void dispatch_group_async(
dispatch_group_t group,
dispatch_queue_t queue,
dispatch_block_t block );
void dispatch_group_async_f(
dispatch_group_t group,
dispatch_queue_t queue,
void *context,
dispatch_function_t work );
void dispatch_group_notify(
dispatch_group_t group,
dispatch_queue_t queue,
dispatch_block_t block );
void dispatch_group_notify_f(
dispatch_group_t group,
dispatch_queue_t queue,
void *context,
dispatch_function_t work );
long dispatch_group_wait(
dispatch_group_t group,
dispatch_time_t timeout );