SEM(1) parallel SEM(1)NAMEsem - semaphore for executing shell command lines in parallel
SYNOPSISsem [--fg] [--id <id>] [--semaphoretimeout <secs>] [-j <num>] [--wait]
command
DESCRIPTION
GNU sem is an alias for GNU parallel --semaphore.
GNU sem acts as a counting semaphore. When GNU sem is called with
command it starts the command in the background. When num number of
commands are running in the background, GNU sem waits for one of these
to complete before starting the command.
GNU sem does not read any arguments to build the command (no -a, :::,
and ::::). It simply waits for a semaphore to become available and then
runs the command given.
Before looking at the options you may want to check out the examples
after the list of options. That will give you an idea of what GNU sem
is capable of.
OPTIONS
command Command to execute. The command may be followed by arguments
for the command.
--bg Run command in background thus GNU sem will not wait for
completion of the command before exiting. This is the default.
In toilet analogy: GNU sem waits for a toilet to be available,
gives the toilet to a person, and exits immediately.
See also: --fg
--jobs N
-j N
--max-procs N
-P N Run up to N commands in parallel. Default is 1 thus acting
like a mutex.
In toilet analogy: -j is the number of toilets.
--jobs +N
-j +N
--max-procs +N
-P +N Add N to the number of CPU cores. Run up to this many jobs in
parallel. For compute intensive jobs -j +0 is useful as it
will run number-of-cpu-cores jobs simultaneously.
--jobs -N
-j -N
--max-procs -N
-P -N Subtract N from the number of CPU cores. Run up to this many
jobs in parallel. If the evaluated number is less than 1 then
1 will be used. See also --use-cpus-instead-of-cores.
--jobs N%
-j N%
--max-procs N%
-P N% Multiply N% with the number of CPU cores. Run up to this many
jobs in parallel. If the evaluated number is less than 1 then
1 will be used. See also --use-cpus-instead-of-cores.
--jobs procfile
-j procfile
--max-procs procfile
-P procfile
Read parameter from file. Use the content of procfile as
parameter for -j. E.g. procfile could contain the string 100%
or +2 or 10.
--semaphorename name
--id name
Use name as the name of the semaphore. Default is the name of
the controlling tty (output from tty).
The default normally works as expected when used
interactively, but when used in a script name should be set.
$$ or my_task_name are often a good value.
The semaphore is stored in ~/.parallel/semaphores/
In toilet analogy the name corresponds to different types of
toilets: e.g. male, female, customer, staff.
--fg Do not put command in background.
In toilet analogy: GNU sem waits for a toilet to be available,
takes a person to the toilet, waits for the person to finish,
and exits.
--semaphoretimeout secs (beta testing)
--st secs (beta testing)
If secs > 0: If the semaphore is not released within secs
seconds, take it anyway.
If secs < 0: If the semaphore is not released within secs
seconds, exit.
In toilet analogy: secs > 0: If no toilet becomes available
within secs seconds, pee on the floor. secs < 0: If no toilet
becomes available within secs seconds, exit without doing
anything.
--wait Wait for all commands to complete.
In toilet analogy: Wait until all toilets are empty, then
exit.
UNDERSTANDING A SEMAPHORE
Try the following example:
sem-j 2 'sleep 1;echo 1 finished'; echo sem 1 exited
sem-j 2 'sleep 2;echo 2 finished'; echo sem 2 exited
sem-j 2 'sleep 3;echo 3 finished'; echo sem 3 exited
sem-j 2 'sleep 4;echo 4 finished'; echo sem 4 exited
sem --wait; echo sem--wait done
In toilet analogy this uses 2 toilets (-j 2). GNU sem takes '1' to a
toilet, and exits immediately. While '1' is sleeping, another GNU sem
takes '2' to a toilet, and exits immediately.
While '1' and '2' are sleeping, another GNU sem waits for a free
toilet. When '1' finishes, a toilet becomes available, and this GNU sem
stops waiting, and takes '3' to a toilet, and exits immediately.
While '2' and '3' are sleeping, another GNU sem waits for a free
toilet. When '2' finishes, a toilet becomes available, and this GNU
sem stops waiting, and takes '4' to a toilet, and exits immediately.
Finally another GNU sem waits for all toilets to become free.
EXAMPLE: Gzipping *.log
Run one gzip process per CPU core. Block until a CPU core becomes
available.
for i in *.log ; do
echo $i
sem -j+0 gzip $i ";" echo done
done
sem--wait
EXAMPLE: Protecting pod2html from itself
pod2html creates two files: pod2htmd.tmp and pod2htmi.tmp which it does
not clean up. It uses these two files for a short time. But if you run
multiple pod2html in parallel (e.g. in a Makefile with make -j) there
is a risk that two different instances of pod2html will write to the
files at the same time:
# This may fail due to shared pod2htmd.tmp/pod2htmi.tmp files
foo.html:
pod2html foo.pod --outfile foo.html
bar.html:
pod2html bar.pod --outfile bar.html
$ make -j foo.html bar.html
You need to protect pod2html from running twice at the same time. sem
running as a mutex will make sure only one runs:
foo.html:
sem--id pod2html pod2html foo.pod --outfile foo.html
bar.html:
sem--id pod2html pod2html bar.pod --outfile bar.html
clean: foo.html bar.html
sem--id pod2html --wait
rm -f pod2htmd.tmp pod2htmi.tmp
$ make -j foo.html bar.html clean
BUGS
None known.
REPORTING BUGS
Report bugs to <bug-parallel@gnu.org>.
AUTHOR
Copyright (C) 2010,2011,2012,2013 Ole Tange, http://ole.tange.dk and
Free Software Foundation, Inc.
LICENSE
Copyright (C) 2010,2011,2012,2013 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 3 of the License, or at your
option any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License along
with this program. If not, see <http://www.gnu.org/licenses/>.
Documentation license I
Permission is granted to copy, distribute and/or modify this
documentation under the terms of the GNU Free Documentation License,
Version 1.3 or any later version published by the Free Software
Foundation; with no Invariant Sections, with no Front-Cover Texts, and
with no Back-Cover Texts. A copy of the license is included in the
file fdl.txt.
Documentation license II
You are free:
to Share to copy, distribute and transmit the work
to Remix to adapt the work
Under the following conditions:
Attribution
You must attribute the work in the manner specified by the
author or licensor (but not in any way that suggests that they
endorse you or your use of the work).
Share Alike
If you alter, transform, or build upon this work, you may
distribute the resulting work only under the same, similar or
a compatible license.
With the understanding that:
Waiver Any of the above conditions can be waived if you get
permission from the copyright holder.
Public Domain
Where the work or any of its elements is in the public domain
under applicable law, that status is in no way affected by the
license.
Other Rights
In no way are any of the following rights affected by the
license:
· Your fair dealing or fair use rights, or other applicable
copyright exceptions and limitations;
· The author's moral rights;
· Rights other persons may have either in the work itself or
in how the work is used, such as publicity or privacy
rights.
Notice For any reuse or distribution, you must make clear to others
the license terms of this work.
A copy of the full license is included in the file as cc-by-sa.txt.
DEPENDENCIES
GNU sem uses Perl, and the Perl modules Getopt::Long, Symbol, Fcntl.
SEE ALSOparallel(1)20150722 2015-08-16 SEM(1)
