Synchronizing Completion of Concurrent Commands

 

Running concurrent commands in a script generally is done by executing processes in the background.  Numerous commands can be spawned concurrently then synchronized by waiting for some, or all, of them to complete before proceeding or terminating the parent script.

     1  #!/bin/bash

     2

     3  sleep 10 &

     4  pId1=$!

     5

     6  sleep 2 &

     7  pId2=$!

     8

     9  sleep 3 &

    10  pId3=$!

    11

    12  echo "waiting for jobs to complete"

    13  #wait ; #--wait for all jobs to complete

    14  wait $pId1 $pId2 $pId3 ; #--wait for specific jobs to complete

 

In the above script, a sequence of sleeping {10, 2, and 3} seconds are executed in sequence, each in the background.  The longest running command  (e.g. 10 seconds in this example) should take 10 seconds, the other two commands concluding earlier.

We can test the proper exection, the script completing in ~10 seconds by timing the execution as follows:

$ time ./foo

waiting for jobs to complete

 

real    0m10.008s

user    0m0.003s

sys     0m0.004s

$

bash-4.1$