async_hooks: support promise resolve hook

Add a `promiseResolve()` hook.

PR-URL: #15296
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/async_hooks.md

@@ -36,7 +36,8 @@ const eid = async_hooks.executionAsyncId();
 const tid = async_hooks.triggerAsyncId();
 
 // Create a new AsyncHook instance. All of these callbacks are optional.
-const asyncHook = async_hooks.createHook({ init, before, after, destroy });
+const asyncHook =
+    async_hooks.createHook({ init, before, after, destroy, promiseResolve });
 
 // Allow callbacks of this AsyncHook instance to call. This is not an implicit
 // action after running the constructor, and must be explicitly run to begin
@@ -65,6 +66,11 @@ function after(asyncId) { }
 
 // destroy is called when an AsyncWrap instance is destroyed.
 function destroy(asyncId) { }
+
+// promiseResolve is called only for promise resources, when the
+// `resolve` function passed to the `Promise` constructor is invoked
+// (either directly or through other means of resolving a promise).
+function promiseResolve(asyncId) { }
 ```
 
 #### `async_hooks.createHook(callbacks)`
@@ -430,6 +436,36 @@ reference is made to the `resource` object passed to `init` it is possible that
 the resource does not depend on garbage collection, then this will not be an
 issue.
 
+##### `promiseResolve(asyncId)`
+
+* `asyncId` {number}
+
+Called when the `resolve` function passed to the `Promise` constructor is
+invoked (either directly or through other means of resolving a promise).
+
+Note that `resolve()` does not do any observable synchronous work.
+
+*Note:* This does not necessarily mean that the `Promise` is fulfilled or
+rejected at this point, if the `Promise` was resolved by assuming the state
+of another `Promise`.
+
+For example:
+
+```js
+new Promise((resolve) => resolve(true)).then((a) => {});
+```
+
+calls the following callbacks:
+
+```
+init for PROMISE with id 5, trigger id: 1
+  promise resolve 5      # corresponds to resolve(true)
+init for PROMISE with id 6, trigger id: 5  # the Promise returned by then()
+  before 6               # the then() callback is entered
+  promise resolve 6      # the then() callback resolves the promise by returning
+  after 6
+```
+
 #### `async_hooks.executionAsyncId()`
 
 * Returns {number} the `asyncId` of the current execution context. Useful to

lib/async_hooks.js

@@ -59,8 +59,8 @@ const active_hooks = {
 // Each constant tracks how many callbacks there are for any given step of
 // async execution. These are tracked so if the user didn't include callbacks
 // for a given step, that step can bail out early.
-const { kInit, kBefore, kAfter, kDestroy, kTotals, kCurrentAsyncId,
-        kCurrentTriggerId, kAsyncUidCntr,
+const { kInit, kBefore, kAfter, kDestroy, kPromiseResolve, kTotals,
+        kCurrentAsyncId, kCurrentTriggerId, kAsyncUidCntr,
         kInitTriggerId } = async_wrap.constants;
 
 // Symbols used to store the respective ids on both AsyncResource instances and
@@ -73,9 +73,12 @@ const init_symbol = Symbol('init');
 const before_symbol = Symbol('before');
 const after_symbol = Symbol('after');
 const destroy_symbol = Symbol('destroy');
+const promise_resolve_symbol = Symbol('promiseResolve');
 const emitBeforeNative = emitHookFactory(before_symbol, 'emitBeforeNative');
 const emitAfterNative = emitHookFactory(after_symbol, 'emitAfterNative');
 const emitDestroyNative = emitHookFactory(destroy_symbol, 'emitDestroyNative');
+const emitPromiseResolveNative =
+    emitHookFactory(promise_resolve_symbol, 'emitPromiseResolveNative');
 
 // TODO(refack): move to node-config.cc
 const abort_regex = /^--abort[_-]on[_-]uncaught[_-]exception$/;
@@ -87,7 +90,8 @@ const abort_regex = /^--abort[_-]on[_-]uncaught[_-]exception$/;
 async_wrap.setupHooks({ init: emitInitNative,
                         before: emitBeforeNative,
                         after: emitAfterNative,
-                        destroy: emitDestroyNative });
+                        destroy: emitDestroyNative,
+                        promise_resolve: emitPromiseResolveNative });
 
 // Used to fatally abort the process if a callback throws.
 function fatalError(e) {
@@ -108,7 +112,7 @@ function fatalError(e) {
 // Public API //
 
 class AsyncHook {
-  constructor({ init, before, after, destroy }) {
+  constructor({ init, before, after, destroy, promiseResolve }) {
     if (init !== undefined && typeof init !== 'function')
       throw new errors.TypeError('ERR_ASYNC_CALLBACK', 'init');
     if (before !== undefined && typeof before !== 'function')
@@ -117,11 +121,14 @@ class AsyncHook {
       throw new errors.TypeError('ERR_ASYNC_CALLBACK', 'before');
     if (destroy !== undefined && typeof destroy !== 'function')
       throw new errors.TypeError('ERR_ASYNC_CALLBACK', 'before');
+    if (promiseResolve !== undefined && typeof promiseResolve !== 'function')
+      throw new errors.TypeError('ERR_ASYNC_CALLBACK', 'promiseResolve');
 
     this[init_symbol] = init;
     this[before_symbol] = before;
     this[after_symbol] = after;
     this[destroy_symbol] = destroy;
+    this[promise_resolve_symbol] = promiseResolve;
   }
 
   enable() {
@@ -145,6 +152,8 @@ class AsyncHook {
     hook_fields[kTotals] += hook_fields[kBefore] += +!!this[before_symbol];
     hook_fields[kTotals] += hook_fields[kAfter] += +!!this[after_symbol];
     hook_fields[kTotals] += hook_fields[kDestroy] += +!!this[destroy_symbol];
+    hook_fields[kTotals] +=
+        hook_fields[kPromiseResolve] += +!!this[promise_resolve_symbol];
     hooks_array.push(this);
 
     if (prev_kTotals === 0 && hook_fields[kTotals] > 0)
@@ -167,6 +176,8 @@ class AsyncHook {
     hook_fields[kTotals] += hook_fields[kBefore] -= +!!this[before_symbol];
     hook_fields[kTotals] += hook_fields[kAfter] -= +!!this[after_symbol];
     hook_fields[kTotals] += hook_fields[kDestroy] -= +!!this[destroy_symbol];
+    hook_fields[kTotals] +=
+        hook_fields[kPromiseResolve] -= +!!this[promise_resolve_symbol];
     hooks_array.splice(index, 1);
 
     if (prev_kTotals > 0 && hook_fields[kTotals] === 0)
@@ -199,6 +210,7 @@ function storeActiveHooks() {
   active_hooks.tmp_fields[kBefore] = async_hook_fields[kBefore];
   active_hooks.tmp_fields[kAfter] = async_hook_fields[kAfter];
   active_hooks.tmp_fields[kDestroy] = async_hook_fields[kDestroy];
+  active_hooks.tmp_fields[kPromiseResolve] = async_hook_fields[kPromiseResolve];
 }
 
 
@@ -210,6 +222,7 @@ function restoreActiveHooks() {
   async_hook_fields[kBefore] = active_hooks.tmp_fields[kBefore];
   async_hook_fields[kAfter] = active_hooks.tmp_fields[kAfter];
   async_hook_fields[kDestroy] = active_hooks.tmp_fields[kDestroy];
+  async_hook_fields[kPromiseResolve] = active_hooks.tmp_fields[kPromiseResolve];
 
   active_hooks.tmp_array = null;
   active_hooks.tmp_fields = null;

src/async-wrap.cc

@@ -181,6 +181,25 @@ static void PushBackDestroyId(Environment* env, double id) {
 }
 
 
+void AsyncWrap::EmitPromiseResolve(Environment* env, double async_id) {
+  AsyncHooks* async_hooks = env->async_hooks();
+
+  if (async_hooks->fields()[AsyncHooks::kPromiseResolve] == 0)
+    return;
+
+  Local<Value> uid = Number::New(env->isolate(), async_id);
+  Local<Function> fn = env->async_hooks_promise_resolve_function();
+  TryCatch try_catch(env->isolate());
+  MaybeLocal<Value> ar = fn->Call(
+      env->context(), Undefined(env->isolate()), 1, &uid);
+  if (ar.IsEmpty()) {
+    ClearFatalExceptionHandlers(env);
+    FatalException(env->isolate(), try_catch);
+    UNREACHABLE();
+  }
+}
+
+
 void AsyncWrap::EmitBefore(Environment* env, double async_id) {
   AsyncHooks* async_hooks = env->async_hooks();
 
@@ -303,8 +322,6 @@ static void PromiseHook(PromiseHookType type, Local<Promise> promise,
     }
 
     wrap = PromiseWrap::New(env, promise, parent_wrap, silent);
-  } else if (type == PromiseHookType::kResolve) {
-    // TODO(matthewloring): need to expose this through the async hooks api.
   }
 
   CHECK_NE(wrap, nullptr);
@@ -321,6 +338,8 @@ static void PromiseHook(PromiseHookType type, Local<Promise> promise,
       // PromiseHookType::kBefore that was not witnessed by the PromiseHook.
       env->async_hooks()->pop_ids(wrap->get_id());
     }
+  } else if (type == PromiseHookType::kResolve) {
+    AsyncWrap::EmitPromiseResolve(wrap->env(), wrap->get_id());
   }
 }
 
@@ -349,6 +368,7 @@ static void SetupHooks(const FunctionCallbackInfo<Value>& args) {
   SET_HOOK_FN(before);
   SET_HOOK_FN(after);
   SET_HOOK_FN(destroy);
+  SET_HOOK_FN(promise_resolve);
 #undef SET_HOOK_FN
 
   {
@@ -500,6 +520,7 @@ void AsyncWrap::Initialize(Local<Object> target,
   SET_HOOKS_CONSTANT(kBefore);
   SET_HOOKS_CONSTANT(kAfter);
   SET_HOOKS_CONSTANT(kDestroy);
+  SET_HOOKS_CONSTANT(kPromiseResolve);
   SET_HOOKS_CONSTANT(kTotals);
   SET_HOOKS_CONSTANT(kCurrentAsyncId);
   SET_HOOKS_CONSTANT(kCurrentTriggerId);
@@ -533,6 +554,7 @@ void AsyncWrap::Initialize(Local<Object> target,
   env->set_async_hooks_before_function(Local<Function>());
   env->set_async_hooks_after_function(Local<Function>());
   env->set_async_hooks_destroy_function(Local<Function>());
+  env->set_async_hooks_promise_resolve_function(Local<Function>());
 }
 
 

src/async-wrap.h

@@ -124,6 +124,7 @@ class AsyncWrap : public BaseObject {
 
   static void EmitBefore(Environment* env, double id);
   static void EmitAfter(Environment* env, double id);
+  static void EmitPromiseResolve(Environment* env, double id);
 
   inline ProviderType provider_type() const;
 

src/env.h

@@ -296,6 +296,7 @@ struct performance_state;
   V(async_hooks_init_function, v8::Function)                                  \
   V(async_hooks_before_function, v8::Function)                                \
   V(async_hooks_after_function, v8::Function)                                 \
+  V(async_hooks_promise_resolve_function, v8::Function)                       \
   V(binding_cache_object, v8::Object)                                         \
   V(buffer_prototype_object, v8::Object)                                      \
   V(context, v8::Context)                                                     \
@@ -378,6 +379,7 @@ class Environment {
       kBefore,
       kAfter,
       kDestroy,
+      kPromiseResolve,
       kTotals,
       kFieldsCount,
     };

test/parallel/test-async-hooks-promise.js

@@ -4,11 +4,16 @@ const assert = require('assert');
 const async_hooks = require('async_hooks');
 
 const initCalls = [];
+const resolveCalls = [];
 
 async_hooks.createHook({
   init: common.mustCall((id, type, triggerId, resource) => {
     assert.strictEqual(type, 'PROMISE');
     initCalls.push({ id, triggerId, resource });
+  }, 2),
+  promiseResolve: common.mustCall((id) => {
+    assert.strictEqual(initCalls[resolveCalls.length].id, id);
+    resolveCalls.push(id);
   }, 2)
 }).enable();