x4/bin/khatus_x4_lib_common_sensor.sh

   1 #! /bin/bash
   2
   3 set -e
   4
   5 # =============================================================================
   6 # Private
   7 # =============================================================================
   8
   9 # Defaults
  10 prefix='/dev/shm/khatus'
  11 host="$(hostname)"
  12 sensor="$(basename $0)"
  13 run_in='foreground'  # foreground | background
  14 run_as='poller'      # poller | streamer
  15 interval=1           # Only relevant if run_as poller, ignored otherwise.
  16
  17 set_common_options() {
  18     while :
  19     do
  20         case "$1"
  21         in '')
  22             break
  23         ;; -d|--daemon)
  24             run_in='background'
  25             shift 1
  26         ;; -i|--interval)
  27             case "$2"
  28             in '')
  29                 printf "Option $1 requires and argument\n" >&2
  30                 exit 1
  31             ;; *)
  32                 interval="$2"
  33                 shift 2
  34             esac
  35         ;; *)
  36             shift 1
  37         esac
  38     done
  39 }
  40
  41 init_dirs() {
  42     work_dir="${prefix}/${host}/${sensor}"
  43     out_dir="${work_dir}/out"
  44     err_file="${work_dir}/err"
  45     pid_file="${work_dir}/pid"
  46
  47     mkdir -p "$out_dir"
  48 }
  49
  50 streamer() {
  51     sensor \
  52     | while read key val
  53         do
  54             printf "%s\n" "$val" > "${out_dir}/${key}"
  55         done
  56     >> "$err_file"
  57 }
  58
  59 poller() {
  60     while :
  61     do
  62         streamer
  63         sleep "$interval"
  64     done
  65 }
  66
  67 pid_file_create_of_parent() {
  68     printf "$$\n" > "$pid_file"
  69 }
  70
  71 pid_file_create_of_child() {
  72     printf "$!\n" > "$pid_file"
  73 }
  74
  75 pid_file_test() {
  76     if test -e "$pid_file"
  77     then
  78         printf "Error - $sensor already running (i.e. PID file exists at $pid_file)\n" 1>&2
  79         exit 1
  80     fi
  81 }
  82
  83 pid_file_remove() {
  84     rm -f "$pid_file"
  85 }
  86
  87 run_in_foreground() {
  88     # TODO: Why do INT and EXIT traps only work in combination?
  89     trap true INT
  90     trap exit TERM
  91     trap pid_file_remove EXIT
  92     $1
  93 }
  94
  95 run_in_background_2nd_fork() {
  96     run_in_foreground $1 &
  97     pid_file_create_of_child
  98 }
  99
 100 run_in_background() {
 101     run_in_background_2nd_fork $1 &
 102 }
 103
 104 run() {
 105     case "$run_as"
 106     in 'poller' | 'streamer')
 107         true
 108     ;; *)
 109         printf "Error - illegal value for \$run_as: $run_in\n" 1>&2
 110         exit 1
 111     esac
 112     pid_file_test
 113     case "$run_in"
 114     in 'background')
 115         run_in_background $1
 116     ;; 'foreground')
 117         pid_file_create_of_parent
 118         run_in_foreground $1
 119     ;; *)
 120         printf "Error - illegal value for \$run_in: $run_in\n" 1>&2
 121         exit 1
 122     esac
 123 }
 124
 125 # =============================================================================
 126 # API
 127 # -----------------------------------------------------------------------------
 128 #   run_as_poller
 129 #   run_as_streamer
 130 # =============================================================================
 131
 132 run_as_poller() {
 133     run 'poller'
 134 }
 135
 136 run_as_streamer() {
 137     run 'streamer'
 138 }
 139
 140 set_common_options $@
 141 init_dirs