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    <h2><em>Rendez-vous</em></h2> <p>If you wanna have two independant process which could communicate, you have to place a <em>rendez-vous</em> somewhere both process can reach.</p> <p>This could be a simple file, a fifo pipe, a unix socket, a TCP socket or maybe else (Rexx port).</p> <h2><a href="/questions/tagged/bash" class="post-tag" title="show questions tagged &#39;bash&#39;" rel="tag">bash</a> and other <a href="/questions/tagged/shell" class="post-tag" title="show questions tagged &#39;shell&#39;" rel="tag">shell</a></h2> <p>Bash don't have a equivalent to rexx port, so there is a little sample, using a rendez-vous file, that work (on my Linux).</p> <p>I'm using <em>shared memory</em> <code>/dev/shm</code>, to reduce disk load.</p> <h3>Simple counter sample</h3> <pre><code>$ back_func() { while :;do echo $(($(&lt;/dev/shm/foo)+1)) &gt;/dev/shm/foo; sleep .3; done; } </code></pre> <p>Let play</p> <pre><code>$ echo 1 &gt;/dev/shm/foo $ back_func &amp; $ echo $(&lt;/dev/shm/foo) 4 $ echo $(&lt;/dev/shm/foo) 21 </code></pre> <p>Than stop now:</p> <pre><code>$ fg back_func ^C </code></pre> <p>or</p> <pre><code>$ kill $! $ [1]+ Terminated back_func </code></pre> <h3>More than one variables</h3> <p>For having many vars, there could by a nice manner:</p> <pre><code>$ back_func() { declare -A MYGLOBAL local vars while :; do ((MYGLOBAL["counter"]++)) IFS=\ / read -a vars &lt;&lt;&lt; "$(&lt;/proc/uptime) $(&lt;/proc/loadavg)" MYGLOBAL["uptime"]=$vars MYGLOBAL["idle"]=${vars[1]} MYGLOBAL["l01m"]=${vars[2]} MYGLOBAL["l05m"]=${vars[3]} MYGLOBAL["l15m"]=${vars[4]} MYGLOBAL["active"]=${vars[5]} MYGLOBAL["procs"]=${vars[6]} MYGLOBAL["lpid"]=${vars[7]} MYGLOBAL["rand"]=$RANDOM MYGLOBAL["crt"]=$SECONDS declare -p MYGLOBAL &gt; /dev/shm/foo sleep 1 done } </code></pre> <p>Then</p> <pre><code>$ back_func &amp; [1] 27429 $ . /dev/shm/foo $ echo ${MYGLOBAL['counter']} 5 $ echo ${MYGLOBAL['lpid']} 27432 </code></pre> <p>and from there, why not:</p> <pre><code>$ dumpMyGlobal() { . /dev/shm/foo printf "%8s " ${!MYGLOBAL[@]} echo printf "%8s " ${MYGLOBAL[@]} echo } $ dumpMyGlobal l15m uptime crt procs lpid active rand idle l05m counter l01m 0.42 13815568.06 95 554 649 1 31135 21437004.95 0.38 73 0.50 $ dumpMyGlobal l15m uptime crt procs lpid active rand idle l05m counter l01m 0.41 13815593.29 120 553 727 2 3849 21437046.41 0.35 98 0.33 </code></pre> <p>or</p> <pre><code>$ dumpMyGlobal() { . /dev/shm/foo sort &lt;( paste &lt;( printf "%-12s\n" ${!MYGLOBAL[@]} ) &lt;(printf "%s\n" ${MYGLOBAL[@]}) ) } $ dumpMyGlobal active 1 counter 297 crt 337 idle 21435798.86 l01m 0.40 l05m 0.44 l15m 0.45 lpid 30418 procs 553 rand 7328 uptime 13814820.80 </code></pre> <h3>Get variable with snapshot</h3> <p>and finally <code>getMyGlobalVar</code> function</p> <pre><code>$ declare -A MYGLOBALLOCK # snapshot variable $ getMyGlobalVar () { local i sync=false [ "$1" == "--sync" ] &amp;&amp; shift &amp;&amp; sync=true if [ -z "${MYGLOBALLOCK[*]}" ] || $sync; then . /dev/shm/foo for i in ${!MYGLOBAL[@]} do MYGLOBALLOCK[$i]=${MYGLOBAL[$i]} done fi echo ${MYGLOBALLOCK[$1]} } </code></pre> <p>will require <code>--sync</code> flag for re-reading <em>rendez-vous</em> in order to let you look about each fields from the same <em>snapshot</em>.</p> <pre><code>$ getMyGlobalVar --sync idle 362084.12 $ getMyGlobalVar idle 362084.12 $ getMyGlobalVar rand 1533 $ getMyGlobalVar rand 1533 $ getMyGlobalVar --sync rand 43256 $ getMyGlobalVar idle 362127.63 </code></pre> <h2>Full useable sample:</h2> <p>There is a full sample: <a href="http://f-hauri.ch/vrac/bash_ipc_demo.txt" rel="noreferrer">bash_ipc_demo</a></p> <p>You could use by:</p> <pre><code>wget http://f-hauri.ch/vrac/bash_ipc_demo source bash_ipc_demo back_func help Usage: bash [-q] [start|stop|restart|status|get|dump|help] back_func status Background loop function is not running. back_func start back_func status Background loop function (19939) is running. </code></pre> <p>From there, if you <code>source bash_ipc_demo</code> in another terminal, you could do the list into them.</p> <p>You could even close the first terminal.</p> <pre><code>back_func dump backFunc_count 13 backFunc_now 2016-04-06 17:03:19 backFunc_pid 19939 backFunc_running yes backFunc_start 2016-04-06 17:03:07 cpu_numcores 2 loadavg_15min 0.44 loadavg_1min 0.66 loadavg_5min 0.54 loadavg_active 1 loadavg_last_pid 20005 loadavg_process 650 random 3714432 uptime_idle 425499.43 uptime_up 495423.53 uptime_usage1sec 9.90 uptime_usage 57.06 uptime_useGraph 57.06 8.91 7.50 6.93 12.00 9.41 7.84 9.90 7.50 11.88 7.92 9.31 9.90 </code></pre> <p>Then, you could get one value</p> <pre><code>back_func get backFunc_pid newVar echo $newVar 19939 </code></pre> <p>or build a <em>last minute</em> graph:</p> <pre><code>back_func get uptime_useGraph vars;path="M0,0";x=0;for y in $vars;do printf -v step "L%.2f,%.2f L%.2f %.2f " $((x++*3)) $y $[3*x] $y path+=" $step" done;path+=" L$((3*x)),0 z";echo "&lt;svg width=\"180\" height=\"100\"&gt; &lt;rect style=\"fill: #DDD;\" width=\"180\" height=\"100\"&gt;&lt;/rect&gt; &lt;path style=\"fill: #08B;\" transform=\"matrix(1,0,0,-1,0,100)\" d=\"$path\"&gt;&lt;/path&gt;&lt;/svg&gt;" | inkscape -z --export-png=lastMinute.png /dev/stdin;eog lastMinute.png ** (inkscape:22147): WARNING **: Format autodetect failed. The file is being opened as SVG. Background RRGGBBAA: ffffff00 Area 0:0:180:100 exported to 180 x 100 pixels (90 dpi) Bitmap saved as: lastMinute.png </code></pre> <p>Then:</p> <pre><code>back_func stop back_func get backFunc_end 2016-04-06 17:16:08 </code></pre>
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