses 5000 mark!

UPDATE

Crash happens when it again goes to the method checkCollisionWithObstacle.

This is the THREAD Look.

THis is the line Which crashes.

Answer 1

you seem to be using mainPlayer1.playerActive as a semaphore to block checking the checkCollisionWithObstacle loop from a delete in the keepUpdatingScore method (are they asynchronous ?). Assuming they are, the way you are blocking the loop access wont work if the code enters keepUpdatingScore AFTER the loop started in checkCollisionWithObstacle ... your mileage will vary.