create and use semaphore in swift

In Swift, we can create and use Semaphore using the DispatchSemaphore class provided by the Dispatch framework.

Here's an example implementation:

main.swift
import Foundation

// Create a Semaphore object that will allow only 5 queued tasks to execute
let semaphore = DispatchSemaphore(value: 5)

for i in 1...10 {
    // Wait for the semaphore to allow us to proceed
    semaphore.wait()

    DispatchQueue.global().async {
        // Perform some asynchronous task

        // Signal the semaphore that a task has completed
        semaphore.signal()
    }
}
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In the example above, we create a Semaphore object semaphore with an initial value of 5, which means that only 5 tasks can be queued up and run concurrently. We then loop 10 times and asynchronously perform some task in each iteration. Before each task is executed, we call semaphore.wait() which will decrement the value of the semaphore by 1, and wait if the value is 0, until another task signals it. Once a task has completed, we call semaphore.signal() to increment the value of the semaphore by 1, which will allow another queued task to proceed.

This is a simple implementation of Semaphore in Swift to achieve concurrency control where there's a need to limit concurrency.