SICS-841: You can now use set_oneshot to remove a callback.

site_ansto/instrument/util/eventutil.tcl

@@ -74,7 +74,8 @@ scriptcallback connect exe BATCHEND ::batch::call_cleanup
 # @param hpath hdb path to a node which regularly calls this procedure.
 # @param event an event which may trigger a callback.
 # @param args is a list of arguments which will be passed to the callback.
-# @return state: -2 = fatal error, -1 = timer expired, 0 = callback triggered, 1 = waiting for event
+# @return state: -3 = callback cleared/removed by user, -2 = fatal error,
+#                -1 = timer expired, 0 = callback triggered, 1 = waiting for event
 # remaining before expiry.
 proc call_oneshot {hpath event args} {
   if [hpropexists $hpath oneshot_cb] {
@@ -119,11 +120,23 @@ proc call_oneshot {hpath event args} {
 # If timeout = 0 the callback will only be called if the trigger event occurs
 # the first time the node is polled.  If there is no trigger event then the
 # callback is simply removed.
-proc set_oneshot {hpath cb_proc event {timeout 60}} {
+# TODO Maybe. Allow registering a callback for each event on hpath.
+proc set_oneshot {hpath cb_proc event {cb_timeout 60}} {
+  set catch_status [ catch {
+    if {$cb_timeout == "clear"} {
+      hdelprop $hpath oneshot_cb
+      hsetprop $hpath oneshot_state -3
+      return
+    }
+    if {![string is integer $cb_timeout]} {
+      error "Valid values for the timeout are 'clear' or an integer"
+    }
     hsetprop $hpath oneshot_cb $cb_proc
-  hsetprop $hpath oneshot_timeout $timeout
+    hsetprop $hpath oneshot_timeout $cb_timeout
     hsetprop $hpath oneshot_start_time [hgetpropval $hpath read_time]
     hsetprop $hpath oneshot_trigger $event
     hsetprop $hpath oneshot_state 1
+  } catch_message ]
+  handle_exception ${catch_status} ${catch_message}
 }
 publish set_oneshot user