Obj-c singleton

gistfile1.m

//
// Non-thread safe
//
@interface MySingleton : NSObject
{
}

+ (MySingleton *)sharedSingleton;
@end

@implementation MySingleton

+ (MySingleton *)sharedSingleton
{
  static MySingleton *sharedSingleton;

  @synchronized(self)
  {
    if (!sharedSingleton)
      sharedSingleton = [[MySingleton alloc] init];

    return sharedSingleton;
  }
}
@end

//
// Thread safe
//
+(MyClass *)sharedInstance
{   
    static MyClass *sharedInstance = nil;
    static dispatch_once_t pred;

    dispatch_once(&pred, ^{
        sharedInstance = [[MyClass alloc] init];
    });

    return sharedInstance;
}


//
// Macro. Thread safe.
//
/*!
 * @function Singleton GCD Macro
 */
#ifndef SINGLETON_GCD
#define SINGLETON_GCD(classname)                            \
                                                            \
+ (classname *)shared##classname {                          \
                                                            \
    static dispatch_once_t pred;                            \
    static classname * shared##classname = nil;             \
    dispatch_once( &pred, ^{                                \
      shared##classname = [[self alloc] init];              \
    });                                                     \
      return shared##classname;                             \
}                                                           
#endif