iOS HELP ! NSCondition problem

[mars.tsang]

I have some code like below :

// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
    [super viewDidLoad];
	//
	_myCondition = nil;
	//

	//
	NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:30 
													 target:self
												   selector:@selector(threadTester)
												   userInfo:nil
													repeats:YES];
	[timer fire];
	
}


- (void)threadTester{
	//NSAutoreleasePool *pool =  [[NSAutoreleasePool alloc] init];
	if(_myCondition){
		[_myCondition release];
		_myCondition = [[NSCondition alloc] init];
	}
	[_myCondition lock];
	_threadCount = -2;
	[_myCondition unlock];
	//
	NSLog(@"");
	NSLog(@"------------------------------------------------------------------------------");
	[NSThread detachNewThreadSelector:@selector(threadOne) toTarget:self withObject:nil];
	[NSThread detachNewThreadSelector:@selector(threadTwo) toTarget:self withObject:nil];
	[NSThread detachNewThreadSelector:@selector(threadThree) toTarget:self withObject:nil];
	//
	//[pool release];
	return;
}

- (void)threadOne{
	NSLog(@"@@@ In thread one start.");
	[_myCondition lock];
	
	int n = rand()%5 + 1;
	NSLog(@"@@@ Thread one Will sleep %d seconds ,now _threadCount is : %d",n,_threadCount);
	sleep(n);
	_threadCount ++ ;
	NSLog(@"@@@ Thread one has sleep %d seconds ,now _threadCount is : %d",n,_threadCount);
	[_myCondition signal];
	NSLog(@"@@@ Thread one has signaled ,now _threadCount is : %d",_threadCount);
	[_myCondition unlock];
	NSLog(@"@@@ In thread one complete.");
	[NSThread exit];
	//_threadCount ++ ;
	return;
}

- (void)threadTwo{
	NSLog(@"### In thread two start.");
	[_myCondition lock];
	
	int n = rand()%5 + 1;
	NSLog(@"### Thread two Will sleep %d seconds ,now _threadCount is : %d",n,_threadCount);
	sleep(n);
	_threadCount ++ ;
	NSLog(@"### Thread two has sleep %d seconds ,now _threadCount is : %d",n,_threadCount);
	[_myCondition signal];
	NSLog(@"### Thread two has signaled ,now _threadCount is : %d",_threadCount);
	[_myCondition unlock];
	NSLog(@"### In thread two complete.");
	[NSThread exit];
	return;
}

- (void)threadThree{
	NSLog(@"<<< In thread three start.");
	[_myCondition lock];
	while (_threadCount < 0) {
		[_myCondition wait];
	}
	NSLog(@"<<< In thread three ,_myCondition now is %d ,will start work.",_myCondition);
	[_myCondition unlock];
	NSLog(@"<<< In thread three complete.");
	[NSThread exit];
	return;
}

so according to the code ,threadThree is supposed to run after both threadOne and threadTwo finished .
But the log told me that some time threadThree began to execute after _threadCount ++ and before the [myCondition signal] in either threadOne or threadTwo ,when _theadCount became 0 . Is it that threadThree will notice the _threadCount value changed when [myCondition signal] called ??

Hope someone can help me out .

I also post the project code to give more info.

Thanks a lot!

 

[mars.tsang]

OK，I found a bug in my code ,
if(_myCondition){
[_myCondition release];
_myCondition = [[NSCondition alloc] init];
}

it shoul be

if(_myCondition){
[_myCondition release];
_myCondition = [[NSCondition alloc] init];
}else{
_myCondition = [[NSCondition alloc] init];
}


after the change ,the code works ok !