Add test for removing periodic event in periodic scheduler

Potentially a periodic event can be cancelled while this is processed.
Simulate this behavior removing the event inside the handler.
This was fixed by previous commit.

Signed-off-by: Frediano Ziglio <[email protected]>

Author: freddy77

ocaml/libs/xapi-stdext/lib/xapi-stdext-threads/scheduler_test.ml

@@ -24,6 +24,12 @@ let send event data = Event.(send event data |> sync)
 
 let receive event = Event.(receive event |> sync)
 
+let elapsed_ms cnt =
+  let elapsed_ns = Mtime_clock.count cnt |> Mtime.Span.to_uint64_ns in
+  Int64.(div elapsed_ns 1000000L |> to_int)
+
+let is_less = Alcotest.(testable (pp int)) Stdlib.( > )
+
 let test_single () =
   let finished = Event.new_channel () in
   Scheduler.add_to_queue "one" Scheduler.OneShot 0.001 (fun () ->
@@ -32,6 +38,28 @@ let test_single () =
   start_schedule () ;
   Alcotest.(check bool) "result" true (receive finished)
 
-let tests = [("test_single", `Quick, test_single)]
+let test_remove_self () =
+  let which = Event.new_channel () in
+  Scheduler.add_to_queue "self" (Scheduler.Periodic 0.001) 0.001 (fun () ->
+      (* this should remove the periodic scheduling *)
+      Scheduler.remove_from_queue "self" ;
+      (* add an operation to stop the test *)
+      Scheduler.add_to_queue "stop" Scheduler.OneShot 0.1 (fun () ->
+          send which "stop"
+      ) ;
+      send which "self"
+  ) ;
+  start_schedule () ;
+  let cnt = Mtime_clock.counter () in
+  Alcotest.(check string) "same event name" "self" (receive which) ;
+  Alcotest.(check string) "same event name" "stop" (receive which) ;
+  let elapsed_ms = elapsed_ms cnt in
+  Alcotest.check is_less "small time" 300 elapsed_ms
+
+let tests =
+  [
+    ("test_single", `Quick, test_single)
+  ; ("test_remove_self", `Quick, test_remove_self)
+  ]
 
 let () = Alcotest.run "Scheduler" [("generic", tests)]