feature: add possibility to inject functions that will be called before and/or after each job

README.md

@@ -47,6 +47,10 @@ The interface consists of four public functions and one variable that reports ho
     # \brief initializes the job pool
     # \param[in] pool_size  number of parallel jobs allowed
     # \param[in] echo_command  1 to turn on echo, 0 to turn off
+    # \param[in] job_pool_function_pre_job  (optional) a function that will be called before each job
+    # \param[in] job_pool_function_post_job  (optional) a function that will be called after each job. 
+    # 
+    # To only have a post job function, the given parameter for the pre job function should be: "".
     function job_pool_init()
 
     # \brief waits for all queued up jobs to complete and shuts down the job pool
@@ -65,6 +69,8 @@ The interface consists of four public functions and one variable that reports ho
 
 This was inspired by [a discussion on StackOverflow](http://stackoverflow.com/questions/6441509/how-to-write-a-process-pool-bash-shell).
 
+For more information on the parameters "job_pool_function_pre_job" and "job_pool_function_post_job" of the "job_pool_init" function, check the sample program "job_pool_sample_injected_functions.sh".
+
 ## `genpass.sh`
 `genpass.sh` is a random password generator, it will produce a random password of the desired length which is suitable
 for manual entering via the keyboard.

job_pool.sh

@@ -45,6 +45,12 @@ job_pool_pool_size=-1
 # \brief variable to check for number of non-zero exits
 job_pool_nerrors=0
 
+# function that will be called before each job. By default, no function is called.
+job_pool_function_pre_job=""
+
+# function that will be called after each job. By default, no function is called.
+job_pool_function_post_job=""
+
 ################################################################################
 # private functions
 ################################################################################
@@ -106,6 +112,11 @@ function _job_pool_worker()
             # will know we are exiting.
             echo "${cmd}" >&7
         else
+            # run the pre job injected function if it was provided
+            if [[ "${job_pool_function_pre_job}" != "" ]]; then
+                "${job_pool_function_pre_job}"
+            fi
+
             _job_pool_echo "### _job_pool_worker-${id}: ${cmd}"
             # run the job
             { ${cmd} "$@" ; }
@@ -124,6 +135,11 @@ function _job_pool_worker()
             flock --unlock 8
             exec 8>&-
             _job_pool_echo "### _job_pool_worker-${id}: exited ${result}: ${cmd} $@"
+
+            # run the post job injected function if it was provided
+            if [[ "${job_pool_function_post_job}" != "" ]]; then
+                "${job_pool_function_post_job}"
+            fi
         fi
     done
     exec 7>&-
@@ -157,12 +173,18 @@ function _job_pool_start_workers()
 # \brief initializes the job pool
 # \param[in] pool_size  number of parallel jobs allowed
 # \param[in] echo_command  1 to turn on echo, 0 to turn off
+# \param[in] job_pool_function_pre_job  (optional) a function that will be called before each job
+# \param[in] job_pool_function_post_job  (optional) a function that will be called after each job. 
+# 
+# To only have a post job function, the given parameter for the pre job function should be: "".
 function job_pool_init()
 {
     local pool_size=$1
     local echo_command=$2
 
     # set the global attibutes
+    job_pool_function_pre_job=$3
+    job_pool_function_post_job=$4
     job_pool_pool_size=${pool_size:=1}
     job_pool_echo_command=${echo_command:=0}
 

job_pool_sample_injected_functions.sh

@@ -0,0 +1,60 @@
+#!/bin/bash
+
+. job_pool.sh
+
+#####################################################
+# Demonstration of function injection into each job #
+#####################################################
+
+echo "Demonstration of function injection into each job:"
+
+# sleep some time ($1) then echo something ($2)
+function sleep_n_echo()
+{
+    sleep "$1"
+    echo "$2"
+}
+
+# Injected function that will be called before each job
+# 
+# Print which worker is starting which job
+function print_starting_job()
+{
+    echo " # _job_pool_worker-${id}: Starting job: ${cmd} $(echo "${args[@]}" | xargs | tr '\v' ' ')"
+}
+
+# Injected function that will be called afetr each job
+# 
+# Kill all workers if the local variable "result" from _job_pool_worker
+# indicates that the job failed
+function kill_workers()
+{
+    echo " # _job_pool_worker-${id}: Finished job: ${cmd} $(echo "${args[@]}" | xargs | tr '\v' ' ')"
+
+    # result is undefined in this script, but will be defined when
+    # the function is injected in _job_pool_worker
+    if [[ "${result}" != "0" ]]; then
+        # get the pids of all workers:
+        # - each worker's process is named after the current script (here, job_pool_sample.sh),
+        #   so we use this name to get the pids
+        # - we do not include the current script's pid ($$) as it is not a worker,
+        #   (we do not want to kill the script itself, only the workers)
+        local workers_pids=("$(pgrep -f "$0" | grep -v $$)")
+        kill ${workers_pids[@]} &> /dev/null &
+    fi
+}
+
+# allow 3 parallel jobs, and kill all jobs at the first fail using "kill_workers" function
+job_pool_init 3 0 print_starting_job kill_workers
+
+# simulate 3 jobs, where one fails before the others are finished, and interrupts the others
+job_pool_run sleep_n_echo 3 a   # job 1
+job_pool_run /bin/false         # job 2
+job_pool_run sleep_n_echo 3 b   # job 3
+
+# the job 2 will kill all other running workers, using the function "kill_workers"
+# (that is ran after processing each job)
+
+job_pool_shutdown
+
+echo -e "\nOnly the failed job exited, the others did not because they were canceled."