03-25-2004
In other words, the children are doing nothing while waiting for the parent's notification. I agree that you will need a semaphore then, because the order in which signals are handled cannot be enforced in a reliable manner without resorting to changing scheduling policies, which is definitely not justified in this case.
I would probably do this:
Have each child install a signal handler for SIGUSR1, without restarting interrupted system calls. Have a loop calling pause() for the desired number of times the PID shall be written. After the parent has signaled the current child, it goes to sleep on a semaphore. After the child has written its PID to the file, it awakes the parent by incrementing the semaphore and calls pause() again. The parent goes on to signal the next child, and so on. Good luck
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LEARN ABOUT XFREE86
renice
RENICE(1) User Commands RENICE(1)
NAME
renice - alter priority of running processes
SYNOPSIS
renice [-n] priority [-g|-p|-u] identifier...
DESCRIPTION
renice alters the scheduling priority of one or more running processes. The first argument is the priority value to be used. The other
arguments are interpreted as process IDs (by default), process group IDs, user IDs, or user names. renice'ing a process group causes all
processes in the process group to have their scheduling priority altered. renice'ing a user causes all processes owned by the user to have
their scheduling priority altered.
OPTIONS
-n, --priority priority
Specify the scheduling priority to be used for the process, process group, or user. Use of the option -n or --priority is optional,
but when used it must be the first argument.
-g, --pgrp
Interpret the succeeding arguments as process group IDs.
-p, --pid
Interpret the succeeding arguments as process IDs (the default).
-u, --user
Interpret the succeeding arguments as usernames or UIDs.
-V, --version
Display version information and exit.
-h, --help
Display help text and exit.
EXAMPLES
The following command would change the priority of the processes with PIDs 987 and 32, plus all processes owned by the users daemon and
root:
renice +1 987 -u daemon root -p 32
NOTES
Users other than the superuser may only alter the priority of processes they own. Furthermore, an unprivileged user can only increase the
``nice value'' (i.e., choose a lower priority) and such changes are irreversible unless (since Linux 2.6.12) the user has a suitable
``nice'' resource limit (see ulimit(1) and getrlimit(2)).
The superuser may alter the priority of any process and set the priority to any value in the range -20 to 19. Useful priorities are: 19
(the affected processes will run only when nothing else in the system wants to), 0 (the ``base'' scheduling priority), anything negative
(to make things go very fast).
FILES
/etc/passwd
to map user names to user IDs
SEE ALSO
nice(1), getpriority(2), setpriority(2), credentials(7), sched(7)
HISTORY
The renice command appeared in 4.0BSD.
AVAILABILITY
The renice command is part of the util-linux package and is available from Linux Kernel Archive <https://www.kernel.org/pub/linux/utils
/util-linux/>.
util-linux July 2014 RENICE(1)