update

Task/Singleton/Objective-C/singleton-1.m

@@ -4,6 +4,6 @@
   // any instance variables
 }
 
-+ (SomeSingleton*)sharedInstance;
++ (SomeSingleton *)sharedInstance;
 
 @end

Task/Singleton/Objective-C/singleton-2.m

@@ -1,10 +1,10 @@
 // SomeSingleton.m
 @implementation SomeSingleton
 
-+ (SomeSingleton*) sharedInstance
++ (SomeSingleton *) sharedInstance
 {
-   static sharedInstance = nil;
-   if(!sharedInstance) {
+   static SomeSingleton *sharedInstance = nil;
+   if (!sharedInstance) {
       sharedInstance = [[SomeSingleton alloc] init];
    }
    return sharedInstance;
@@ -25,7 +25,7 @@
     return UINT_MAX;
 }
 
-- (void)release
+- (oneway void)release
 {
     // prevent release
 }

Task/Singleton/Objective-C/singleton-3.m

@@ -0,0 +1,10 @@
++ (SomeSingleton *) sharedInstance
+{
+   static SomeSingleton *sharedInstance = nil;
+   @synchronized(self) {
+      if (!sharedInstance) {
+         sharedInstance = [[SomeSingleton alloc] init];
+      }
+   }
+   return sharedInstance;
+}

Task/Singleton/Objective-C/singleton-4.m

@@ -0,0 +1,9 @@
++ (SomeSingleton *) sharedInstance
+{
+   static SomeSingleton *sharedInstance = nil;
+   static dispatch_once_t onceToken;
+   dispatch_once(&onceToken, ^{
+      sharedInstance = [[SomeSingleton alloc] init];
+   });
+   return sharedInstance;
+}