BalkingPattern.md

Balking Pattern

Introduction

Concurrency is a crucial aspect of software design, as it allows for the efficient execution of multiple tasks simultaneously. When dealing with concurrent programming, it is essential to handle situations where an object's method is called when it's not ready to perform the requested action. The Balking design pattern provides an elegant solution for such cases by refusing to execute the method when the object is in an undesirable state.

In this article, we will discuss the Balking design pattern in Swift, its benefits, and how to implement it in your applications.

The Balking Pattern

The Balking pattern is a concurrency design pattern used to handle situations where an object's method is called when the object is not ready to perform the requested action. In such cases, the method "balks" or refuses to execute, often returning immediately without doing anything. This pattern is commonly used to avoid blocking when an object is in an undesirable state for a certain operation.

Here's an example of the Balking pattern implemented in Swift:

import Foundation

class WashingMachine {
    enum State {
        case idle
        case washing
    }

    private(set) var state: State = .idle
    private let lock = NSRecursiveLock()

    func wash() {
        lock.lock()
        defer { lock.unlock() }

        if state == .washing {
            print("Already washing. Balking.")
            return
        }

        state = .washing
        print("Start washing")
        DispatchQueue.global().async {
            self.doWashing()
        }
    }

    private func doWashing() {
        Thread.sleep(forTimeInterval: 2) // Simulate washing
        lock.lock()
        defer { lock.unlock() }
        state = .idle
        print("Washing completed")
    }
}

In this example, we have a WashingMachine class with an internal State enum to represent its state, either idle or washing. The wash() method is called to initiate the washing process. We use a lock to ensure that only one thread can modify the state at a time.

When the wash() method is called while the washing machine is already in the washing state, it "balks" and returns immediately, printing "Already washing. Balking." to indicate that the operation was not performed.

Benefits

The Balking pattern can be useful in situations where it's undesirable to block the calling thread when an object is not ready to perform a requested action. By implementing the Balking pattern, you can improve your application's concurrency behavior and avoid potential issues caused by blocking on unavailable resources.

Conclusion

The Balking design pattern is a valuable tool for handling concurrency in your Swift applications. It helps you manage situations where an object's method is called when the object is not prepared to execute the requested action. By implementing the Balking pattern, you can ensure that your application responds gracefully to such situations, improving its overall concurrency behavior.