[Twisted-Python] Twisted VxWorks PBConnectionLost

[Toph Bei Fong]

Hello,

I started few days ago to make Buildbot under VxWorks run.
I ported Python and made a few changes in Buildbot and Twisted to make everything run.
I'm using Twisted 9.0.0 and Python 2.7.6
Twisted version is a bit old because its not complex as the 13.0.0 and it made the work under QNX for example.
In Buildbot there are few possibilities to make a Step:
	* FileUpload
	* FileDownload
	* ShellCommand
	* MasterShellCommand
MasterShellCommand doesnt make any difference here since its executed on the Master.
FileUpload and FileDownload (filetransfer between Master and Slave) works fine.

My Problem is the ShellCommand.
It executes a command on the Slave.
Im using the posix part on the Slave BUT fork() and exec() are not supported in VxWorks.
So i changed for _fork methode in twisted/internet/process.py to avoid the fork()-part [self.pid = fork()].
I didnt change the exec part in Twisted. I did in the Python .. (in os.py i changed the exec methode to call another methode .. so i didnt made a huge change there).

Now when i want to execute a ShellCommand, my buildbot/twisted/python crashes and i have an exception:
remoteFailed: [Failure instance: Traceback (failure with no frames): <class 'twisted.spread.pb.PBConnectionLost'>: [Failure instance: Traceback (failure with no frames): <class 'twisted.internet.error.ConnectionDone'>: Connection was closed cleanly.]

twisted.spread.pb.PBConnectionLost: [Failure instance: Traceback (failure with no frames): <class 'twisted.internet.error.ConnectionDone'>: Connection was closed cleanly. ]
twisted.spread.pb.PBConnectionLost: [Failure instance: Traceback (failure with no frames): <class 'twisted.internet.error.ConnectionDone'>: Connection was closed cleanly. ]

There are the two things i have.

My question after writing 40 lines here:
What could be the problem? 
Why does it just crash without any "real" exception or error.
Could someone point me to the right direction?

Thanks.

Best regards.
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