Here's how to do a mutex when writing a multithreaded Cocoa app. Use the NSLock class...

// In your class' header. (ClassName.h)
@interface ClassName: NSObject
{
    NSLock*     mutex;
}

// In your class' source. (ClassName.m)
@implementation ClassName

- (id)init
{
    if ( (self = [super init] ) ) 
    {
        mutex = [[NSLock alloc] init];
        
        // Other initialization stuff here..
    }
    return self;
}

- (void)dealloc
{
    if ( mutex )
    {
        [mutex release];
        mutex = NULL;
    }

    // Other cleanup code here...
	
    [super dealloc];
}


- (void)someFunction
{
    [mutex lock];

    // Do some stuff.

    [mutex unlock];
}