[Interest] Qt 5.6.0: Strange "QProcess: CreateNamedPipe failed. (access denied)" messages

[Rainer Wiesenfarth]

This is my situation:

I have two applications, lets call them Dad and Son, both of them using Qt
(in my case: 5.6.0). Dad starts multiple instances of Son, using QProcess.

I use two different environments:

Environment 1: Windows 10.
- Dad starts first instance of Son => error message from Qt "QProcess:
CreateNamedPipe failed. (access denied)" (3 times)
- first Son's output is not caught in Dad, but Son runs as expected.
- Any subsequent instance of Son started by Dad works fine,
- there is no more error messages and
- Son's output is caught by Dad.

Environment 2: Windows 7.
- Dad starts first instance of Son => no error
- first Son's output is caught in Dad and Sun runs as expected.
​- Any subsequent instance of Son started by Dad works fine,
- there is no error messages and
- Son's output is caught by Dad.
​
In case this matters: Dad creates and starts the QProcess instances in a
separate thread, not in the main /GUI thread.

Does anyone of you have an idea what happens and how it can be prevented?

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