Add helpful code comments to defer calls in sendTo and stop (#4394

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statelyai · Oct 25, 2023 · d66200e · d66200e
1 parent 6d50df4
commit d66200e
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Showing 2 changed files with 8 additions and 1 deletion.
diff --git a/packages/core/src/actions/send.ts b/packages/core/src/actions/send.ts
@@ -145,6 +145,8 @@ function executeSendTo(
     return;
   }
 
+  // this forms an outgoing events queue
+  // thanks to that the recipient actors are able to read the *updated* snapshot value of the sender
   actorContext.defer(() => {
     const { to, event } = params;
     actorContext?.system._relay(

diff --git a/packages/core/src/actions/stop.ts b/packages/core/src/actions/stop.ts
@@ -55,11 +55,16 @@ function executeStop(
   if (!actorRef) {
     return;
   }
+  // this allows us to prevent an actor from being started if it gets stopped within the same macrostep
+  // this can happen, for example, when the invoking state is being exited immediately by an always transition
   if (actorRef.status !== ActorStatus.Running) {
     actorContext.stopChild(actorRef);
     return;
   }
-  // TODO: recheck why this one has to be deferred
+  // stopping a child enqueues a stop event in the child actor's mailbox
+  // we need for all of the already enqueued events to be processed before we stop the child
+  // the parent itself might want to send some events to a child (for example from exit actions on the invoking state)
+  // and we don't want to ignore those events
   actorContext.defer(() => {
     actorContext.stopChild(actorRef);
   });