introduce AsyncResource class

This commit adds support for the AsyncResource API to allow native
modules to asynchronously call back into JavaScript while preserving
node's async context. This acts as a higher level alternative to the
MakeCallback API. This is analogous to the AsyncResource JavaScript
class exposed by [async_hooks][] and similar to the `napi_async_init`,
`napi_async_destroy` and `napi_make_callback` APIs, albeit wrapped in
a convenient RAII form-factor.

Ref: nodejs/node#13254
[N-API]: https://nodejs.org/dist/latest-v9.x/docs/api/n-api.html#n_api_custom_asynchronous_operations
[async_hooks]: https://nodejs.org/api/async_hooks.html

Makefile

@@ -35,6 +35,7 @@ LINT_SOURCES = \
 	nan_weak.h \
 	test/cpp/accessors.cpp \
 	test/cpp/accessors2.cpp \
+	test/cpp/asyncresource.cpp \
 	test/cpp/asyncworker.cpp \
 	test/cpp/asyncprogressworker.cpp \
 	test/cpp/asyncprogressworkerstream.cpp \

doc/node_misc.md

@@ -1,16 +1,69 @@
 ## Miscellaneous Node Helpers
 
+ - <a href="#api_nan_asyncresource"><b><code>Nan::AsyncResource</code></b></a>
  - <a href="#api_nan_make_callback"><b><code>Nan::MakeCallback()</code></b></a>
  - <a href="#api_nan_module_init"><b><code>NAN_MODULE_INIT()</code></b></a>
  - <a href="#api_nan_export"><b><code>Nan::Export()</code></b></a>
 
+<a name="api_nan_asyncresource"></a>
+### Nan::AsyncResource
+
+This class is analogous to the `AsyncResource` JavaScript class exposed by Node's [async_hooks][] API.
+
+When calling back into JavaScript asynchornously, special care must be taken to ensure that the runtime can properly track
+async hops. `Nan::AsyncResource` is a class that provides an RAII wrapper around `node::EmitAsyncInit`, `node::EmitAsyncDestroy`,
+and `node::MakeCallback`. Using this mechanism to call back into JavaScript, as opposed to `Nan::MakeCallback` or
+`v8::Function::Call` ensures that the callback is executed in the correct async context. This ensures that async mechanisms
+such as domains and [async_hooks][] function correctly.
+
+Definition:
+
+```c++
+class AsyncResource {
+ public:
+  AsyncResource(MaybeLocal<v8::Object> maybe_resource, v8::Local<v8::String> name);
+  AsyncResource(MaybeLocal<v8::Object> maybe_resource, const char* name);
+  ~AsyncResource();
+
+  v8::MaybeLocal<v8::Value> runInAsyncScope(v8::Local<v8::Object> target,
+                                            v8::Local<v8::Function> func,
+                                            int argc,
+                                            v8::Local<v8::Value>* argv,
+                                            Nan::async_context async_context);
+  v8::MaybeLocal<v8::Value> runInAsyncScope(v8::Local<v8::Object> target,
+                                            v8::Local<v8::String> symbol,
+                                            int argc,
+                                            v8::Local<v8::Value>* argv,
+                                            Nan::async_context async_context);
+  v8::MaybeLocal<v8::Value> runInAsyncScope(v8::Local<v8::Object> target,
+                                            const char* method,
+                                            int argc,
+                                            v8::Local<v8::Value>* argv,
+                                            Nan::async_context async_context);
+};
+```
+
+* `maybe_resource`: An optional object associated with the async work that will be passed to the possible [async_hooks][]
+  `init` hook.
+* `name`: Identified for the kind of resource that is being provided for diagnostics information exposed by the [async_hooks][]
+  API. This will be passed to the possible `init` hook as the `type`. To avoid name collisions with other modules we recommend
+  that the name include the name of the owning module as a prefix. For example `mysql` module could use something like
+  `mysql:batch-db-query-resource`.
+* When calling JS on behalf of this resource, one can use `runInAsyncScope`. This will ensure that the callback runs in the
+  correct async execution context.
+* `AsyncDestroy` is automatically called when an AsyncResource object is destroyed.
+
+For more details, see the Node [async_hooks][] documentation. You might also want to take a look at the documentation for the
+[N-API counterpart][napi]. For example usage, see the `asyncresource.cpp` example in the `test/cpp` directory.
 
 <a name="api_nan_make_callback"></a>
 ### Nan::MakeCallback()
 
-Wrappers around `node::MakeCallback()` providing a consistent API across all supported versions of Node.
+Wrappers around the legacy `node::MakeCallback()` APIs.
 
-Use `MakeCallback()` rather than using `v8::Function#Call()` directly in order to properly process internal Node functionality including domains, async hooks, the microtask queue, and other debugging functionality.
+We recommend that you use the `AsyncResource` class and `AsyncResource::runInAsyncScope` instead of using `Nan::MakeCallback` or
+`v8::Function#Call()` directly. `AsyncResource` properly takes care of running the callback in the correct async execution
+context – something that is essential for functionality like domains, async_hooks and async debugging.
 
 Signatures:
 
@@ -61,3 +114,6 @@ NAN_MODULE_INIT(Init) {
   NAN_EXPORT(target, Foo);
 }
 ```
+
+[async_hooks]: https://nodejs.org/dist/latest-v9.x/docs/api/async_hooks.html
+[napi]: https://nodejs.org/dist/latest-v9.x/docs/api/n-api.html#n_api_custom_asynchronous_operations

nan.h

@@ -1273,6 +1273,104 @@ class Utf8String {
 
 #endif  // NODE_MODULE_VERSION
 
+//=== async_context ============================================================
+
+#if NODE_MODULE_VERSION >= NODE_8_0_MODULE_VERSION
+  typedef node::async_context async_context;
+#else
+  struct async_context {};
+#endif
+
+// === AsyncResource ===========================================================
+
+  class AsyncResource {
+   public:
+    AsyncResource(
+        MaybeLocal<v8::Object> maybe_resource
+      , v8::Local<v8::String> resource_name) {
+#if NODE_MODULE_VERSION >= NODE_8_0_MODULE_VERSION
+      v8::Isolate* isolate = v8::Isolate::GetCurrent();
+
+      v8::Local<v8::Object> resource =
+          maybe_resource.IsEmpty() ? New<v8::Object>()
+                                  : maybe_resource.ToLocalChecked();
+
+      node::async_context context =
+          node::EmitAsyncInit(isolate, resource, resource_name);
+      asyncContext = static_cast<async_context>(context);
+#endif
+    }
+
+    AsyncResource(MaybeLocal<v8::Object> maybe_resource, const char* name) {
+#if NODE_MODULE_VERSION >= NODE_8_0_MODULE_VERSION
+      v8::Isolate* isolate = v8::Isolate::GetCurrent();
+
+      v8::Local<v8::Object> resource =
+          maybe_resource.IsEmpty() ? New<v8::Object>()
+                                  : maybe_resource.ToLocalChecked();
+      v8::Local<v8::String> name_string =
+          New<v8::String>(name).ToLocalChecked();
+      node::async_context context =
+          node::EmitAsyncInit(isolate, resource, name_string);
+      asyncContext = static_cast<async_context>(context);
+#endif
+    }
+
+    ~AsyncResource() {
+#if NODE_MODULE_VERSION >= NODE_8_0_MODULE_VERSION
+      v8::Isolate* isolate = v8::Isolate::GetCurrent();
+      node::async_context node_context =
+          static_cast<node::async_context>(asyncContext);
+      node::EmitAsyncDestroy(isolate, node_context);
+#endif
+    }
+
+    inline MaybeLocal<v8::Value> runInAsyncScope(
+        v8::Local<v8::Object> target
+      , v8::Local<v8::Function> func
+      , int argc
+      , v8::Local<v8::Value>* argv) {
+#if NODE_MODULE_VERSION < NODE_8_0_MODULE_VERSION
+      return MakeCallback(target, func, argc, argv);
+#else
+      return node::MakeCallback(
+          v8::Isolate::GetCurrent(), target, func, argc, argv,
+          static_cast<node::async_context>(asyncContext));
+#endif
+    }
+
+    inline MaybeLocal<v8::Value> runInAsyncScope(
+        v8::Local<v8::Object> target
+      , v8::Local<v8::String> symbol
+      , int argc
+      , v8::Local<v8::Value>* argv) {
+#if NODE_MODULE_VERSION < NODE_8_0_MODULE_VERSION
+      return MakeCallback(target, symbol, argc, argv);
+#else
+      return node::MakeCallback(
+          v8::Isolate::GetCurrent(), target, symbol, argc, argv,
+          static_cast<node::async_context>(asyncContext));
+#endif
+    }
+
+    inline MaybeLocal<v8::Value> runInAsyncScope(
+        v8::Local<v8::Object> target
+      , const char* method
+      , int argc
+      , v8::Local<v8::Value>* argv) {
+#if NODE_MODULE_VERSION < NODE_8_0_MODULE_VERSION
+      return MakeCallback(target, method, argc, argv);
+#else
+      return node::MakeCallback(
+          v8::Isolate::GetCurrent(), target, method, argc, argv,
+          static_cast<node::async_context>(asyncContext));
+#endif
+    }
+
+   private:
+    async_context asyncContext;
+  };
+
 typedef void (*FreeCallback)(char *data, void *hint);
 
 typedef const FunctionCallbackInfo<v8::Value>& NAN_METHOD_ARGS_TYPE;

test/binding.gyp

@@ -90,6 +90,10 @@
         "target_name" : "makecallback"
       , "sources"     : [ "cpp/makecallback.cpp" ]
     }
+    , {
+        "target_name" : "asyncresource"
+      , "sources"     : [ "cpp/asyncresource.cpp" ]
+    }
     , {
         "target_name" : "isolatedata"
       , "sources"     : [ "cpp/isolatedata.cpp" ]

test/cpp/asyncresource.cpp

@@ -0,0 +1,69 @@
+/*********************************************************************
+ * NAN - Native Abstractions for Node.js
+ *
+ * Copyright (c) 2018 NAN contributors
+ *
+ * MIT License <https://github.com/nodejs/nan/blob/master/LICENSE.md>
+ ********************************************************************/
+
+#include <nan.h>
+#include <unistd.h>
+
+using namespace Nan;  // NOLINT(build/namespaces)
+
+class DelayRequest : public AsyncResource {
+ public:
+  DelayRequest(int milliseconds_, v8::Local<v8::Function> callback_)
+    : AsyncResource(MaybeLocal<v8::Object>(), "nan:test.DelayRequest"),
+      milliseconds(milliseconds_) {
+      callback.Reset(callback_);
+      request.data = this;
+    }
+  ~DelayRequest() {
+    callback.Reset();
+  }
+
+  Persistent<v8::Function> callback;
+  uv_work_t request;
+  int milliseconds;
+};
+
+void Delay(uv_work_t* req) {
+  DelayRequest *delay_request = static_cast<DelayRequest*>(req->data);
+  sleep(delay_request->milliseconds / 1000);
+}
+
+void AfterDelay(uv_work_t* req, int status) {
+  HandleScope scope;
+
+  DelayRequest *delay_request = static_cast<DelayRequest*>(req->data);
+  v8::Local<v8::Function> callback = New(delay_request->callback);
+  v8::Local<v8::Value> argv[0] = {};
+
+  v8::Local<v8::Object> target = New<v8::Object>();
+
+  // Run the callback in the async context.
+  delay_request->runInAsyncScope(target, callback, 0, argv);
+
+  delete delay_request;
+}
+
+NAN_METHOD(Delay) {
+  int delay = To<int>(info[0]).FromJust();
+  v8::Local<v8::Function> cb = To<v8::Function>(info[1]).ToLocalChecked();
+
+  DelayRequest* delay_request = new DelayRequest(delay, cb);
+
+  uv_queue_work(
+      uv_default_loop()
+    , &delay_request->request
+    , Delay
+    , reinterpret_cast<uv_after_work_cb>(AfterDelay));
+}
+
+NAN_MODULE_INIT(Init) {
+  Set(target, New<v8::String>("delay").ToLocalChecked(),
+    GetFunction(New<v8::FunctionTemplate>(Delay)).ToLocalChecked());
+}
+
+NODE_MODULE(asyncresource, Init)

test/js/asyncresource-test.js

@@ -0,0 +1,70 @@
+/*********************************************************************
+ * NAN - Native Abstractions for Node.js
+ *
+ * Copyright (c) 2018 NAN contributors
+ *
+ * MIT License <https://github.com/nodejs/nan/blob/master/LICENSE.md>
+ ********************************************************************/
+
+try {
+  require('async_hooks');
+} catch (e) {
+  process.exit(0);
+}
+
+const test     = require('tap').test
+    , testRoot = require('path').resolve(__dirname, '..')
+    , delay = require('bindings')({ module_root: testRoot, bindings: 'asyncresource' }).delay
+    , asyncHooks = require('async_hooks');
+
+test('asyncresource', function (t) {
+  t.plan(7);
+
+  var resourceAsyncId;
+  var originalExecutionAsyncId;
+  var beforeCalled = false;
+  var afterCalled = false;
+  var destroyCalled = false;
+
+  var hooks = asyncHooks.createHook({
+    init: function(asyncId, type, triggerAsyncId, resource) {
+      if (type === 'nan:test.DelayRequest') {
+        resourceAsyncId = asyncId;
+      }
+    },
+    before: function(asyncId) {
+      if (asyncId === resourceAsyncId) {
+        beforeCalled = true;
+      }
+    },
+    after: function(asyncId) {
+      if (asyncId === resourceAsyncId) {
+        afterCalled = true;
+      }
+    },
+    destroy: function(asyncId) {
+      if (asyncId === resourceAsyncId) {
+        destroyCalled = true;
+      }
+    }
+
+  });
+  hooks.enable();
+
+  originalExecutionAsyncId = asyncHooks.executionAsyncId();
+  delay(1000, function() {
+    t.equal(asyncHooks.executionAsyncId(), resourceAsyncId,
+            'callback should have the correct execution context');
+    t.equal(asyncHooks.triggerAsyncId(), originalExecutionAsyncId,
+            'callback should have the correct trigger context');
+    t.ok(beforeCalled, 'before should have been called');
+    t.notOk(afterCalled, 'after should not have been called yet');
+    setTimeout(function() {
+      t.ok(afterCalled, 'after should have been called');
+      t.ok(destroyCalled, 'destroy should have been called');
+      t.equal(asyncHooks.triggerAsyncId(), resourceAsyncId,
+              'setTimeout should have been triggered by the async resource');
+      hooks.disable();
+    }, 1);
+  });
+});