feat(el): Add removeDelayedCallback

arch/eventloop_posix.c

@@ -70,6 +70,22 @@ UA_EventLoopPOSIX_addDelayedCallback(UA_EventLoop *public_el,
     UA_UNLOCK(&el->elMutex);
 }
 
+static void
+UA_EventLoopPOSIX_removeDelayedCallback(UA_EventLoop *public_el,
+                                     UA_DelayedCallback *dc) {
+    UA_EventLoopPOSIX *el = (UA_EventLoopPOSIX*)public_el;
+    UA_LOCK(&el->elMutex);
+    UA_DelayedCallback **prev = &el->delayedCallbacks;
+    while(*prev) {
+        if(*prev == dc) {
+            *prev = (*prev)->next;
+            return;
+        }
+        prev = &(*prev)->next;
+    }
+    UA_UNLOCK(&el->elMutex);
+}
+
 /* Process and then free registered delayed callbacks */
 static void
 processDelayed(UA_EventLoopPOSIX *el) {
@@ -423,6 +439,7 @@ UA_EventLoop_new_POSIX(const UA_Logger *logger) {
     el->eventLoop.modifyCyclicCallback = UA_EventLoopPOSIX_modifyCyclicCallback;
     el->eventLoop.removeCyclicCallback = UA_EventLoopPOSIX_removeCyclicCallback;
     el->eventLoop.addDelayedCallback = UA_EventLoopPOSIX_addDelayedCallback;
+    el->eventLoop.removeDelayedCallback = UA_EventLoopPOSIX_removeDelayedCallback;
 
     el->eventLoop.registerEventSource =
         (UA_StatusCode (*)(UA_EventLoop*, UA_EventSource*))

include/open62541/plugin/eventloop.h

@@ -152,12 +152,18 @@ struct UA_EventLoop {
 
     /* Delayed Callbacks
      * ~~~~~~~~~~~~~~~~~
-     * The registered delayed callbacks are executed once in each cycle of the
-     * EventLoop (between the cyclic callbacks and polling for events with a
-     * timeout). The memory for the delayed callback is freed after the
+     * Delayed callbacks are executed once by the EventLoop and then
+     * deregistered automatically. A typical use case is to delay a resource
+     * cleanup to a point where it is known that the resource has no remaining
+     * users "upwards in the call stack".
+     *
+     * The execution happens in the cycle of the EventLoop between the handling
+     * of timed cyclic callbacks and polling for (network) events. The memory
+     * for the delayed callback is NOT automatically freed after the
      * execution. */
 
     void (*addDelayedCallback)(UA_EventLoop *el, UA_DelayedCallback *dc);
+    void (*removeDelayedCallback)(UA_EventLoop *el, UA_DelayedCallback *dc);
 
     /* EventSources
      * ~~~~~~~~~~~~