Re: [PATCH] Add facility to collect stderr of async subprocess

[Paul Eggert]

I took a quick look, and in the ordinary POSIXish code there's a race 
condition between the calls to pipe2 and the calls to fcntl with 
FD_CLOEXEC.  If some other thread forks and execs a process after pipe2 
but before fcntl, that process will have access to the pipe ends and 
this could cause problems.  Instead, please call pipe2 (.., O_BINARY | 
O_CLOEXEC) so that the other process won't see the pipe end.  Any child 
process that needs to have the pipe end survive an exec should then call 
fcntl (pipe_end, F_SETFD, 0) before execing.  This is how the existing 
Emacs code works.  So, there should be no need to call fcntl (inchannel, 
F_SETFD, FD_CLOEXEC) and likewise for outchannel.