#108 resolved TCD race condition

scada-common/tcallbackdsp.lua

@@ -2,6 +2,9 @@
 -- Timer Callback Dispatcher
 --
 
+local log  = require("scada-common.log")
+local util = require("scada-common.util")
+
 local tcallbackdsp = {}
 
 local registry = {}
@@ -14,6 +17,27 @@ function tcallbackdsp.dispatch(time, f)
     registry[os.startTimer(time)] = { callback = f }
 end
 
+-- request a function to be called after the specified time, aborting any registered instances of that function reference
+---@param time number seconds
+---@param f function callback function
+function tcallbackdsp.dispatch_unique(time, f)
+    -- ignore if already registered
+    for timer, entry in pairs(registry) do
+        if entry.callback == f then
+            -- found an instance of this function reference, abort it
+            log.debug(util.c("TCD: aborting duplicate timer callback (timer: ", timer, ", function: ", f, ")"))
+
+            -- cancel event and remove from registry (even if it fires it won't call)
+---@diagnostic disable-next-line: undefined-field
+            os.cancelTimer(timer)
+            registry[timer] = nil
+        end
+    end
+
+---@diagnostic disable-next-line: undefined-field
+    registry[os.startTimer(time)] = { callback = f }
+end
+
 -- lookup a timer event and execute the callback if found
 ---@param event integer timer event timer ID
 function tcallbackdsp.handle(event)