inspector: track async stacks when necessary

With this change, we do async stack tracking only when explicitly
requested by the inspector client. This avoids unnecessary overhead
for clients that might not be interested in async stack traces.

PR-URL: nodejs#16308
Fixes: nodejs#16180
Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>

lib/internal/inspector_async_hook.js

@@ -55,10 +55,4 @@ function disable() {
 
 exports.setup = function() {
   inspector.registerAsyncHook(enable, disable);
-
-  if (inspector.isEnabled()) {
-    // If the inspector was already enabled via --inspect or --inspect-brk,
-    // the we need to enable the async hook immediately at startup.
-    enable();
-  }
 };

src/inspector_agent.cc

@@ -319,6 +319,14 @@ class NodeInspectorClient : public V8InspectorClient {
     return uv_hrtime() * 1.0 / NANOS_PER_MSEC;
   }
 
+  void maxAsyncCallStackDepthChanged(int depth) override {
+    if (depth == 0) {
+      env_->inspector_agent()->DisableAsyncHook();
+    } else {
+      env_->inspector_agent()->EnableAsyncHook();
+    }
+  }
+
   void contextCreated(Local<Context> context, const std::string& name) {
     std::unique_ptr<StringBuffer> name_buffer = Utf8ToStringView(name);
     v8_inspector::V8ContextInfo info(context, CONTEXT_GROUP_ID,
@@ -449,7 +457,9 @@ Agent::Agent(Environment* env) : parent_env_(env),
                                  client_(nullptr),
                                  platform_(nullptr),
                                  enabled_(false),
-                                 next_context_number_(1) {}
+                                 next_context_number_(1),
+                                 pending_enable_async_hook_(false),
+                                 pending_disable_async_hook_(false) {}
 
 // Destructor needs to be defined here in implementation file as the header
 // does not have full definition of some classes.
@@ -498,17 +508,6 @@ bool Agent::StartIoThread(bool wait_for_connect) {
   HandleScope handle_scope(isolate);
   auto context = parent_env_->context();
 
-  // Enable tracking of async stack traces
-  if (!enable_async_hook_function_.IsEmpty()) {
-    Local<Function> enable_fn = enable_async_hook_function_.Get(isolate);
-    auto result = enable_fn->Call(context, Undefined(isolate), 0, nullptr);
-    if (result.IsEmpty()) {
-      FatalError(
-        "node::InspectorAgent::StartIoThread",
-        "Cannot enable Inspector's AsyncHook, please report this.");
-    }
-  }
-
   // Send message to enable debug in workers
   Local<Object> process_object = parent_env_->process_object();
   Local<Value> emit_fn =
@@ -537,38 +536,9 @@ void Agent::Stop() {
     io_.reset();
     enabled_ = false;
   }
-
-  v8::Isolate* isolate = parent_env_->isolate();
-  HandleScope handle_scope(isolate);
-
-  // Disable tracking of async stack traces
-  if (!disable_async_hook_function_.IsEmpty()) {
-    Local<Function> disable_fn = disable_async_hook_function_.Get(isolate);
-    auto result = disable_fn->Call(parent_env_->context(),
-      Undefined(parent_env_->isolate()), 0, nullptr);
-    if (result.IsEmpty()) {
-      FatalError(
-        "node::InspectorAgent::Stop",
-        "Cannot disable Inspector's AsyncHook, please report this.");
-    }
-  }
 }
 
 void Agent::Connect(InspectorSessionDelegate* delegate) {
-  if (!enabled_) {
-    // Enable tracking of async stack traces
-    v8::Isolate* isolate = parent_env_->isolate();
-    HandleScope handle_scope(isolate);
-    auto context = parent_env_->context();
-    Local<Function> enable_fn = enable_async_hook_function_.Get(isolate);
-    auto result = enable_fn->Call(context, Undefined(isolate), 0, nullptr);
-    if (result.IsEmpty()) {
-      FatalError(
-        "node::InspectorAgent::Connect",
-        "Cannot enable Inspector's AsyncHook, please report this.");
-    }
-  }
-
   enabled_ = true;
   client_->connectFrontend(delegate);
 }
@@ -626,6 +596,50 @@ void Agent::RegisterAsyncHook(Isolate* isolate,
                               v8::Local<v8::Function> disable_function) {
   enable_async_hook_function_.Reset(isolate, enable_function);
   disable_async_hook_function_.Reset(isolate, disable_function);
+  if (pending_enable_async_hook_) {
+    CHECK(!pending_disable_async_hook_);
+    pending_enable_async_hook_ = false;
+    EnableAsyncHook();
+  } else if (pending_disable_async_hook_) {
+    CHECK(!pending_enable_async_hook_);
+    pending_disable_async_hook_ = false;
+    DisableAsyncHook();
+  }
+}
+
+void Agent::EnableAsyncHook() {
+  if (!enable_async_hook_function_.IsEmpty()) {
+    Isolate* isolate = parent_env_->isolate();
+    ToggleAsyncHook(isolate, enable_async_hook_function_.Get(isolate));
+  } else if (pending_disable_async_hook_) {
+    CHECK(!pending_enable_async_hook_);
+    pending_disable_async_hook_ = false;
+  } else {
+    pending_enable_async_hook_ = true;
+  }
+}
+
+void Agent::DisableAsyncHook() {
+  if (!disable_async_hook_function_.IsEmpty()) {
+    Isolate* isolate = parent_env_->isolate();
+    ToggleAsyncHook(isolate, disable_async_hook_function_.Get(isolate));
+  } else if (pending_enable_async_hook_) {
+    CHECK(!pending_disable_async_hook_);
+    pending_enable_async_hook_ = false;
+  } else {
+    pending_disable_async_hook_ = true;
+  }
+}
+
+void Agent::ToggleAsyncHook(Isolate* isolate, Local<Function> fn) {
+  HandleScope handle_scope(isolate);
+  auto context = parent_env_->context();
+  auto result = fn->Call(context, Undefined(isolate), 0, nullptr);
+  if (result.IsEmpty()) {
+    FatalError(
+        "node::inspector::Agent::ToggleAsyncHook",
+        "Cannot toggle Inspector's AsyncHook, please report this.");
+  }
 }
 
 void Agent::AsyncTaskScheduled(const StringView& task_name, void* task,

src/inspector_agent.h

@@ -92,7 +92,12 @@ class Agent {
   DebugOptions& options() { return debug_options_; }
   void ContextCreated(v8::Local<v8::Context> context);
 
+  void EnableAsyncHook();
+  void DisableAsyncHook();
+
  private:
+  void ToggleAsyncHook(v8::Isolate* isolate, v8::Local<v8::Function> fn);
+
   node::Environment* parent_env_;
   std::unique_ptr<NodeInspectorClient> client_;
   std::unique_ptr<InspectorIo> io_;
@@ -102,6 +107,8 @@ class Agent {
   DebugOptions debug_options_;
   int next_context_number_;
 
+  bool pending_enable_async_hook_;
+  bool pending_disable_async_hook_;
   v8::Persistent<v8::Function> enable_async_hook_function_;
   v8::Persistent<v8::Function> disable_async_hook_function_;
 };

test/sequential/sequential.status

@@ -7,6 +7,7 @@ prefix sequential
 [true] # This section applies to all platforms
 
 [$system==win32]
+test-inspector-async-call-stack       : PASS, FLAKY
 test-inspector-bindings               : PASS, FLAKY
 test-inspector-debug-end              : PASS, FLAKY
 test-inspector-stop-profile-after-done: PASS, FLAKY

test/sequential/test-inspector-async-call-stack.js

@@ -0,0 +1,79 @@
+'use strict';
+const common = require('../common');
+common.skipIfInspectorDisabled();
+common.skipIf32Bits();
+
+const assert = require('assert');
+const async_wrap = process.binding('async_wrap');
+const { kTotals } = async_wrap.constants;
+const inspector = require('inspector');
+
+const setDepth = 'Debugger.setAsyncCallStackDepth';
+
+function verifyAsyncHookDisabled(message) {
+  assert.strictEqual(async_wrap.async_hook_fields[kTotals], 0);
+}
+
+function verifyAsyncHookEnabled(message) {
+  assert.strictEqual(async_wrap.async_hook_fields[kTotals], 4);
+}
+
+// By default inspector async hooks should not have been installed.
+verifyAsyncHookDisabled('inspector async hook should be disabled at startup');
+
+const session = new inspector.Session();
+verifyAsyncHookDisabled('creating a session should not enable async hooks');
+
+session.connect();
+verifyAsyncHookDisabled('connecting a session should not enable async hooks');
+
+session.post('Debugger.enable', () => {
+  verifyAsyncHookDisabled('enabling debugger should not enable async hooks');
+
+  session.post(setDepth, { invalid: 'message' }, () => {
+    verifyAsyncHookDisabled('invalid message should not enable async hooks');
+
+    session.post(setDepth, { maxDepth: 'five' }, () => {
+      verifyAsyncHookDisabled('invalid maxDepth (string) should not enable ' +
+                              'async hooks');
+
+      session.post(setDepth, { maxDepth: NaN }, () => {
+        verifyAsyncHookDisabled('invalid maxDepth (NaN) should not enable ' +
+                                'async hooks');
+
+        session.post(setDepth, { maxDepth: 10 }, () => {
+          verifyAsyncHookEnabled('valid message should enable async hooks');
+
+          session.post(setDepth, { maxDepth: 0 }, () => {
+            verifyAsyncHookDisabled('Setting maxDepth to 0 should disable ' +
+                                    'async hooks');
+
+            runTestSet2(session);
+          });
+        });
+      });
+    });
+  });
+});
+
+function runTestSet2(session) {
+  session.post(setDepth, { maxDepth: 32 }, () => {
+    verifyAsyncHookEnabled('valid message should enable async hooks');
+
+    session.post('Debugger.disable', () => {
+      verifyAsyncHookDisabled('Debugger.disable should disable async hooks');
+
+      session.post('Debugger.enable', () => {
+        verifyAsyncHookDisabled('Enabling debugger should not enable hooks');
+
+        session.post(setDepth, { maxDepth: 64 }, () => {
+          verifyAsyncHookEnabled('valid message should enable async hooks');
+
+          session.disconnect();
+          verifyAsyncHookDisabled('Disconnecting session should disable ' +
+                                  'async hooks');
+        });
+      });
+    });
+  });
+}