Atomic property in Swift using ReadWriteLock. See blog post for more details: http://www.vadimbulavin.com/atomic-properties/

ReadWriteLockAtomicProperty.swift

final class ReadWriteLock {
    private var rwlock: pthread_rwlock_t = {
        var rwlock = pthread_rwlock_t()
        pthread_rwlock_init(&rwlock, nil)
        return rwlock
    }()
    
    func writeLock() {
        pthread_rwlock_wrlock(&rwlock)
    }
    
    func readLock() {
        pthread_rwlock_rdlock(&rwlock)
    }
    
    func unlock() {
        pthread_rwlock_unlock(&rwlock)
    }
}

class ReadWriteLockAtomicProperty {
    private var underlyingFoo = 0
    private let lock = ReadWriteLock()
    
    var foo: Int {
        get {
            lock.readLock()
            let value = underlyingFoo
            lock.unlock()
            return value
        }
        set {
            lock.writeLock()
            underlyingFoo = newValue
            lock.unlock()
        }
    }
}