[Mono-dev] Process.Start closing file descriptors

Robert Jordan robertj at gmx.net
Fri Jan 27 13:12:11 UTC 2012

On 27.01.2012 12:54, Weeble wrote:
> I have a program that uses
> System.IO.Pipes.AnonymousPipe{Server,Client}Stream on .NET to
> communicate between a parent and child process while still allowing
> the child process to use stdin, stdout and stderr normally. I've found
> that this part of System.IO.Pipes isn't implemented in Mono. From what
> I can tell, it shouldn't be especially hard to implement these classes
> themselves, but the critical problem would be that Process.Start
> explicitly closes all open file descriptors (except for stdin, stdout
> and stderr). The relevant code is here, in CreateProcess in
> processes.c:
> https://github.com/mono/mono/blob/master/mono/io-layer/processes.c#L988
> Because of that, I believe any working implementation of
> System.IO.Pipes.Anonymous* would require changes to CreateProcess.
> Either:
> 1. Remove entirely the loop that closes file descriptors.

This is out of question. For example, you don't want to share sockets.

> 2. Maintain a process-wide table of all file descriptors associated
> with the client-end of an AnonymousPipeServerStream, pass it into
> CreateProcess and skip closing of those file descriptors.

This is the way to go. The Win32 pipe functions must be simulated
by the io-layer similarly to the other I/O functions. This way
you'd know which handles to duplicate/inherit.


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