async_hooks: use typed array stack as fast path

- Communicate the current async stack length through a
  typed array field rather than a native binding method
- Add a new fixed-size `async_ids_fast_stack` typed array
  that contains the async ID stack up to a fixed limit.
  This increases performance noticeably, since most of the time
  the async ID stack will not be more than a handful of
  levels deep.
- Make the JS `pushAsyncIds()` and `popAsyncIds()` functions
  do the same thing as the native ones if the fast path
  is applicable.

Benchmarks:

    $ ./node benchmark/compare.js --new ./node --old ./node-master --runs 10 --filter next-tick process | Rscript benchmark/compare.R
    [00:03:25|% 100| 6/6 files | 20/20 runs | 1/1 configs]: Done
                                                   improvement confidence      p.value
     process/next-tick-breadth-args.js millions=4     19.72 %        *** 3.013913e-06
     process/next-tick-breadth.js millions=4          27.33 %        *** 5.847983e-11
     process/next-tick-depth-args.js millions=12      40.08 %        *** 1.237127e-13
     process/next-tick-depth.js millions=12           77.27 %        *** 1.413290e-11
     process/next-tick-exec-args.js millions=5        13.58 %        *** 1.245180e-07
     process/next-tick-exec.js millions=5             16.80 %        *** 2.961386e-07

Backport-PR-URL: #18179
PR-URL: #17780
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/internal/async_hooks.js

@@ -19,14 +19,20 @@ const async_wrap = process.binding('async_wrap');
  *    retrieving the triggerAsyncId value is passing directly to the
  *    constructor -> value set in kDefaultTriggerAsyncId -> executionAsyncId of
  *    the current resource.
+ *
+ * async_ids_fast_stack is a Float64Array that contains part of the async ID
+ * stack. Each pushAsyncIds() call adds two doubles to it, and each
+ * popAsyncIds() call removes two doubles from it.
+ * It has a fixed size, so if that is exceeded, calls to the native
+ * side are used instead in pushAsyncIds() and popAsyncIds().
  */
 const { async_hook_fields, async_id_fields } = async_wrap;
 // Store the pair executionAsyncId and triggerAsyncId in a std::stack on
 // Environment::AsyncHooks::ids_stack_ tracks the resource responsible for the
 // current execution stack. This is unwound as each resource exits. In the case
 // of a fatal exception this stack is emptied after calling each hook's after()
 // callback.
-const { pushAsyncIds, popAsyncIds } = async_wrap;
+const { pushAsyncIds: pushAsyncIds_, popAsyncIds: popAsyncIds_ } = async_wrap;
 // For performance reasons, only track Proimses when a hook is enabled.
 const { enablePromiseHook, disablePromiseHook } = async_wrap;
 // Properties in active_hooks are used to keep track of the set of hooks being
@@ -60,8 +66,8 @@ const active_hooks = {
 // 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, kPromiseResolve,
-        kCheck, kExecutionAsyncId, kAsyncIdCounter,
-        kDefaultTriggerAsyncId } = async_wrap.constants;
+        kCheck, kExecutionAsyncId, kAsyncIdCounter, kTriggerAsyncId,
+        kDefaultTriggerAsyncId, kStackLength } = async_wrap.constants;
 
 // Used in AsyncHook and AsyncResource.
 const init_symbol = Symbol('init');
@@ -332,6 +338,38 @@ function emitDestroyScript(asyncId) {
 }
 
 
+// This is the equivalent of the native push_async_ids() call.
+function pushAsyncIds(asyncId, triggerAsyncId) {
+  const offset = async_hook_fields[kStackLength];
+  if (offset * 2 >= async_wrap.async_ids_stack.length)
+    return pushAsyncIds_(asyncId, triggerAsyncId);
+  async_wrap.async_ids_stack[offset * 2] = async_id_fields[kExecutionAsyncId];
+  async_wrap.async_ids_stack[offset * 2 + 1] = async_id_fields[kTriggerAsyncId];
+  async_hook_fields[kStackLength]++;
+  async_id_fields[kExecutionAsyncId] = asyncId;
+  async_id_fields[kTriggerAsyncId] = triggerAsyncId;
+}
+
+
+// This is the equivalent of the native pop_async_ids() call.
+function popAsyncIds(asyncId) {
+  if (async_hook_fields[kStackLength] === 0) return false;
+  const stackLength = async_hook_fields[kStackLength];
+
+  if (async_hook_fields[kCheck] > 0 &&
+      async_id_fields[kExecutionAsyncId] !== asyncId) {
+    // Do the same thing as the native code (i.e. crash hard).
+    return popAsyncIds_(asyncId);
+  }
+
+  const offset = stackLength - 1;
+  async_id_fields[kExecutionAsyncId] = async_wrap.async_ids_stack[2 * offset];
+  async_id_fields[kTriggerAsyncId] = async_wrap.async_ids_stack[2 * offset + 1];
+  async_hook_fields[kStackLength] = offset;
+  return offset > 0;
+}
+
+
 module.exports = {
   // Private API
   getHookArrays,

lib/internal/bootstrap_node.js

@@ -357,9 +357,9 @@
     // Arrays containing hook flags and ids for async_hook calls.
     const { async_hook_fields, async_id_fields } = async_wrap;
     // Internal functions needed to manipulate the stack.
-    const { clearAsyncIdStack, asyncIdStackSize } = async_wrap;
+    const { clearAsyncIdStack } = async_wrap;
     const { kAfter, kExecutionAsyncId,
-            kDefaultTriggerAsyncId } = async_wrap.constants;
+            kDefaultTriggerAsyncId, kStackLength } = async_wrap.constants;
 
     process._fatalException = function(er) {
       var caught;
@@ -395,7 +395,7 @@
           do {
             NativeModule.require('internal/async_hooks').emitAfter(
               async_id_fields[kExecutionAsyncId]);
-          } while (asyncIdStackSize() > 0);
+          } while (async_hook_fields[kStackLength] > 0);
         // Or completely empty the id stack.
         } else {
           clearAsyncIdStack();

src/aliased_buffer.h

@@ -95,6 +95,21 @@ class AliasedBuffer {
     js_array_.Reset();
   }
 
+  AliasedBuffer& operator=(AliasedBuffer&& that) {
+    this->~AliasedBuffer();
+    isolate_ = that.isolate_;
+    count_ = that.count_;
+    byte_offset_ = that.byte_offset_;
+    buffer_ = that.buffer_;
+    free_buffer_ = that.free_buffer_;
+
+    js_array_.Reset(isolate_, that.js_array_.Get(isolate_));
+
+    that.buffer_ = nullptr;
+    that.js_array_.Reset();
+    return *this;
+  }
+
   /**
    * Helper class that is returned from operator[] to support assignment into
    * a specified location.
@@ -111,11 +126,17 @@ class AliasedBuffer {
           index_(that.index_) {
     }
 
-    inline Reference& operator=(const NativeT &val) {
+    template <typename T>
+    inline Reference& operator=(const T& val) {
       aliased_buffer_->SetValue(index_, val);
       return *this;
     }
 
+    // This is not caught by the template operator= above.
+    inline Reference& operator=(const Reference& val) {
+      return *this = static_cast<NativeT>(val);
+    }
+
     operator NativeT() const {
       return aliased_buffer_->GetValue(index_);
     }
@@ -186,8 +207,12 @@ class AliasedBuffer {
     return GetValue(index);
   }
 
+  size_t Length() const {
+    return count_;
+  }
+
  private:
-  v8::Isolate* const isolate_;
+  v8::Isolate* isolate_;
   size_t count_;
   size_t byte_offset_;
   NativeT* buffer_;

src/async_wrap.cc

@@ -489,13 +489,6 @@ void AsyncWrap::PopAsyncIds(const FunctionCallbackInfo<Value>& args) {
 }
 
 
-void AsyncWrap::AsyncIdStackSize(const FunctionCallbackInfo<Value>& args) {
-  Environment* env = Environment::GetCurrent(args);
-  args.GetReturnValue().Set(
-      static_cast<double>(env->async_hooks()->stack_size()));
-}
-
-
 void AsyncWrap::ClearAsyncIdStack(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
   env->async_hooks()->clear_async_id_stack();
@@ -534,7 +527,6 @@ void AsyncWrap::Initialize(Local<Object> target,
   env->SetMethod(target, "setupHooks", SetupHooks);
   env->SetMethod(target, "pushAsyncIds", PushAsyncIds);
   env->SetMethod(target, "popAsyncIds", PopAsyncIds);
-  env->SetMethod(target, "asyncIdStackSize", AsyncIdStackSize);
   env->SetMethod(target, "clearAsyncIdStack", ClearAsyncIdStack);
   env->SetMethod(target, "queueDestroyAsyncId", QueueDestroyAsyncId);
   env->SetMethod(target, "enablePromiseHook", EnablePromiseHook);
@@ -572,6 +564,10 @@ void AsyncWrap::Initialize(Local<Object> target,
                          "async_id_fields",
                          env->async_hooks()->async_id_fields().GetJSArray());
 
+  target->Set(context,
+              env->async_ids_stack_string(),
+              env->async_hooks()->async_ids_stack().GetJSArray()).FromJust();
+
   Local<Object> constants = Object::New(isolate);
 #define SET_HOOKS_CONSTANT(name)                                              \
   FORCE_SET_TARGET_FIELD(                                                     \
@@ -588,6 +584,7 @@ void AsyncWrap::Initialize(Local<Object> target,
   SET_HOOKS_CONSTANT(kTriggerAsyncId);
   SET_HOOKS_CONSTANT(kAsyncIdCounter);
   SET_HOOKS_CONSTANT(kDefaultTriggerAsyncId);
+  SET_HOOKS_CONSTANT(kStackLength);
 #undef SET_HOOKS_CONSTANT
   FORCE_SET_TARGET_FIELD(target, "constants", constants);
 
@@ -617,6 +614,7 @@ void AsyncWrap::Initialize(Local<Object> target,
   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>());
+  env->set_async_hooks_binding(target);
 }
 
 

src/async_wrap.h

@@ -123,7 +123,6 @@ class AsyncWrap : public BaseObject {
   static void GetAsyncId(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void PushAsyncIds(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void PopAsyncIds(const v8::FunctionCallbackInfo<v8::Value>& args);
-  static void AsyncIdStackSize(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void ClearAsyncIdStack(
     const v8::FunctionCallbackInfo<v8::Value>& args);
   static void AsyncReset(const v8::FunctionCallbackInfo<v8::Value>& args);

src/env-inl.h

@@ -81,11 +81,11 @@ inline uint32_t* IsolateData::zero_fill_field() const {
   return zero_fill_field_;
 }
 
-inline Environment::AsyncHooks::AsyncHooks(v8::Isolate* isolate)
-    : isolate_(isolate),
-      fields_(isolate, kFieldsCount),
-      async_id_fields_(isolate, kUidFieldsCount) {
-  v8::HandleScope handle_scope(isolate_);
+inline Environment::AsyncHooks::AsyncHooks()
+    : async_ids_stack_(env()->isolate(), 16 * 2),
+      fields_(env()->isolate(), kFieldsCount),
+      async_id_fields_(env()->isolate(), kUidFieldsCount) {
+  v8::HandleScope handle_scope(env()->isolate());
 
   // kDefaultTriggerAsyncId should be -1, this indicates that there is no
   // specified default value and it should fallback to the executionAsyncId.
@@ -102,9 +102,9 @@ inline Environment::AsyncHooks::AsyncHooks(v8::Isolate* isolate)
   // strings can be retrieved quickly.
 #define V(Provider)                                                           \
   providers_[AsyncWrap::PROVIDER_ ## Provider].Set(                           \
-      isolate_,                                                               \
+      env()->isolate(),                                                       \
       v8::String::NewFromOneByte(                                             \
-        isolate_,                                                             \
+        env()->isolate(),                                                     \
         reinterpret_cast<const uint8_t*>(#Provider),                          \
         v8::NewStringType::kInternalized,                                     \
         sizeof(#Provider) - 1).ToLocalChecked());
@@ -122,15 +122,25 @@ Environment::AsyncHooks::async_id_fields() {
   return async_id_fields_;
 }
 
+inline AliasedBuffer<double, v8::Float64Array>&
+Environment::AsyncHooks::async_ids_stack() {
+  return async_ids_stack_;
+}
+
 inline v8::Local<v8::String> Environment::AsyncHooks::provider_string(int idx) {
-  return providers_[idx].Get(isolate_);
+  return providers_[idx].Get(env()->isolate());
 }
 
 inline void Environment::AsyncHooks::force_checks() {
   // fields_ does not have the += operator defined
   fields_[kCheck] = fields_[kCheck] + 1;
 }
 
+inline Environment* Environment::AsyncHooks::env() {
+  return Environment::ForAsyncHooks(this);
+}
+
+// Remember to keep this code aligned with pushAsyncIds() in JS.
 inline void Environment::AsyncHooks::push_async_ids(double async_id,
                                               double trigger_async_id) {
   // Since async_hooks is experimental, do only perform the check
@@ -140,16 +150,21 @@ inline void Environment::AsyncHooks::push_async_ids(double async_id,
     CHECK_GE(trigger_async_id, -1);
   }
 
-  async_ids_stack_.push({ async_id_fields_[kExecutionAsyncId],
-                    async_id_fields_[kTriggerAsyncId] });
+  uint32_t offset = fields_[kStackLength];
+  if (offset * 2 >= async_ids_stack_.Length())
+    grow_async_ids_stack();
+  async_ids_stack_[2 * offset] = async_id_fields_[kExecutionAsyncId];
+  async_ids_stack_[2 * offset + 1] = async_id_fields_[kTriggerAsyncId];
+  fields_[kStackLength] = fields_[kStackLength] + 1;
   async_id_fields_[kExecutionAsyncId] = async_id;
   async_id_fields_[kTriggerAsyncId] = trigger_async_id;
 }
 
+// Remember to keep this code aligned with popAsyncIds() in JS.
 inline bool Environment::AsyncHooks::pop_async_id(double async_id) {
   // In case of an exception then this may have already been reset, if the
   // stack was multiple MakeCallback()'s deep.
-  if (async_ids_stack_.empty()) return false;
+  if (fields_[kStackLength] == 0) return false;
 
   // Ask for the async_id to be restored as a check that the stack
   // hasn't been corrupted.
@@ -161,32 +176,27 @@ inline bool Environment::AsyncHooks::pop_async_id(double async_id) {
             "actual: %.f, expected: %.f)\n",
             async_id_fields_.GetValue(kExecutionAsyncId),
             async_id);
-    Environment* env = Environment::GetCurrent(isolate_);
     DumpBacktrace(stderr);
     fflush(stderr);
-    if (!env->abort_on_uncaught_exception())
+    if (!env()->abort_on_uncaught_exception())
       exit(1);
     fprintf(stderr, "\n");
     fflush(stderr);
     ABORT_NO_BACKTRACE();
   }
 
-  auto async_ids = async_ids_stack_.top();
-  async_ids_stack_.pop();
-  async_id_fields_[kExecutionAsyncId] = async_ids.async_id;
-  async_id_fields_[kTriggerAsyncId] = async_ids.trigger_async_id;
-  return !async_ids_stack_.empty();
-}
+  uint32_t offset = fields_[kStackLength] - 1;
+  async_id_fields_[kExecutionAsyncId] = async_ids_stack_[2 * offset];
+  async_id_fields_[kTriggerAsyncId] = async_ids_stack_[2 * offset + 1];
+  fields_[kStackLength] = offset;
 
-inline size_t Environment::AsyncHooks::stack_size() {
-  return async_ids_stack_.size();
+  return fields_[kStackLength] > 0;
 }
 
 inline void Environment::AsyncHooks::clear_async_id_stack() {
-  while (!async_ids_stack_.empty())
-    async_ids_stack_.pop();
   async_id_fields_[kExecutionAsyncId] = 0;
   async_id_fields_[kTriggerAsyncId] = 0;
+  fields_[kStackLength] = 0;
 }
 
 inline Environment::AsyncHooks::DefaultTriggerAsyncIdScope
@@ -210,6 +220,11 @@ inline Environment::AsyncHooks::DefaultTriggerAsyncIdScope
 }
 
 
+Environment* Environment::ForAsyncHooks(AsyncHooks* hooks) {
+  return ContainerOf(&Environment::async_hooks_, hooks);
+}
+
+
 inline Environment::AsyncCallbackScope::AsyncCallbackScope(Environment* env)
     : env_(env) {
   env_->makecallback_cntr_++;
@@ -298,7 +313,6 @@ inline Environment::Environment(IsolateData* isolate_data,
                                 v8::Local<v8::Context> context)
     : isolate_(context->GetIsolate()),
       isolate_data_(isolate_data),
-      async_hooks_(context->GetIsolate()),
       timer_base_(uv_now(isolate_data->event_loop())),
       using_domains_(false),
       printed_error_(false),

src/env.cc

@@ -269,4 +269,21 @@ void Environment::ActivateImmediateCheck() {
   uv_idle_start(&immediate_idle_handle_, [](uv_idle_t*){ });
 }
 
+
+void Environment::AsyncHooks::grow_async_ids_stack() {
+  const uint32_t old_capacity = async_ids_stack_.Length() / 2;
+  const uint32_t new_capacity = old_capacity * 1.5;
+  AliasedBuffer<double, v8::Float64Array> new_buffer(
+      env()->isolate(), new_capacity * 2);
+
+  for (uint32_t i = 0; i < old_capacity * 2; ++i)
+    new_buffer[i] = async_ids_stack_[i];
+  async_ids_stack_ = std::move(new_buffer);
+
+  env()->async_hooks_binding()->Set(
+      env()->context(),
+      env()->async_ids_stack_string(),
+      async_ids_stack_.GetJSArray()).FromJust();
+}
+
 }  // namespace node