src: introduce internal C++ SetImmediate() mechanism

Backport-PR-URL: #18179
PR-URL: #17117
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: addaleax

src/env-inl.h

@@ -539,6 +539,13 @@ Environment::scheduled_immediate_count() {
   return scheduled_immediate_count_;
 }
 
+void Environment::SetImmediate(native_immediate_callback cb, void* data) {
+  native_immediate_callbacks_.push_back({ cb, data });
+  if (scheduled_immediate_count_[0] == 0)
+    ActivateImmediateCheck();
+  scheduled_immediate_count_[0] = scheduled_immediate_count_[0] + 1;
+}
+
 inline performance::performance_state* Environment::performance_state() {
   return performance_state_;
 }

src/env.cc

@@ -223,4 +223,56 @@ void Environment::EnvPromiseHook(v8::PromiseHookType type,
   }
 }
 
+void Environment::RunAndClearNativeImmediates() {
+  size_t count = native_immediate_callbacks_.size();
+  if (count > 0) {
+    std::vector<NativeImmediateCallback> list;
+    native_immediate_callbacks_.swap(list);
+    for (const auto& cb : list) {
+      cb.cb_(this, cb.data_);
+    }
+
+#ifdef DEBUG
+    CHECK_GE(scheduled_immediate_count_[0], count);
+#endif
+    scheduled_immediate_count_[0] = scheduled_immediate_count_[0] - count;
+  }
+}
+
+static bool MaybeStopImmediate(Environment* env) {
+  if (env->scheduled_immediate_count()[0] == 0) {
+    uv_check_stop(env->immediate_check_handle());
+    uv_idle_stop(env->immediate_idle_handle());
+    return true;
+  }
+  return false;
+}
+
+
+void Environment::CheckImmediate(uv_check_t* handle) {
+  Environment* env = Environment::from_immediate_check_handle(handle);
+  HandleScope scope(env->isolate());
+  Context::Scope context_scope(env->context());
+
+  if (MaybeStopImmediate(env))
+    return;
+
+  env->RunAndClearNativeImmediates();
+
+  MakeCallback(env->isolate(),
+               env->process_object(),
+               env->immediate_callback_string(),
+               0,
+               nullptr,
+               {0, 0}).ToLocalChecked();
+
+  MaybeStopImmediate(env);
+}
+
+void Environment::ActivateImmediateCheck() {
+  uv_check_start(&immediate_check_handle_, CheckImmediate);
+  // Idle handle is needed only to stop the event loop from blocking in poll.
+  uv_idle_start(&immediate_idle_handle_, [](uv_idle_t*){ });
+}
+
 }  // namespace node

src/env.h

@@ -693,6 +693,11 @@ class Environment {
   bool RemovePromiseHook(promise_hook_func fn, void* arg);
   bool EmitNapiWarning();
 
+  typedef void (*native_immediate_callback)(Environment* env, void* data);
+  inline void SetImmediate(native_immediate_callback cb, void* data);
+  // This needs to be available for the JS-land setImmediate().
+  void ActivateImmediateCheck();
+
  private:
   inline void ThrowError(v8::Local<v8::Value> (*fun)(v8::Local<v8::String>),
                          const char* errmsg);
@@ -753,6 +758,14 @@ class Environment {
   };
   std::vector<PromiseHookCallback> promise_hooks_;
 
+  struct NativeImmediateCallback {
+    native_immediate_callback cb_;
+    void* data_;
+  };
+  std::vector<NativeImmediateCallback> native_immediate_callbacks_;
+  void RunAndClearNativeImmediates();
+  static void CheckImmediate(uv_check_t* handle);
+
   static void EnvPromiseHook(v8::PromiseHookType type,
                              v8::Local<v8::Promise> promise,
                              v8::Local<v8::Value> parent);

src/node.cc

@@ -3265,40 +3265,9 @@ static void DebugEnd(const FunctionCallbackInfo<Value>& args);
 
 namespace {
 
-bool MaybeStopImmediate(Environment* env) {
-  if (env->scheduled_immediate_count()[0] == 0) {
-    uv_check_stop(env->immediate_check_handle());
-    uv_idle_stop(env->immediate_idle_handle());
-    return true;
-  }
-  return false;
-}
-
-void CheckImmediate(uv_check_t* handle) {
-  Environment* env = Environment::from_immediate_check_handle(handle);
-  HandleScope scope(env->isolate());
-  Context::Scope context_scope(env->context());
-
-  if (MaybeStopImmediate(env))
-    return;
-
-  MakeCallback(env->isolate(),
-               env->process_object(),
-               env->immediate_callback_string(),
-               0,
-               nullptr,
-               {0, 0}).ToLocalChecked();
-
-  MaybeStopImmediate(env);
-}
-
-
 void ActivateImmediateCheck(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
-  uv_check_start(env->immediate_check_handle(), CheckImmediate);
-  // Idle handle is needed only to stop the event loop from blocking in poll.
-  uv_idle_start(env->immediate_idle_handle(),
-                [](uv_idle_t*){ /* do nothing, just keep the loop running */ });
+  env->ActivateImmediateCheck();
 }