Databases
StackOverflow2013
Postsdbo
PObash: Are writes to named pipes atomic?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PObash: Are writes to named pipes atomic?
    primarykey
    data
    text
    <p>I'm trying to parallelize the processing of a file set using bash. I'm using named pipes for keeping number of process fixed and to gather output from the processes.</p> <p>I'm assuming that the writes to named pipe are atomic, i.e the output of different process is not mixed up. Is that a safe assumption? </p> <p>Any advice is greatly appreciated. I'm limited to using bash.</p> <p>Here's the code:</p> <pre><code>mytask() { wItem=$1 #dummy func; process workItem rt=$RANDOM st=$rt; let "rt %= 2" let "st %= 10" sleep $st return $rt } parallelizeTask() { workList=$1 threadCnt=$2 task=$3 threadSyncPipeD=$4 outputSyncPipeD=$5 ti=0 for workItem in $workList; do if [ $ti -lt $threadCnt ]; then { $task $workItem; if [ $? == 0 ]; then result="success"; else result="failure"; fi; \ echo "$result:$workItem" &gt;&amp;$outputSyncPipeD; echo "$result:$workItem" &gt;&amp;$threadSyncPipeD; } &amp; ((ti++)) continue; fi while read n; do ((ti--)) break; done &lt;&amp;$threadSyncPipeD { $task $workItem; if [ $? == 0 ]; then result="success"; else result="failure"; fi; \ echo "$result:$workItem" &gt;&amp;$outputSyncPipeD; echo "$result:$workItem" &gt;&amp;$threadSyncPipeD;} &amp; ((i++)) done wait echo "quit" &gt;&amp;$outputSyncPipeD while read n; do if [[ $n == "quit" ]]; then break; else eval $6="\${$6}\ \$n" fi done &lt;&amp;$outputSyncPipeD; } main() { if [ ! -p threadSyncPipe ]; then mkfifo threadSyncPipe fi if [ ! -p outputSyncPipe ]; then mkfifo outputSyncPipe fi exec 4&lt;&gt;threadSyncPipe exec 3&lt;&gt;outputSyncPipe gout= parallelizeTask "f1 f2 f3 f4 f5 f6" 2 mytask 3 4 gout echo "finalOutput: $gout"; for f in $gout; do echo $f done rm outputSyncPipe rm threadSyncPipe } main </code></pre> <p>I found below related post with answer to my question. I have revised the title to make it more appropriate.</p> <p><a href="https://stackoverflow.com/questions/587727/are-there-repercussions-to-having-many-processes-write-to-a-single-reader-on-a-n">Are there repercussions to having many processes write to a single reader on a named pipe in posix?</a></p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USCommunity
    1. USneon
    plurals
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. PObash: Are writes to named pipes atomic?
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PObash: Are writes to named pipes atomic?
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PObash: Are writes to named pipes atomic?
      1. This table or related slice is empty.
      1. VTUpMod
    1. COWhat are you trying to do in plain English ? Your script seems like a complicated way to do something very similar to ` echo 'f1\nf2\nf3\nf4\nf5\nf6' | wargs -n1 -P2 mytask > gout ` . Or I may be totally mistaken.
      singulars
      1. PObash: Are writes to named pipes atomic?
      1. USdamienfrancois
    2. COA note on terminology: `bash` can start multiple processes, not threads. A thread is simply an execution path that shares its memory with other threads within a single process.
      singulars
      1. PObash: Are writes to named pipes atomic?
      1. USchepner
    3. COYou test for and create `threadSyncPipe` twice; I suspect the second time you mean `outputSyncPipe`.
      singulars
      1. PObash: Are writes to named pipes atomic?
      1. USchepner
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload