Texture GCD

a%3d230%26b%3d1290%26c%3d819

// dispatch once macro
#define ASCreateOnce(expr) ({ \
  static dispatch_once_t onceToken; \
  static __typeof__(expr) staticVar; \
  dispatch_once(&onceToken, ^{ \
    staticVar = expr; \
  }); \
  staticVar; \
})

// like dispatch_apply , 可以自定义 thread count, 设计思路ok
void ASDispatchApply(size_t iterationCount, dispatch_queue_t queue, NSUInteger threadCount, NS_NOESCAPE void(^work)(size_t i)) {
  if (threadCount == 0) {
    if (ASActivateExperimentalFeature(ASExperimentalDispatchApply)) {
      dispatch_apply(iterationCount, queue, work);
      return;
    }
    threadCount = NSProcessInfo.processInfo.activeProcessorCount * 2;
  }
  dispatch_group_t group = dispatch_group_create();
  __block atomic_size_t counter = ATOMIC_VAR_INIT(0);
  for (NSUInteger t = 0; t < threadCount; t++) {
    dispatch_group_async(group, queue, ^{
      size_t i;
      while ((i = atomic_fetch_add(&counter, 1)) < iterationCount) {
        work(i);
      }
    });
  }
  dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
};

// set queue target 
dispatch_queue_create("org.AsyncDisplayKit.ASDisplayLayer.displayQueue", DISPATCH_QUEUE_CONCURRENT);
    // we use the highpri queue to prioritize UI rendering over other async operations
    dispatch_set_target_queue(displayQueue, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0));

// check main thread
ASDisplayNodeThreadIsMain()
{
  return 0 != pthread_main_np();
}

总结:主线程判断, 设置target queue, 自定义实现 dispatch_apply 的功能.