[BFTask waitUntilFinished] wait forever.

[ufosky]

I write this testcase for reproduce my issue.When runs to line [BFTask waitUntilFinished], it cannot return.

- (void)testAsyncWait {
  NSLog(@"Start call");
  BFExecutor *backgroundExecutor = [BFExecutor executorWithDispatchQueue:dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0)];
  BFTask *task = [[[BFTask taskFromExecutor:backgroundExecutor withBlock:^id(BFTask *task) {
    NSLog(@"Background call");
    return nil;
  }] continueWithSuccessBlock:^id(BFTask *task) {
    NSLog(@"Background call2");
    return nil;
  }] continueWithExecutor:[BFExecutor mainThreadExecutor] withSuccessBlock:^id(BFTask *task) {
    NSLog(@"Foreground call");
    return @"Test Result";
  }];
  NSLog(@"Wait call");
  [task waitUntilFinished];
  NSLog(@"End call");
  NSLog(@"%@", task.result);
}

[ufosky]

I write an alternative implemention of [BFTask waitUntilFinished] for solve this issue:

- (void)waitUntilFinished {
  if ([NSThread isMainThread]) {
    [self warnOperationOnMainThread];
  }
  BOOL finished = NO;
  while (!finished) {
    @autoreleasepool {
      [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode
                               beforeDate:[NSDate dateWithTimeIntervalSinceNow:0.01]];
      @synchronized(self.lock) {
        if (self.completed) {
          finished = YES;
          continue;
        }
        [self.condition lock];
      }
      NSDate *date = [NSDate dateWithTimeIntervalSinceNow:0.01];
      finished = [self.condition waitUntilDate:date];
      [self.condition unlock];
    }
  }
}

[nlutsenko]

This sounds about right...
The problem is that a lot of threads usually don't have a run loop attached to them, in addition - I suspect that your wait on condition is changing the flow of waiting, since it is going to bailout early without waiting for a condition to be met if the wait exceeds 0.01s.

We are improving this flow in #135, but that would still leave the spinning the run loop out. I am open to ideas on this. cc @toddreed

[nlutsenko]

Closing as per no activity and this is working as intended.
@ufosky, let me know if you think this is actionable in some way.
But general suggestion - avoid calling waitUntilFinished at all costs, especially on the main thread.