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="$2"
  33                 shift 2
  34             esac
  35         ;; --)
  36             shift 1
  37             break
  38         ;; *)
  39             shift 1
  40         esac
  41     done
  42 }
  43
  44 init_dirs() {
  45     work_dir="${prefix}/${host}/${sensor}"
  46     out_dir="${work_dir}/out"
  47     err_file="${work_dir}/err"
  48     pid_file="${work_dir}/pid"
  49
  50     mkdir -p "$out_dir"
  51 }
  52
  53 streamer() {
  54     sensor \
  55     | while read key val
  56         do
  57             printf "%s\n" "$val" > "${out_dir}/${key}"
  58         done
  59     >> "$err_file"
  60 }
  61
  62 poller() {
  63     while :
  64     do
  65         streamer
  66         sleep "$interval"
  67     done
  68 }
  69
  70 pid_file_create_of_parent() {
  71     printf "$$\n" > "$pid_file"
  72 }
  73
  74 pid_file_create_of_child() {
  75     printf "$!\n" > "$pid_file"
  76 }
  77
  78 pid_file_test() {
  79     if test -e "$pid_file"
  80     then
  81         printf "Error - $sensor already running (i.e. PID file exists at $pid_file)\n" 1>&2
  82         exit 1
  83     fi
  84 }
  85
  86 pid_file_remove() {
  87     rm -f "$pid_file"
  88 }
  89
  90 run_in_foreground() {
  91     # TODO: Why do INT and EXIT traps only work in combination?
  92     trap true INT
  93     trap exit TERM
  94     trap pid_file_remove EXIT
  95     $1
  96 }
  97
  98 run_in_background_2nd_fork() {
  99     run_in_foreground $1 &
 100     pid_file_create_of_child
 101 }
 102
 103 run_in_background() {
 104     run_in_background_2nd_fork $1 &
 105 }
 106
 107 run() {
 108     case "$run_as"
 109     in 'poller' | 'streamer')
 110         true
 111     ;; *)
 112         printf "Error - illegal value for \$run_as: $run_in\n" 1>&2
 113         exit 1
 114     esac
 115     pid_file_test
 116     case "$run_in"
 117     in 'background')
 118         run_in_background $1
 119     ;; 'foreground')
 120         pid_file_create_of_parent
 121         run_in_foreground $1
 122     ;; *)
 123         printf "Error - illegal value for \$run_in: $run_in\n" 1>&2
 124         exit 1
 125     esac
 126 }
 127
 128 # =============================================================================
 129 # API
 130 # -----------------------------------------------------------------------------
 131 #   run_as_poller
 132 #   run_as_streamer
 133 # =============================================================================
 134
 135 run_as_poller() {
 136     run 'poller'
 137 }
 138
 139 run_as_streamer() {
 140     run 'streamer'
 141 }
 142
 143 set_common_options $@
 144 init_dirs