async_wrap: new instances get uid

New instances of AsyncWrap are automatically assigned a unique id. The
value will be used in future commits to communicate additional
information via the async hooks.

While the largest value we can reliably communicate to JS is 2^53, even
if a new AsyncWrap is created every 100ns the uid won't reach its end
for 28.5 years.

PR-URL: https://github.com/nodejs/node/pull/3461
Reviewed-By: Fedor Indutny <fedor@indutny.com>

src/async-wrap-inl.h

@@ -17,7 +17,8 @@ inline AsyncWrap::AsyncWrap(Environment* env,
                             v8::Local<v8::Object> object,
                             ProviderType provider,
                             AsyncWrap* parent)
-    : BaseObject(env, object), bits_(static_cast<uint32_t>(provider) << 1) {
+    : BaseObject(env, object), bits_(static_cast<uint32_t>(provider) << 1),
+      uid_(env->get_async_wrap_uid()) {
   CHECK_NE(provider, PROVIDER_NONE);
   CHECK_GE(object->InternalFieldCount(), 1);
 
@@ -66,6 +67,11 @@ inline AsyncWrap::ProviderType AsyncWrap::provider_type() const {
 }
 
 
+inline int64_t AsyncWrap::get_uid() const {
+  return uid_;
+}
+
+
 inline v8::Local<v8::Value> AsyncWrap::MakeCallback(
     const v8::Local<v8::String> symbol,
     int argc,

src/async-wrap.h

@@ -55,6 +55,8 @@ class AsyncWrap : public BaseObject {
 
   inline ProviderType provider_type() const;
 
+  inline int64_t get_uid() const;
+
   // Only call these within a valid HandleScope.
   v8::Local<v8::Value> MakeCallback(const v8::Local<v8::Function> cb,
                                      int argc,
@@ -76,6 +78,7 @@ class AsyncWrap : public BaseObject {
   // expected the context object will receive a _asyncQueue object property
   // that will be used to call pre/post in MakeCallback.
   uint32_t bits_;
+  const int64_t uid_;
 };
 
 void LoadAsyncWrapperInfo(Environment* env);

src/env-inl.h

@@ -210,6 +210,7 @@ inline Environment::Environment(v8::Local<v8::Context> context,
       using_domains_(false),
       printed_error_(false),
       trace_sync_io_(false),
+      async_wrap_uid_(0),
       debugger_agent_(this),
       http_parser_buffer_(nullptr),
       context_(context->GetIsolate(), context) {
@@ -359,6 +360,10 @@ inline void Environment::set_trace_sync_io(bool value) {
   trace_sync_io_ = value;
 }
 
+inline int64_t Environment::get_async_wrap_uid() {
+  return ++async_wrap_uid_;
+}
+
 inline uint32_t* Environment::heap_statistics_buffer() const {
   CHECK_NE(heap_statistics_buffer_, nullptr);
   return heap_statistics_buffer_;

src/env.h

@@ -446,6 +446,8 @@ class Environment {
   void PrintSyncTrace() const;
   inline void set_trace_sync_io(bool value);
 
+  inline int64_t get_async_wrap_uid();
+
   bool KickNextTick();
 
   inline uint32_t* heap_statistics_buffer() const;
@@ -541,6 +543,7 @@ class Environment {
   bool using_domains_;
   bool printed_error_;
   bool trace_sync_io_;
+  int64_t async_wrap_uid_;
   debugger::Agent debugger_agent_;
 
   HandleWrapQueue handle_wrap_queue_;