Atomic.swift

struct Atomic<T> {
  
  private var _value: T
  
  var value: T {
    mutating get {
      var result: T
      
      _atomic_lock_object(&self)
      result = _value
      _atomic_unlock_object(&self)
      
      return result
    }
    
    set {
      _atomic_lock_object(&self)
      _value = newValue
      _atomic_unlock_object(&self)
    }
  }
  
  init(_ value: T) {
    _value = value
  }
}

// AtomicLock.h (goes to the bridging header) 

#ifndef AtomicLock_h
#define AtomicLock_h

void _atomic_lock_object(void * _Nonnull object);
void _atomic_unlock_object(void * _Nonnull object);

#endif /* AtomicLock_h */


// AtomicLock.c
#include "AtomicLock.h"

#include <os/lock.h>

const int32_t GOODPOWER = 7;
const int32_t GOODMASK = (1 << GOODPOWER) - 1;

OS_ALWAYS_INLINE int32_t goodhash(int32_t value) {
  return (value >> 5) & GOODMASK;
}

static os_unfair_lock PropertyLocks[1 << GOODPOWER] = { 0 };

void _atomic_lock_object(void *object) {
  int32_t slot = goodhash((int32_t)object);
  os_unfair_lock_lock(&PropertyLocks[slot]);
}

void _atomic_unlock_object(void *object) {
  int32_t slot = goodhash((int32_t)object);
  os_unfair_lock_unlock(&PropertyLocks[slot]);
}