On Sun, Feb 08, 2009 at 07:58:51AM -0500, "Douglas A. Tutty" <dtu...@vianet.ca> was heard to say: > On Sun, Feb 08, 2009 at 05:52:34PM +1000, Adrian Levi wrote: > > 2009/2/8 Daniel Burrows <dburr...@debian.org>: > > > Hello list, > > > > > > I've been banging my head on this one for a while. > > > > > > I have a need to write some code that can manage job control on a > > > terminal. More specifically, I need to run a single process and stuff > > > it into the background at will, so that it gets suspended when it tries > > > to read from the terminal. So, there's a "controller" process and > > > a "subprocess" process. > > > > > > controller ----------> subprocess > > > manages > > Is the single process a black box or are you writing it too? If its not > a black box, can't its reads from the terminal just sit and wait for > input (or test a semiphor before doing anything with the terminal)?
The part that reads from the terminal is a black box -- it could be anything invoked by a dpkg maintainer script. > If it is a black box, what happens if it tries to read from std-in if > std-in doesn't have anything? After I sent the mail, I figured out that if it ever *actually* tries to read from stdin, it gets stopped. The problem is that the program I was testing with apparently blocks in select() instead of reading outright, and select() doesn't trigger SIGTTIN; it has to issue a read(). > Perhaps your controller program will have > to be a filter between the process and the terminal: pipe its std-in an > std-out to the controller process and the controller process issue the > appropriate shell start/stop commands as necessary while leaving the > process in the background the whole time. I thought about this option, but the problem is detecting when the subprocess is trying to read (but I don't have anything to give it). One interesting idea I got from the libc manual (but have yet to follow up on) is to inject a VDSUSP character into the stream -- apparently this will suspend the process, but only when the character is actually read. I vaguely recall having some reason to think it might not work, but it's worth at least trying. (as it happens, since I control the terminal, I don't need a man in the middle to do this (I think) -- I can just ask the terminal to send the character) Daniel -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
