Question

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GCD : How to write and read to variable from two threads

I am developing a iOS app in which i am using sqlite database.I have to perform multithreading but on sqlite database I am able to do only one thing at a time.So I need to implement concept of semaphore .So plz help me

Answer 1

You can use the @synchronized directive as a mutex. If you have all your methods for manipulating the sqlite database in a single data manager created using a singleton and shared throughout the project you can use that object as the lock token, e.g.:

- (void)myMethod:(id)globalDataManager {
    @synchronized(globalDataManager) {
        // Everything between the braces is protected by the @synchronized directive.
    }
}

And from within the data manager you can use @synchronized(self) for the same protection.

You will only need a mutex for this so don’t worry about extra code for implementing semaphores.