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- Subject: Re: pipe to a pubprocess, or tmpfile
- From: Joshua Phillips <jp.sittingduck@...>
- Date: Wed, 08 Sep 2010 11:51:01 +0100
On 07/09/10 12:41, email@example.com wrote:
Due to the shortcomings of Lua's support for creating child processes, I
started a Lua module for doing this, modelled loosely on Python's
subprocess module. It is able to create child processes with pipe/file
redirection, and it can wait/poll for child processes. It can use POSIX
(fork/exec) or the Windows API.
OK, one more on the subject:
Problem is, popen
doesn't give you the return value of the command you ran.
The good news is that closing the handle from io.popen in
Lua 5.2 does give you the return code.
That it means p:close waits for the command to finish:
local p = assert(io.popen('aplaymidi -', 'w'))
p:write(my_midi) -- fast; the MIDI is compact :-)
p:close() -- waits several minutes :-(
Is there a way of letting aplaymidi run on in the background?
p = io.popen('aplaymidi -&', 'w')
- is not a Standard MIDI File (it's empty :-( )
and I get the same message from:
io.popen('sh -c "aplaymidi -"&', 'w')
and likewise at the command-line:
cat t.mid | sh -c 'aplaymidi -&'
Although at the command-line:
cat t.mid | sh -c "aplaymidi -"&
works as intended, so by now I'm starting to get confused...
Is there a right way to background the aplaymidi process ?
Regards, Peter Billam
http://www.pjb.com.au firstname.lastname@example.org (03) 6278 9410
"Was der Meister nicht kann, vermÃcht es der Knabe, hÃtt er
ihm immer gehorcht?" Siegfried to Mime, from Act 1 Scene
The 'subprocess.wait' function, which waits for any child process to
finish, doesn't work very well in a multi-threaded POSIX environment,
because I can't give the POSIX 'wait' function a list of pids to wait
for: if 'wait' returns a pid for which there's no Lua object ('alien
pid'), the process has already been removed from the process table and
there's little I can do.
I'm working on a locked global data structure to store alien pids, but
that won't help if other parts of the process are using wait or waitpid.
Apart from those shortcomings with subprocess.wait (which don't apply to
Windows because there is WaitForMultipleObjects), it works quite well.
Code and documentation are in this repository: