Fix thread count timing

youknowone · youknowone · commit ff4e0bf08816 · 2026-01-18T16:26:53.000+09:00
diff --git a/crates/vm/src/stdlib/thread.rs b/crates/vm/src/stdlib/thread.rs
@@ -421,14 +421,14 @@ pub(crate) mod _thread {
                 vm.new_thread()
                     .make_spawn_func(move |vm| run_thread(func, args, vm)),
             )
-            .map(|handle| {
-                vm.state.thread_count.fetch_add(1);
-                thread_to_id(&handle)
-            })
+            .map(|handle| thread_to_id(&handle))
             .map_err(|err| vm.new_runtime_error(format!("can't start new thread: {err}")))
     }
 
     fn run_thread(func: ArgCallable, args: FuncArgs, vm: &VirtualMachine) {
+        // Increment thread count when thread actually starts executing
+        vm.state.thread_count.fetch_add(1);
+
         match func.invoke(args, vm) {
             Ok(_obj) => {}
             Err(e) if e.fast_isinstance(vm.ctx.exceptions.system_exit) => {}
@@ -1168,13 +1168,6 @@ pub(crate) mod _thread {
                     // Mark as done
                     inner_for_cleanup.lock().state = ThreadHandleState::Done;
 
-                    // Signal waiting threads that this thread is done
-                    {
-                        let (lock, cvar) = &*done_event_for_cleanup;
-                        *lock.lock() = true;
-                        cvar.notify_all();
-                    }
-
                     // Handle sentinels
                     for lock in SENTINELS.take() {
                         if lock.mu.is_locked() {
@@ -1189,8 +1182,19 @@ pub(crate) mod _thread {
                     crate::vm::thread::cleanup_current_thread_frames(vm);
 
                     vm_state.thread_count.fetch_sub(1);
+
+                    // Signal waiting threads that this thread is done
+                    // This must be LAST to ensure all cleanup is complete before join() returns
+                    {
+                        let (lock, cvar) = &*done_event_for_cleanup;
+                        *lock.lock() = true;
+                        cvar.notify_all();
+                    }
                 }
 
+                // Increment thread count when thread actually starts executing
+                vm_state.thread_count.fetch_add(1);
+
                 // Run the function
                 match func.invoke((), vm) {
                     Ok(_) => {}
@@ -1206,8 +1210,6 @@ pub(crate) mod _thread {
             }))
             .map_err(|err| vm.new_runtime_error(format!("can't start new thread: {err}")))?;
 
-        vm.state.thread_count.fetch_add(1);
-
         // Store the join handle
         handle.inner.lock().join_handle = Some(join_handle);
 
