feat(unitproc/bktemp-count_jobs):Add count_jobs() function

- Note: GNU parallel does what the `count_jobs()` was intended to
  facilitate: control the number of jobs spawned in bash scripts.

diff --git a/unitproc/bktemp-count_jobs b/unitproc/bktemp-count_jobs
new file mode 100644 (file)
index 0000000..cf26234
--- /dev/null
+++ b/unitproc/bktemp-count_jobs
@@ -0,0 +1,82 @@
+#!/usr/bin/env bash
+
+# Note: GNU Parallel obviates the need for this script. The main
+# motivation to writing this script was to manage the number of CPU
+# threads being spawned by a list of files being feed to a while loop.
+
+# Functions
+yell() { echo "$0: $*" >&2; } # print script path and all args to stderr
+die() { yell "$*"; exit 111; } # same as yell() but non-zero exit status
+try() { "$@" || die "cannot $*"; } # runs args as command, reports args if command fails
+count_jobs() {
+    local job_count;
+    job_count="$(jobs -r | wc -l | tr -d ' ' )";
+    #yell "DEBUG:job_count:$job_count";
+    if [[ -z $job_count ]]; then job_count="0"; fi;
+    echo "$job_count";
+}; # Return number of background jobs
+test_job() {
+    #yell "DEBUG:starting test_job() with:$1";
+    # Do work on $1 file
+    if [[ -f $1 ]]; then cat "$1" 1>/dev/random 2>&1; fi; # read file
+    sleep "$(shuf -i1-10 -n1)"; # debug
+}; # Test job
+count_jobs_display_update() {
+    # Depends: various variables
+    if [[ $(( SECONDS % jobs_update_interval )) -eq $jobs_update_init_delay ]] && \
+       [[ $permit_update == "true" ]]; then
+    jobs_beg="$jobs_n";
+    jobs_run="$(count_jobs)";
+    jobs_end="$((jobs_beg - jobs_run))";
+    yell "STATUS:$jobs_beg jobs begun. $jobs_end jobs ended. $jobs_run jobs running.";
+    permit_update="false";
+    fi;
+    if [[ $(( SECONDS % jobs_update_interval )) -eq $((jobs_update_init_delay + 1)) ]]; then
+       permit_update="true";
+    fi;
+}; # periodically display updates
+
+
+# Test Code
+path_target="/tmp"; # path to dir with files to run test_job() on
+
+## Setup file list
+list_paths="$(find "$path_target" -type f 2>/dev/null)";
+
+## Perform test_job() on each file
+jobs_max=100; # adjust me (e.g. "4" on 4-core CPU)
+jobs_update_interval=5; # seconds.
+jobs_update_init_delay=1; # seconds.
+permit_update="true"; # flag to make updates happen periodically
+jobs_n=0; # loop counter
+jobs_check_delay=0.001; # seconds between each job count check if running jobs > jobs_max
+while read -r line; do
+    ((jobs_n++));
+    #yell "DEBUG:jobs_n:$jobs_n"
+
+    ## Wait until job count falls below $jobs_max
+    while [[ "$(count_jobs)" -gt $jobs_max ]]; do
+       #yell "DEBUG:sleeping since $(count_jobs) > $jobs_max";
+       sleep "$jobs_check_delay";
+       count_jobs_display_update;
+    done;
+
+    ## Start new parallel job on file $line
+    test_job "$line" 1>/dev/null 2>&1 &
+
+    ## Get job status updates every $jobs_update_interval seconds
+    count_jobs_display_update;
+
+    #sleep 1; # debug
+done < <( shuf < <(echo -n "$list_paths") );
+yell "STATUS:All jobs ($jobs_n) started. $(count_jobs) jobs running.";
+
+# Detect when no outstanding jobs
+while [[ "$(count_jobs)" -gt 0 ]]; do
+    sleep 1;
+    count_jobs_display_update;
+done;
+yell "STATUS:No more jobs visible.";
+
+# Author: Steven Baltakatei Sandoval
+# License: GPLv3+