marwood@ncs.dnd.ca (Gordon Marwood) (07/19/90)
I am in the process of converting a Bourne shell script to C, and I am
having trouble finding out how to identify and kill background
processes. With the Bourne Shell approach this was simple, using $!.
What I would like to do is start a background process at one point in the
C program, and at a later time kill it. Currently I am invoking the
background process with system("background_process &");, but none of the
texts that I have available help me to proceed any further.
Any assistance would be appreciated.
Gordon Marwood
Internet: marwood@ncs.dnd.cadkeisen@Gang-of-Four.Stanford.EDU (Dave Eisen) (07/20/90)
In article <1990Jul19.151728.17448@ncs.dnd.ca> marwood@ncs.dnd.ca (Gordon Marwood) writes: > >What I would like to do is start a background process at one point in the >C program, and at a later time kill it. Currently I am invoking the >background process with system("background_process &");, but none of the >texts that I have available help me to proceed any further. > System is not a powerful enough tool for this, it is designed for only the simplest of process control situations. You'll have to fork and exec the new process yourself. Fork will create a new process and return the pid of that process, at some later point use kill (pid, signal_number) to kill it. For more details, drop me a note or (better still) pick up a copy of Marc Rochkind's Advanced Unix Programming. (BTW -- even though it is a UNIX book and not a C book, I think it should be mentioned in the Frequently Asked Questions posting as an excellent reference for C programming under UNIX.) Followups redirected to comp.unix.questions. -- Dave Eisen Home: (415) 323-9757 dkeisen@Gang-of-Four.Stanford.EDU Office: (415) 967-5644 1447 N. Shoreline Blvd. Mountain View, CA 94043
larrym@pi19.pnfi.forestry.ca (Larry Marshall) (07/20/90)
marwood@ncs.dnd.ca (Gordon Marwood) writes: >What I would like to do is start a background process at one point in the >C program, and at a later time kill it. Currently I am invoking the >background process with system("background_process &");, but none of the >texts that I have available help me to proceed any further. The latest Computer Language (July) has an article on manipulating Unix processes in C. It discusses the monitoring of PIDs and includes code for terminating those processes. Larry Marshall Petawawa National Forestry Institute
venkat@matrix.UUCP (D Venkatrangan) (07/27/90)
In article <1990Jul19.151728.17448@ncs.dnd.ca> marwood@ncs.dnd.ca (Gordon Marwood) writes: >I am in the process of converting a Bourne shell script to C, and I am >having trouble finding out how to identify and kill background >processes. With the Bourne Shell approach this was simple, using $!. > >What I would like to do is start a background process at one point in the >C program, and at a later time kill it. Currently I am invoking the >background process with system("background_process &");, but none of the >texts that I have available help me to proceed any further. > >Any assistance would be appreciated. > Instead of system(), try using vfork() followed by execlp(). In foreground program, do something like: if ((child_pid = vfork()) == -1) perror("vfork failed"); if (child_pid == 0) { execlp(execfile, execfile, arg1, arg2, ..., (char *)0); /* should not return */ perror("exec failed"); } /* parent */ /* if we get killed... */ (void)signal(SIGINT, kill_child); /* call kill_child() to send a user defined signal to child. */ /* or just call kill(child_pid, SIGUSR1); */ void kill_child(sigval) int sigval; { if (sigval == SIGINT) kill(child_pid, SIGUSR1); } In child, during initialization do: (void)signal(SIGUSR1, childsighandler); and define: void childsighandler(sigval) int sigval; { if (sigval == SIGUSR1) { /* the parent is sending something */ cleanup(); exit(); } }