From afbf8759e11acc1a224e42f92557f5697e4691f0 Mon Sep 17 00:00:00 2001
From: Sebastian Ullrich <sebasti@nullri.ch>
Date: Wed, 20 Mar 2024 13:47:52 +0100
Subject: [PATCH] fix: deadlock in `IO.Promise.resolve` (#3693)

---
 src/runtime/object.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/runtime/object.cpp b/src/runtime/object.cpp
index fab5b3aa32..95dd2758da 100644
--- a/src/runtime/object.cpp
+++ b/src/runtime/object.cpp
@@ -788,6 +788,7 @@ public:
     void resolve(lean_task_object * t, object * v) {
         unique_lock<mutex> lock(m_mutex);
         if (t->m_value) {
+            lock.unlock(); // `dec(v)` could lead to `deactivate_task` trying to take the lock
             dec(v);
             return;
         }