Merge pull request #67 from swan-io/prevent-future-hanging-when-circular

Prevent Futures from hanging when circular
swan-io · Feb 20, 2024 · dfe94fb · dfe94fb
2 parents 29c3396 + 8f52f4e
commit dfe94fb
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Showing 2 changed files with 12 additions and 1 deletion.
diff --git a/src/Future.ts b/src/Future.ts
@@ -101,8 +101,9 @@ export class Future<A> {
   ) {
     const resolver = (value: A) => {
       if (this._state.tag === "Pending") {
-        this._state.resolveCallbacks?.forEach((func) => func(value));
+        const resolveCallbacks = this._state.resolveCallbacks;
         this._state = { tag: "Resolved", value };
+        resolveCallbacks?.forEach((func) => func(value));
       }
     };
 

diff --git a/test/Future.test.ts b/test/Future.test.ts
@@ -419,3 +419,13 @@ test("Future isFuture", async () => {
   expect(Future.isFuture([])).toEqual(false);
   expect(Future.isFuture({})).toEqual(false);
 });
+
+test("Future doesn't hang", async () => {
+  const future = Future.make((resolve) => {
+    setTimeout(() => resolve(0), 10);
+  });
+  return future
+    .flatMap(() => Future.value(1))
+    .flatMap(() => future.flatMap(() => Future.value(2)))
+    .tap((value) => expect(value).toEqual(2));
+});