Begin X4 prototype

[khatus.git] / x4 / bin / khatus_x4_lib_common_sensor.sh

diff --git a/x4/bin/khatus_x4_lib_common_sensor.sh b/x4/bin/khatus_x4_lib_common_sensor.sh
new file mode 100755 (executable)
index 0000000..fae1356
--- /dev/null
+++ b/x4/bin/khatus_x4_lib_common_sensor.sh
@@ -0,0 +1,122 @@
+#! /bin/bash
+
+set -e
+
+# Defaults
+prefix='/dev/shm/khatus'
+host="$(hostname)"
+sensor="$(basename $0)"
+run_in='foreground'  # foreground | background
+run_as='poller'      # poller | streamer
+interval=1           # Only relevant if run_as poller, ignored otherwise.
+
+set_common_options() {
+    while :
+    do
+        case "$1"
+        in '')
+            break
+        ;; -d|--daemon)
+            run_in='background'
+            shift 1
+        ;; -i|--interval)
+            case "$2"
+            in '')
+                printf "Option $1 requires and argument\n" >&2
+                exit 1
+            ;; *)
+                interval="$2"
+                shift 2
+            esac
+        ;; *)
+            shift 1
+        esac
+    done
+}
+
+init_dirs() {
+    work_dir="${prefix}/${host}/${sensor}"
+    out_dir="${work_dir}/out"
+    err_file="${work_dir}/err"
+    pid_file="${work_dir}/pid"
+
+    mkdir -p "$out_dir"
+}
+
+streamer() {
+    sensor \
+    | while read key val
+        do
+            printf "%s\n" "$val" > "${out_dir}/${key}"
+        done
+    >> "$err_file"
+}
+
+poller() {
+    while :
+    do
+        streamer
+        sleep "$interval"
+    done
+}
+
+pid_file_create_of_parent() {
+    printf "$$\n" > "$pid_file"
+}
+
+pid_file_create_of_child() {
+    printf "$!\n" > "$pid_file"
+}
+
+pid_file_test() {
+    if test -e "$pid_file"
+    then
+        printf "Error - $sensor already running (i.e. PID file exists at $pid_file)\n" 1>&2
+        exit 1
+    fi
+}
+
+pid_file_remove() {
+    rm -f "$pid_file"
+}
+
+run_in_foreground() {
+    # TODO: Why do INT and EXIT traps only work in combination?
+    trap true INT
+    trap exit TERM
+    trap pid_file_remove EXIT
+    $run_as
+}
+
+run_in_background_2nd_fork() {
+    run_in_foreground &
+    pid_file_create_of_child
+}
+
+run_in_background() {
+    run_in_background_2nd_fork &
+}
+
+run() {
+    case "$run_as"
+    in 'poller' | 'streamer')
+        true
+    ;; *)
+        printf "Error - illegal value for \$run_as: $run_in\n" 1>&2
+        exit 1
+    esac
+    pid_file_test
+    case "$run_in"
+    in 'background')
+        run_in_background
+    ;; 'foreground')
+        pid_file_create_of_parent
+        run_in_foreground
+    ;; *)
+        printf "Error - illegal value for \$run_in: $run_in\n" 1>&2
+        exit 1
+    esac
+}
+
+set_common_options $@
+init_dirs