Make sure oneshot_state = 1 while a callback is waiting for an event.

site_ansto/instrument/util/eventutil.tcl

@@ -70,6 +70,7 @@ scriptcallback connect exe BATCHEND ::batch::call_cleanup
 # This is meant to be called from the read command on an hdb node. It must be
 # called everytime the node is polled so that the oneshot callback can be
 # removed if the given event fails to occur within the allowed time.
+# NOTE: set event parameter to 'fatal_error' to signal an error and remove the callback.
 # @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.
@@ -98,13 +99,13 @@ proc call_oneshot {hpath event args} {
         hdelprop $hpath oneshot_cb
         hsetprop $hpath oneshot_state -1
         return -1
+      }
     } else {
       hsetprop $hpath oneshot_state 1
       return 1
     }
   }
 }
-}
 
 ##
 # @brief Assign a oneshot callback to which is triggered by the given event.
@@ -113,13 +114,16 @@ proc call_oneshot {hpath event args} {
 # @param cb_proc name of the callback procedure
 # @param trigger event for callback
 # @param timeout the callback is removed when the timeout expires.
+# If timeout < 0 then the callback won't timeout but you can force it to be
+# removed by calling set_oneshot again with timeout = 0.
 # If timeout = 0 the callback will only be called if the trigger event occurs
-# the first time the node is polled. If timeout < 0 then the callback will be
-# called if the trigger event occurs and then it is removed.
+# 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}} {
   hsetprop $hpath oneshot_cb $cb_proc
   hsetprop $hpath oneshot_timeout $timeout
   hsetprop $hpath oneshot_start_time [hgetpropval $hpath read_time]
   hsetprop $hpath oneshot_trigger $event
+  hsetprop $hpath oneshot_state 1
 }
 publish set_oneshot user