x4/bin/khatus_x4_lib_common_sensor.sh

   1 #! /bin/bash
   2
   3 set -e
   4
   5 # Defaults
   6 prefix='/dev/shm/khatus'
   7 host="$(hostname)"
   8 sensor="$(basename $0)"
   9 run_in='foreground'  # foreground | background
  10 run_as='poller'      # poller | streamer
  11 interval=1           # Only relevant if run_as poller, ignored otherwise.
  12
  13 set_common_options() {
  14     while :
  15     do
  16         case "$1"
  17         in '')
  18             break
  19         ;; -d|--daemon)
  20             run_in='background'
  21             shift 1
  22         ;; -i|--interval)
  23             case "$2"
  24             in '')
  25                 printf "Option $1 requires and argument\n" >&2
  26                 exit 1
  27             ;; *)
  28                 interval="$2"
  29                 shift 2
  30             esac
  31         ;; *)
  32             shift 1
  33         esac
  34     done
  35 }
  36
  37 init_dirs() {
  38     work_dir="${prefix}/${host}/${sensor}"
  39     out_dir="${work_dir}/out"
  40     err_file="${work_dir}/err"
  41     pid_file="${work_dir}/pid"
  42
  43     mkdir -p "$out_dir"
  44 }
  45
  46 streamer() {
  47     sensor \
  48     | while read key val
  49         do
  50             printf "%s\n" "$val" > "${out_dir}/${key}"
  51         done
  52     >> "$err_file"
  53 }
  54
  55 poller() {
  56     while :
  57     do
  58         streamer
  59         sleep "$interval"
  60     done
  61 }
  62
  63 pid_file_create_of_parent() {
  64     printf "$$\n" > "$pid_file"
  65 }
  66
  67 pid_file_create_of_child() {
  68     printf "$!\n" > "$pid_file"
  69 }
  70
  71 pid_file_test() {
  72     if test -e "$pid_file"
  73     then
  74         printf "Error - $sensor already running (i.e. PID file exists at $pid_file)\n" 1>&2
  75         exit 1
  76     fi
  77 }
  78
  79 pid_file_remove() {
  80     rm -f "$pid_file"
  81 }
  82
  83 run_in_foreground() {
  84     # TODO: Why do INT and EXIT traps only work in combination?
  85     trap true INT
  86     trap exit TERM
  87     trap pid_file_remove EXIT
  88     $run_as
  89 }
  90
  91 run_in_background_2nd_fork() {
  92     run_in_foreground &
  93     pid_file_create_of_child
  94 }
  95
  96 run_in_background() {
  97     run_in_background_2nd_fork &
  98 }
  99
 100 run() {
 101     case "$run_as"
 102     in 'poller' | 'streamer')
 103         true
 104     ;; *)
 105         printf "Error - illegal value for \$run_as: $run_in\n" 1>&2
 106         exit 1
 107     esac
 108     pid_file_test
 109     case "$run_in"
 110     in 'background')
 111         run_in_background
 112     ;; 'foreground')
 113         pid_file_create_of_parent
 114         run_in_foreground
 115     ;; *)
 116         printf "Error - illegal value for \$run_in: $run_in\n" 1>&2
 117         exit 1
 118     esac
 119 }
 120
 121 set_common_options $@
 122 init_dirs