Simple synchronization functions for Swift, wrapping the Cocoa NSLocking classes

locking.swift

import Foundation

/// Protocol for NSLocking objects that also provide tryLock()
public protocol TryLockable: NSLocking {
    func tryLock() -> Bool
}

// These Cocoa classes have tryLock()
extension NSLock: TryLockable {}
extension NSRecursiveLock: TryLockable {}
extension NSConditionLock: TryLockable {}


/// Protocol for NSLocking objects that also provide lockBeforeDate()
public protocol BeforeDateLockable: NSLocking {
    func lockBeforeDate(limit: NSDate) -> Bool
}

// These Cocoa classes have lockBeforeDate()
extension NSLock: BeforeDateLockable {}
extension NSRecursiveLock: BeforeDateLockable {}
extension NSConditionLock: BeforeDateLockable {}


/// Use an NSLocking object as a mutex for a critical section of code
public func synchronized<L: NSLocking>(lockable: L, criticalSection: () -> ()) {
    lockable.lock()
    criticalSection()
    lockable.unlock()
}

/// Use an NSLocking object as a mutex for a critical section of code that returns a result
public func synchronizedResult<L: NSLocking, T>(lockable: L, criticalSection: () -> T) -> T {
    lockable.lock()
    let result = criticalSection()
    lockable.unlock()
    return result
}

/// Use a TryLockable object as a mutex for a critical section of code
///
/// Return true if the critical section was executed, or false if tryLock() failed
public func trySynchronized<L: TryLockable>(lockable: L, criticalSection: () -> ()) -> Bool {
    if !lockable.tryLock() {
        return false
    }
    criticalSection()
    lockable.unlock()
    return true
}

/// Use a BeforeDateLockable object as a mutex for a critical section of code
///
/// Return true if the critical section was executed, or false if lockBeforeDate() failed
public func synchronizedBeforeDate<L: BeforeDateLockable>(limit: NSDate, lockable: L, criticalSection: () -> ()) -> Bool {
    if !lockable.lockBeforeDate(limit) {
        return false
    }
    criticalSection()
    lockable.unlock()
    return true
}


// Examples

let lock = NSLock()

synchronized(lock) {
    println("This is synchronized")
}

let result: String = synchronizedResult(lock) {
    return "This is synchronized"
}

let didRun = trySynchronized(lock) {
    println("This was synchronized with a trySynchronized")
}
println("didRun: \(didRun)")

let limit = NSDate(timeIntervalSinceNow: 1.0)
let didRunBeforeDate = synchronizedBeforeDate(limit, lock) {
    println("This was synchronized with a time limit");
}
println("didRunBeforeDate: \(didRunBeforeDate)")


let recursiveLock = NSRecursiveLock()

synchronized(recursiveLock) {
    println("This is synchronized with a recursive lock")
    synchronized(recursiveLock) {
        println("This is synchronized with the same recursive lock")
    }
}

Thank you for the great and simple functions.

I think you might need to use @NoEscape for the passed closures.

I've updated this for Swift 3 here: https://gist.github.com/einsteinx2/00b9ebd962f3a0f6c9e758f842e4c6f9

@mohamede1945: @NoEscape is no longer necessary as it's the default in Swift 3 and is deprecated.