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.

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.

Queues are implemented in the GCDQueue class.

• convenience accessors for global queues

+ (GCDQueue *)mainQueue;
+ (GCDQueue *)globalQueue;
+ (GCDQueue *)highPriorityGlobalQueue;
+ (GCDQueue *)lowPriorityGlobalQueue;
+ (GCDQueue *)backgroundPriorityGlobalQueue;

• 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;

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 class] new]; });
}

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