How can the Semaphore mechanism be integrated into an existing program to manage resource access?

Semaphore is used to limit the number of threads that can access a certain resource simultaneously.

To integrate a semaphore into an existing iOS program (for example, in Swift), you need to:

1. Create an instance of DispatchSemaphore with a maximum number of permits (for example, 1 for a mutex).
2. Before accessing the resource, call wait() — if permits are exhausted, the thread will wait.
3. After finishing with the resource, call signal() to release the permit.

Example:

let semaphore = DispatchSemaphore(value: 2) // maximum 2 concurrent accesses

func accessResource() {
    semaphore.wait() // wait for permit
    defer { semaphore.signal() } // ensure release

    // Work with the resource
    print("Accessing resource")
    Thread.sleep(forTimeInterval: 1) // simulate work
}

// Called from multiple threads
DispatchQueue.global().async { accessResource() }
DispatchQueue.global().async { accessResource() }
DispatchQueue.global().async { accessResource() }

This way, you can control concurrent access and avoid race conditions or resource overloads.