why pinging run with mainthread? in children thread will call bug?
The code :

• (void)pingWithBlock:(void (^)(BOOL isSuccess, NSTimeInterval latency))completion
  {
  //NSLog(@"pingWithBlock");
  if (completion)
  {
  // copy the block, then added to the blocks array.
  @synchronized(self)
  {
  [self.completionBlocks addObject:[completion copy]];
  }
  }

  if (!self.isPinging)
  {
  // MUST make sure pingFoundation in mainThread
  __weak __typeof(self)weakSelf = self;
  if (![[NSThread currentThread] isMainThread]) {
  dispatch_sync(dispatch_get_main_queue(), ^{
  __strong __typeof(weakSelf)strongSelf = weakSelf;
  [strongSelf startPing];
  });
  }
  else
  {
  [self startPing];
  }
  }
  }