src: add optional keep-alive object to SetImmediate

Adds the possibility to keep a strong persistent reference to
a JS object while a `SetImmediate()` call is in effect.

Backport-PR-URL: #18050
Backport-PR-URL: #20456
PR-URL: #17183
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>

src/env-inl.h

@@ -541,8 +541,15 @@ Environment::scheduled_immediate_count() {
   return scheduled_immediate_count_;
 }
 
-void Environment::SetImmediate(native_immediate_callback cb, void* data) {
-  native_immediate_callbacks_.push_back({ cb, data });
+void Environment::SetImmediate(native_immediate_callback cb,
+                               void* data,
+                               v8::Local<v8::Object> obj) {
+  native_immediate_callbacks_.push_back({
+    cb,
+    data,
+    std::unique_ptr<v8::Persistent<v8::Object>>(
+        obj.IsEmpty() ? nullptr : new v8::Persistent<v8::Object>(isolate_, obj))
+  });
   if (scheduled_immediate_count_[0] == 0)
     ActivateImmediateCheck();
   scheduled_immediate_count_[0] = scheduled_immediate_count_[0] + 1;

src/env.cc

@@ -224,6 +224,8 @@ void Environment::RunAndClearNativeImmediates() {
     native_immediate_callbacks_.swap(list);
     for (const auto& cb : list) {
       cb.cb_(this, cb.data_);
+      if (cb.keep_alive_)
+        cb.keep_alive_->Reset();
     }
 
 #ifdef DEBUG

src/env.h

@@ -688,7 +688,11 @@ class Environment {
   bool EmitNapiWarning();
 
   typedef void (*native_immediate_callback)(Environment* env, void* data);
-  inline void SetImmediate(native_immediate_callback cb, void* data);
+  // cb will be called as cb(env, data) on the next event loop iteration.
+  // obj will be kept alive between now and after the callback has run.
+  inline void SetImmediate(native_immediate_callback cb,
+                           void* data,
+                           v8::Local<v8::Object> obj = v8::Local<v8::Object>());
   // This needs to be available for the JS-land setImmediate().
   void ActivateImmediateCheck();
 
@@ -756,6 +760,7 @@ class Environment {
   struct NativeImmediateCallback {
     native_immediate_callback cb_;
     void* data_;
+    std::unique_ptr<v8::Persistent<v8::Object>> keep_alive_;
   };
   std::vector<NativeImmediateCallback> native_immediate_callbacks_;
   void RunAndClearNativeImmediates();