n-api: add helper for addons to get the event loop

Add a utility functions for addons to use when they need
a reference to the current event loop.

While the libuv API is not directly part of N-API, it
provides a quite stable C API as well, and is tightly
integrated with Node itself.

As a particular use case, without access to the event loop
it is hard to do something interesting from inside a N-API
finalizer function, since calls into JS and therefore virtually
all other N-API functions are not allowed.

PR-URL: https://github.com/nodejs/node/pull/17109
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

1 files changed, 19 insertions, 9 deletions

diff --git a/src/node_api.cc b/src/node_api.cc
index ad922d9ad1..84e57d03d6 100644
--- a/src/node_api.cc
+++ b/src/node_api.cc
@@ -18,7 +18,7 @@
 #include "node_api.h"
 #include "node_internals.h"
 
-#define NAPI_VERSION  1
+#define NAPI_VERSION  2
 
 static
 napi_status napi_set_last_error(napi_env env, napi_status error_code,
@@ -28,8 +28,10 @@ static
 napi_status napi_clear_last_error(napi_env env);
 
 struct napi_env__ {
-  explicit napi_env__(v8::Isolate* _isolate): isolate(_isolate),
-      last_error() {}
+  explicit napi_env__(v8::Isolate* _isolate, uv_loop_t* _loop)
+      : isolate(_isolate),
+        last_error(),
+        loop(_loop) {}
   ~napi_env__() {
     last_exception.Reset();
     wrap_template.Reset();
@@ -43,6 +45,7 @@ struct napi_env__ {
   v8::Persistent<v8::ObjectTemplate> accessor_data_template;
   napi_extended_error_info last_error;
   int open_handle_scopes = 0;
+  uv_loop_t* loop = nullptr;
 };
 
 #define ENV_OBJECT_TEMPLATE(env, prefix, destination, field_count) \
@@ -771,7 +774,7 @@ napi_env GetEnv(v8::Local<v8::Context> context) {
   if (value->IsExternal()) {
     result = static_cast<napi_env>(value.As<v8::External>()->Value());
   } else {
-    result = new napi_env__(isolate);
+    result = new napi_env__(isolate, node::GetCurrentEventLoop(isolate));
     auto external = v8::External::New(isolate, result);
 
     // We must also stop hard if the result of assigning the env to the global
@@ -3401,15 +3404,22 @@ napi_status napi_delete_async_work(napi_env env, napi_async_work work) {
   return napi_clear_last_error(env);
 }
 
+napi_status napi_get_uv_event_loop(napi_env env, uv_loop_t** loop) {
+  CHECK_ENV(env);
+  CHECK_ARG(env, loop);
+  *loop = env->loop;
+  return napi_clear_last_error(env);
+}
+
 napi_status napi_queue_async_work(napi_env env, napi_async_work work) {
   CHECK_ENV(env);
   CHECK_ARG(env, work);
 
-  // Consider: Encapsulate the uv_loop_t into an opaque pointer parameter.
-  // Currently the environment event loop is the same as the UV default loop.
-  // Someday (if node ever supports multiple isolates), it may be better to get
-  // the loop from node::Environment::GetCurrent(env->isolate)->event_loop();
-  uv_loop_t* event_loop = uv_default_loop();
+  napi_status status;
+  uv_loop_t* event_loop = nullptr;
+  status = napi_get_uv_event_loop(env, &event_loop);
+  if (status != napi_ok)
+    return napi_set_last_error(env, status);
 
   uvimpl::Work* w = reinterpret_cast<uvimpl::Work*>(work);