From 6e282b741b657e4deab13de4b90a71cbdb6d21de Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Rub=C3=A9n=20Norte?= <rubennorte@meta.com>
Date: Mon, 16 Dec 2024 03:17:08 -0800
Subject: [PATCH] Add scheduleTask and runWorkLoop to public API (#48284)

Summary:

Changelog: [internal]

We recently prevented tasks that run via `runTask` to synchronously call `runTask` because the execution is synchronous and we can't nest tasks in the event loop (D67107664 / https://github.com/facebook/react-native/pull/48235).

This adds `scheduleTask` to schedule tasks (also within tasks) with the right expectations (the task will not run synchronously on that call but at the right time).

It also adds `runWorkLoop` so we can run scheduled tasks if they're not scheduled from an already running task.

Differential Revision: D67275518
---
 packages/react-native-fantom/src/index.js | 30 +++++++++++++++++++----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/packages/react-native-fantom/src/index.js b/packages/react-native-fantom/src/index.js
index 0c3b79f7dbcd3b..179e0d7755fcb5 100644
--- a/packages/react-native-fantom/src/index.js
+++ b/packages/react-native-fantom/src/index.js
@@ -60,6 +60,17 @@ class Root {
   // TODO: add an API to check if all surfaces were deallocated when tests are finished.
 }
 
+const DEFAULT_TASK_PRIORITY = schedulerPriorityImmediate;
+
+/**
+ * Schedules a task to run on the event loop.
+ * If the work loop is running, it will be executed according to its priority.
+ * Otherwise, it will wait in the queue until the work loop runs.
+ */
+export function scheduleTask(task: () => void | Promise<void>) {
+  nativeRuntimeScheduler.unstable_scheduleCallback(DEFAULT_TASK_PRIORITY, task);
+}
+
 let flushingQueue = false;
 
 /*
@@ -70,14 +81,23 @@ let flushingQueue = false;
 export function runTask(task: () => void | Promise<void>) {
   if (flushingQueue) {
     throw new Error(
-      'Nested runTask calls are not allowed. If you want to schedule a task from inside another task, use scheduleTask instead.',
+      'Nested `runTask` calls are not allowed. If you want to schedule a task from inside another task, use `scheduleTask` instead.',
     );
   }
 
-  nativeRuntimeScheduler.unstable_scheduleCallback(
-    schedulerPriorityImmediate,
-    task,
-  );
+  scheduleTask(task);
+  runWorkLoop();
+}
+
+/**
+ * Runs the event loop until all tasks are executed.
+ */
+export function runWorkLoop(): void {
+  if (flushingQueue) {
+    throw new Error(
+      'Cannot start the work loop because it is already running. If you want to schedule a task from inside another task, use `scheduleTask` instead.',
+    );
+  }
 
   try {
     flushingQueue = true;