Deadlock with NSOutputStream and URLSessionUploadTask (__psynch_mutexwait)

Question

Our OSX app is uploading multiple files to the server using

func uploadTask(withStreamedRequest request: URLRequest) -> URLSessionUploadTask

While uploading, the upload gets stuck. Some files manage to upload successfully, sometimes more files other times less.

Looking at the debug navigator I can see that my stream thread shows two calls (one after the other; frame 11 and frame 5) to stream:handleEvent delegate, that points me to the code line where i call write:maxLength on NSOutputStrem , following __psynch_mutexwait in frame 0. At this point app is stuck and no network calls can finish executing.

Did anyone come across this issue? Any help is appreciated, thanks.

Answer 1

It looks like your handler is being signaled twice to write to the same stream. Add a check that the streamStatus is NSStreamStatusWriting and return early.