04-14-2010
Thanks, Franklin52, that's precisely what I had in mind, but what I was actually getting at was the safety of this technique.
I know that multiple processes writing to the same file is a recipe for trouble, understandably, but I was curious whether multiple jobs/processes reading from the same file is also dangerous.
For example, what happens if they both try to read the same block of memory at the same time?
My googling turned up some forum topics about this in C code, where it did seem to be an issue, but I was going to submit jobs to the background like in Franklin52's post. Can I rely on the OS to sort out any conflicts between the processes?
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LEARN ABOUT POSIX
queuedefs
queuedefs(4) File Formats queuedefs(4)
NAME
queuedefs - queue description file for at, batch, and cron
SYNOPSIS
/etc/cron.d/queuedefs
DESCRIPTION
The queuedefs file describes the characteristics of the queues managed by cron(1M). Each non-comment line in this file describes one queue.
The format of the lines are as follows:
q.[njobj][nicen][nwaitw]
The fields in this line are:
q The name of the queue. a is the default queue for jobs started by at(1); b is the default queue for jobs started by batch (see
at(1)); c is the default queue for jobs run from a crontab(1) file.
njob The maximum number of jobs that can be run simultaneously in that queue; if more than njob jobs are ready to run, only the first
njob jobs will be run, and the others will be run as jobs that are currently running terminate. The default value is 100.
nice The nice(1) value to give to all jobs in that queue that are not run with a user ID of super-user. The default value is 2.
nwait The number of seconds to wait before rescheduling a job that was deferred because more than njob jobs were running in that job's
queue, or because the system-wide limit of jobs executing has been reached. The default value is 60.
Lines beginning with # are comments, and are ignored.
EXAMPLES
Example 1: A sample file.
#
#
a.4j1n
b.2j2n90w
This file specifies that the a queue, for at jobs, can have up to 4 jobs running simultaneously; those jobs will be run with a nice value
of 1. As no nwait value was given, if a job cannot be run because too many other jobs are running cron will wait 60 seconds before trying
again to run it.
The b queue, for batch(1) jobs, can have up to 2 jobs running simultaneously; those jobs will be run with a nice(1) value of 2. If a job
cannot be run because too many other jobs are running, cron(1M) will wait 90 seconds before trying again to run it. All other queues can
have up to 100 jobs running simultaneously; they will be run with a nice value of 2, and if a job cannot be run because too many other jobs
are running cron will wait 60 seconds before trying again to run it.
FILES
/etc/cron.d/queuedefs queue description file for at, batch, and cron.
SEE ALSO
at(1), crontab(1), nice(1), cron(1M)
SunOS 5.10 1 Mar 1994 queuedefs(4)