src: add a threadsafe variant of SetImmediate()

Add a variant of `SetImmediate()` that can be called from any thread.
This allows removing the `AsyncRequest` abstraction and replaces it
with a more generic mechanism.

PR-URL: #31386
Refs: openjs-foundation/summit#240
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

Author: addaleax

src/env-inl.h

@@ -745,13 +745,15 @@ Environment::NativeImmediateQueue::Shift() {
     if (!head_)
       tail_ = nullptr;  // The queue is now empty.
   }
+  size_--;
   return ret;
 }
 
 void Environment::NativeImmediateQueue::Push(
     std::unique_ptr<Environment::NativeImmediateCallback> cb) {
   NativeImmediateCallback* prev_tail = tail_;
 
+  size_++;
   tail_ = cb.get();
   if (prev_tail != nullptr)
     prev_tail->set_next(std::move(cb));
@@ -771,6 +773,10 @@ void Environment::NativeImmediateQueue::ConcatMove(
   other.size_ = 0;
 }
 
+size_t Environment::NativeImmediateQueue::size() const {
+  return size_.load();
+}
+
 template <typename Fn>
 void Environment::CreateImmediate(Fn&& cb, bool ref) {
   auto callback = std::make_unique<NativeImmediateCallbackImpl<Fn>>(
@@ -792,6 +798,17 @@ void Environment::SetUnrefImmediate(Fn&& cb) {
   CreateImmediate(std::move(cb), false);
 }
 
+template <typename Fn>
+void Environment::SetImmediateThreadsafe(Fn&& cb) {
+  auto callback = std::make_unique<NativeImmediateCallbackImpl<Fn>>(
+      std::move(cb), false);
+  {
+    Mutex::ScopedLock lock(native_immediates_threadsafe_mutex_);
+    native_immediates_threadsafe_.Push(std::move(callback));
+  }
+  uv_async_send(&task_queues_async_);
+}
+
 Environment::NativeImmediateCallback::NativeImmediateCallback(bool refed)
   : refed_(refed) {}
 
@@ -1151,7 +1168,7 @@ void Environment::RemoveCleanupHook(void (*fn)(void*), void* arg) {
 inline void Environment::RegisterFinalizationGroupForCleanup(
     v8::Local<v8::FinalizationGroup> group) {
   cleanup_finalization_groups_.emplace_back(isolate(), group);
-  uv_async_send(&cleanup_finalization_groups_async_);
+  uv_async_send(&task_queues_async_);
 }
 
 size_t CleanupHookCallback::Hash::operator()(

src/env.cc

@@ -463,15 +463,16 @@ void Environment::InitializeLibuv(bool start_profiler_idle_notifier) {
   uv_check_init(event_loop(), &idle_check_handle_);
   uv_async_init(
       event_loop(),
-      &cleanup_finalization_groups_async_,
+      &task_queues_async_,
       [](uv_async_t* async) {
         Environment* env = ContainerOf(
-            &Environment::cleanup_finalization_groups_async_, async);
+            &Environment::task_queues_async_, async);
         env->CleanupFinalizationGroups();
+        env->RunAndClearNativeImmediates();
       });
   uv_unref(reinterpret_cast<uv_handle_t*>(&idle_prepare_handle_));
   uv_unref(reinterpret_cast<uv_handle_t*>(&idle_check_handle_));
-  uv_unref(reinterpret_cast<uv_handle_t*>(&cleanup_finalization_groups_async_));
+  uv_unref(reinterpret_cast<uv_handle_t*>(&task_queues_async_));
 
   thread_stopper()->Install(
     this, static_cast<void*>(this), [](uv_async_t* handle) {
@@ -535,7 +536,7 @@ void Environment::RegisterHandleCleanups() {
       close_and_finish,
       nullptr);
   RegisterHandleCleanup(
-      reinterpret_cast<uv_handle_t*>(&cleanup_finalization_groups_async_),
+      reinterpret_cast<uv_handle_t*>(&task_queues_async_),
       close_and_finish,
       nullptr);
 }
@@ -666,6 +667,15 @@ void Environment::RunAndClearNativeImmediates(bool only_refed) {
                               "RunAndClearNativeImmediates", this);
   size_t ref_count = 0;
 
+  // It is safe to check .size() first, because there is a causal relationship
+  // between pushes to the threadsafe and this function being called.
+  // For the common case, it's worth checking the size first before establishing
+  // a mutex lock.
+  if (native_immediates_threadsafe_.size() > 0) {
+    Mutex::ScopedLock lock(native_immediates_threadsafe_mutex_);
+    native_immediates_.ConcatMove(std::move(native_immediates_threadsafe_));
+  }
+
   NativeImmediateQueue queue;
   queue.ConcatMove(std::move(native_immediates_));
 
@@ -1087,7 +1097,7 @@ void Environment::CleanupFinalizationGroups() {
       if (try_catch.HasCaught() && !try_catch.HasTerminated())
         errors::TriggerUncaughtException(isolate(), try_catch);
       // Re-schedule the execution of the remainder of the queue.
-      uv_async_send(&cleanup_finalization_groups_async_);
+      uv_async_send(&task_queues_async_);
       return;
     }
   }

src/env.h

@@ -1196,6 +1196,9 @@ class Environment : public MemoryRetainer {
   inline void SetImmediate(Fn&& cb);
   template <typename Fn>
   inline void SetUnrefImmediate(Fn&& cb);
+  template <typename Fn>
+  // This behaves like SetImmediate() but can be called from any thread.
+  inline void SetImmediateThreadsafe(Fn&& cb);
   // This needs to be available for the JS-land setImmediate().
   void ToggleImmediateRef(bool ref);
 
@@ -1281,7 +1284,7 @@ class Environment : public MemoryRetainer {
   uv_idle_t immediate_idle_handle_;
   uv_prepare_t idle_prepare_handle_;
   uv_check_t idle_check_handle_;
-  uv_async_t cleanup_finalization_groups_async_;
+  uv_async_t task_queues_async_;
   bool profiler_idle_notifier_started_ = false;
 
   AsyncHooks async_hooks_;
@@ -1433,12 +1436,18 @@ class Environment : public MemoryRetainer {
     // 'other' afterwards.
     inline void ConcatMove(NativeImmediateQueue&& other);
 
+    // size() is atomic and may be called from any thread.
+    inline size_t size() const;
+
    private:
+    std::atomic<size_t> size_ {0};
     std::unique_ptr<NativeImmediateCallback> head_;
     NativeImmediateCallback* tail_ = nullptr;
   };
 
   NativeImmediateQueue native_immediates_;
+  Mutex native_immediates_threadsafe_mutex_;
+  NativeImmediateQueue native_immediates_threadsafe_;
 
   void RunAndClearNativeImmediates(bool only_refed = false);
   static void CheckImmediate(uv_check_t* handle);