GCDObjC 0.3.0

GCDObjC 0.3.0

LangLanguage Obj-CObjective C
License MIT
ReleasedLast Release Jun 2016

Maintained by Mark Smith.

GCDObjC 0.3.0

  • By
  • Mark Smith

GCDObjC is an Objective-C wrapper for the most commonly used features of Grand Central Dispatch. It has four main aims:

  • Organize the flat C API into appropriate classes.
  • Use intention-revealing names to distinguish between synchronous and asynchronous functions.
  • Use more convenient arguments such as time intervals.
  • Add convenience methods.

A Swift port is at GCDSwift.


GCDObjC requires ARC and iOS 6.0. (Prior to 6.0, dispatch objects were not considered Objective-C objects, and therefore required manual memory management.)

GCDObjC.h is the only header file that needs to be imported.

For usage examples, see GCDObjCTests.m.

Install via CocoaPods:

pod "GCDObjC"


Queues are implemented in the GCDQueue class.

  • convenience accessors for global queues
+ (GCDQueue *)mainQueue;
+ (GCDQueue *)globalQueue;
+ (GCDQueue *)highPriorityGlobalQueue;
+ (GCDQueue *)lowPriorityGlobalQueue;
+ (GCDQueue *)backgroundPriorityGlobalQueue;
  • testing the current execution context
+ (BOOL)isMainQueue;
  • creating serial and concurrent queues
- (instancetype)initSerial;
- (instancetype)initConcurrent;
  • queueing blocks for asynchronous execution
- (void)queueBlock:(dispatch_block_t)block;
- (void)queueBlock:(dispatch_block_t)block afterDelay:(double)seconds;
- (void)queueBlock:(dispatch_block_t)block inGroup:(GCDGroup *)group;
  • queueing blocks for synchronous execution
- (void)queueAndAwaitBlock:(dispatch_block_t)block;
- (void)queueAndAwaitBlock:(void (^)(size_t))block iterationCount:(size_t)count;
  • queueing barrier blocks for synchronous or asynchronous execution
- (void)queueBarrierBlock:(dispatch_block_t)block;
- (void)queueAndAwaitBarrierBlock:(dispatch_block_t)block;
  • queueing notify blocks on groups
- (void)queueNotifyBlock:(dispatch_block_t)block inGroup:(GCDGroup *)group;
  • suspending and resuming a queue
- (void)suspend;
- (void)resume;
  • associating context data with a key
- (void *)contextForKey:(const void *)key;
- (void)setContext:(void *)context forKey:(const void *)key;


Semaphores are implemented in the GCDSemaphore class.

  • creating semaphores
- (instancetype)init;
- (instancetype)initWithValue:(long)value;
  • signaling and waiting on a semaphore
- (BOOL)signal;
- (void)wait;
- (BOOL)wait:(double)seconds;


Groups are implemented in the GCDGroup class.

  • creating groups
- (instancetype)init;
  • entering and leaving a group
- (void)enter;
- (void)leave;
  • waiting on completion of a group
- (void)wait;
- (BOOL)wait:(double)seconds;


Two macros are provided for wrapping dispatch_once() calls.

  • executing a block only once: GCDExecOnce(block)
for (int i = 0; i < 10; ++i) {
    GCDExecOnce(^{ NSLog(@"This will only be logged once."); });
  • creating a singleton instance of a class: GCDSharedInstance(block)
+ (instancetype)sharedInstance {
  GCDSharedInstance(^{ return [self new]; });

The block supplied to GCDSharedInstance() must return an instance of the desired class.