From f437c8d7e29a0df4fe77768085d697a72ac461c3 Mon Sep 17 00:00:00 2001
From: Jan Travnicek <Jan.Travnicek@fit.cvut.cz>
Date: Wed, 10 Aug 2016 13:41:33 +0200
Subject: [PATCH] background sub-process limiter
---
bash_multithread.sh | 84 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 84 insertions(+)
create mode 100755 bash_multithread.sh
diff --git a/bash_multithread.sh b/bash_multithread.sh
new file mode 100755
index 0000000000..6006b95b1c
--- /dev/null
+++ b/bash_multithread.sh
@@ -0,0 +1,84 @@
+#!/bin/bash
+
+# slightly modified implementation of sub-process limiter
+# by paxdiablo. See http://stackoverflow.com/a/1685440
+
+# bgxupdate - update active processes in a group.
+# Works by transferring each process to new group
+# if it is still active.
+# in: bgxgrp - current group of processes.
+# out: bgxgrp - new group of processes.
+# out: bgxcount - number of processes in new group.
+
+bgxupdate() {
+ bgxoldgrp=${bgxgrp}
+ bgxgrp=""
+ ((bgxcount = 0))
+ bgxjobs=" $(jobs -pr | tr '\n' ' ')"
+ for bgxpid in ${bgxoldgrp} ; do
+ echo "${bgxjobs}" | grep " ${bgxpid} " >/dev/null 2>&1
+ if [[ $? -eq 0 ]] ; then
+ bgxgrp="${bgxgrp} ${bgxpid}"
+ ((bgxcount = bgxcount + 1))
+ fi
+ done
+}
+
+# bgxlimit - start a sub-process with a limit.
+# Loops, calling bgxupdate until there is a free
+# slot to run another sub-process. Then runs it
+# an updates the process group.
+# in: $1 - the limit on processes.
+# in: $2+ - the command to run for new process.
+# in: bgxgrp - the current group of processes.
+# out: bgxgrp - new group of processes
+
+bgxlimit() {
+ bgxmax=$1 ; shift
+ bgxupdate
+ while [[ ${bgxcount} -ge ${bgxmax} ]] ; do
+ sleep 0.1
+ bgxupdate
+ done
+ if [[ "$1" != "-" ]] ; then
+ "$@" &
+ bgxgrp="${bgxgrp} $!"
+ fi
+ # echo '[' ${bgxgrp} ']'
+}
+
+# bgxwait - wait for sub-processes to finish
+# Loops calling bgxupdate until there is something
+# in a process group
+
+bgxwait() {
+ bgxupdate
+ while [[ ${bgxcount} -ne 0 ]] ; do
+ oldcount=${bgxcount}
+ while [[ ${oldcount} -eq ${bgxcount} ]] ; do
+ sleep 0.1
+ bgxupdate
+ done
+ # echo '[' ${bgxgrp} ']'
+ done
+}
+
+bgxtest() {
+ callback() {
+ id=$1 ; shift
+ echo start $id $(date | awk '{print $4}') "$BASHPID"
+ sleep ${id}0
+ echo end $id $(date | awk '{print $4}') "$BASHPID"
+ }
+
+ # Test program, create group and run 6 sleeps with
+ # limit of 3.
+
+ bgxgrp=""
+ for i in 1 2 3 4 5 6 ; do
+ bgxlimit 3 callback ${i}
+ done
+
+ # Wait until all others are finished.
+ bgxwait;
+}
--
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