inspector: implement --cpu-prof-interval

doc/api/cli.md

@@ -107,6 +107,16 @@ added: v12.0.0
 Specify the directory where the CPU profiles generated by `--cpu-prof` will
 be placed.
 
+### `--cpu-prof-interval`
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+Specify the sampling interval in microseconds for the CPU profiles generated
+by `--cpu-prof`. The default is 1000 microseconds.
+
 ### `--cpu-prof-name`
 <!-- YAML
 added: v12.0.0

doc/node.1

@@ -90,6 +90,12 @@ The directory where the CPU profiles generated by
 .Fl -cpu-prof
 will be placed.
 .
+.It Fl -cpu-prof-interval
+The sampling interval in microseconds for the CPU profiles generated by
+.Fl -cpu-prof .
+The default is
+.Sy 1000 .
+.
 .It Fl -cpu-prof-name
 File name of the V8 CPU profile generated with
 .Fl -cpu-prof

src/env-inl.h

@@ -673,6 +673,14 @@ Environment::cpu_profiler_connection() {
   return cpu_profiler_connection_.get();
 }
 
+inline void Environment::set_cpu_prof_interval(uint64_t interval) {
+  cpu_prof_interval_ = interval;
+}
+
+inline uint64_t Environment::cpu_prof_interval() const {
+  return cpu_prof_interval_;
+}
+
 inline void Environment::set_cpu_prof_name(const std::string& name) {
   cpu_prof_name_ = name;
 }

src/env.h

@@ -1143,6 +1143,9 @@ class Environment : public MemoryRetainer {
   inline void set_cpu_prof_name(const std::string& name);
   inline const std::string& cpu_prof_name() const;
 
+  inline void set_cpu_prof_interval(uint64_t interval);
+  inline uint64_t cpu_prof_interval() const;
+
   inline void set_cpu_prof_dir(const std::string& dir);
   inline const std::string& cpu_prof_dir() const;
 #endif  // HAVE_INSPECTOR
@@ -1183,6 +1186,7 @@ class Environment : public MemoryRetainer {
   std::string coverage_directory_;
   std::string cpu_prof_dir_;
   std::string cpu_prof_name_;
+  uint64_t cpu_prof_interval_;
 #endif  // HAVE_INSPECTOR
 
   std::shared_ptr<EnvironmentOptions> options_;

src/inspector_profiler.cc

@@ -1,4 +1,5 @@
 #include "inspector_profiler.h"
+#include <sstream>
 #include "base_object-inl.h"
 #include "debug_utils.h"
 #include "node_file.h"
@@ -20,7 +21,6 @@ using v8::Object;
 using v8::String;
 using v8::Value;
 
-using v8_inspector::StringBuffer;
 using v8_inspector::StringView;
 
 #ifdef _WIN32
@@ -33,21 +33,34 @@ const char* const kPathSeparator = "/";
 #define CWD_BUFSIZE (PATH_MAX)
 #endif
 
-std::unique_ptr<StringBuffer> ToProtocolString(Isolate* isolate,
-                                               Local<Value> value) {
-  TwoByteValue buffer(isolate, value);
-  return StringBuffer::create(StringView(*buffer, buffer.length()));
-}
-
 V8ProfilerConnection::V8ProfilerConnection(Environment* env)
     : session_(env->inspector_agent()->Connect(
           std::make_unique<V8ProfilerConnection::V8ProfilerSessionDelegate>(
               this),
           false)),
       env_(env) {}
 
-void V8ProfilerConnection::DispatchMessage(Local<String> message) {
-  session_->Dispatch(ToProtocolString(env()->isolate(), message)->string());
+size_t V8ProfilerConnection::DispatchMessage(const char* method,
+                                             const char* params) {
+  std::stringstream ss;
+  size_t id = next_id();
+  ss << R"({ "id": )" << id;
+  DCHECK(method != nullptr);
+  ss << R"(, "method": ")" << method << '"';
+  if (params != nullptr) {
+    ss << R"(, "params": )" << params;
+  }
+  ss << " }";
+  std::string message = ss.str();
+  const uint8_t* message_data =
+      reinterpret_cast<const uint8_t*>(message.c_str());
+  Debug(env(),
+        DebugCategory::INSPECTOR_PROFILER,
+        "Dispatching message %s\n",
+        message.c_str());
+  session_->Dispatch(StringView(message_data, message.length()));
+  // TODO(joyeecheung): use this to identify the ending message.
+  return id;
 }
 
 static void WriteResult(Environment* env,
@@ -202,34 +215,15 @@ std::string V8CoverageConnection::GetDirectory() const {
 }
 
 void V8CoverageConnection::Start() {
-  Debug(env(),
-        DebugCategory::INSPECTOR_PROFILER,
-        "Sending Profiler.startPreciseCoverage\n");
-  Isolate* isolate = env()->isolate();
-  Local<String> enable = FIXED_ONE_BYTE_STRING(
-      isolate, R"({"id": 1, "method": "Profiler.enable"})");
-  Local<String> start = FIXED_ONE_BYTE_STRING(isolate, R"({
-      "id": 2,
-      "method": "Profiler.startPreciseCoverage",
-      "params": { "callCount": true, "detailed": true }
-  })");
-  DispatchMessage(enable);
-  DispatchMessage(start);
+  DispatchMessage("Profiler.enable");
+  DispatchMessage("Profiler.startPreciseCoverage",
+                  R"({ "callCount": true, "detailed": true })");
 }
 
 void V8CoverageConnection::End() {
   CHECK_EQ(ending_, false);
   ending_ = true;
-  Debug(env(),
-        DebugCategory::INSPECTOR_PROFILER,
-        "Sending Profiler.takePreciseCoverage\n");
-  Isolate* isolate = env()->isolate();
-  HandleScope scope(isolate);
-  Local<String> end = FIXED_ONE_BYTE_STRING(isolate, R"({
-      "id": 3,
-      "method": "Profiler.takePreciseCoverage"
-  })");
-  DispatchMessage(end);
+  DispatchMessage("Profiler.takePreciseCoverage");
 }
 
 std::string V8CpuProfilerConnection::GetDirectory() const {
@@ -257,25 +251,18 @@ MaybeLocal<Object> V8CpuProfilerConnection::GetProfile(Local<Object> result) {
 }
 
 void V8CpuProfilerConnection::Start() {
-  Debug(env(), DebugCategory::INSPECTOR_PROFILER, "Sending Profiler.start\n");
-  Isolate* isolate = env()->isolate();
-  Local<String> enable = FIXED_ONE_BYTE_STRING(
-      isolate, R"({"id": 1, "method": "Profiler.enable"})");
-  Local<String> start = FIXED_ONE_BYTE_STRING(
-      isolate, R"({"id": 2, "method": "Profiler.start"})");
-  DispatchMessage(enable);
-  DispatchMessage(start);
+  DispatchMessage("Profiler.enable");
+  DispatchMessage("Profiler.start");
+  std::string params = R"({ "interval": )";
+  params += std::to_string(env()->cpu_prof_interval());
+  params += " }";
+  DispatchMessage("Profiler.setSamplingInterval", params.c_str());
 }
 
 void V8CpuProfilerConnection::End() {
   CHECK_EQ(ending_, false);
   ending_ = true;
-  Debug(env(), DebugCategory::INSPECTOR_PROFILER, "Sending Profiler.stop\n");
-  Isolate* isolate = env()->isolate();
-  HandleScope scope(isolate);
-  Local<String> end =
-      FIXED_ONE_BYTE_STRING(isolate, R"({"id": 3, "method": "Profiler.stop"})");
-  DispatchMessage(end);
+  DispatchMessage("Profiler.stop");
 }
 
 // For now, we only support coverage profiling, but we may add more
@@ -320,6 +307,7 @@ void StartProfilers(Environment* env) {
   }
   if (env->options()->cpu_prof) {
     const std::string& dir = env->options()->cpu_prof_dir;
+    env->set_cpu_prof_interval(env->options()->cpu_prof_interval);
     env->set_cpu_prof_dir(dir.empty() ? GetCwd() : dir);
     if (env->options()->cpu_prof_name.empty()) {
       DiagnosticFilename filename(env, "CPU", "cpuprofile");

src/inspector_profiler.h

@@ -34,7 +34,13 @@ class V8ProfilerConnection {
   virtual ~V8ProfilerConnection() = default;
 
   Environment* env() const { return env_; }
-  void DispatchMessage(v8::Local<v8::String> message);
+
+  // Dispatch a protocol message, and returns the id of the message.
+  // `method` does not need to be surrounded by quotes.
+  // The optional `params` should be formatted in JSON.
+  // The strings should be in one byte characters - which is enough for
+  // the commands we use here.
+  size_t DispatchMessage(const char* method, const char* params = nullptr);
 
   // Use DispatchMessage() to dispatch necessary inspector messages
   // to start and end the profiling.
@@ -55,9 +61,11 @@ class V8ProfilerConnection {
       v8::Local<v8::Object> result) = 0;
 
  private:
+  size_t next_id() { return id_++; }
   void WriteProfile(v8::Local<v8::String> message);
   std::unique_ptr<inspector::InspectorSession> session_;
   Environment* env_ = nullptr;
+  size_t id_ = 1;
 };
 
 class V8CoverageConnection : public V8ProfilerConnection {

src/node_options.cc

@@ -156,6 +156,11 @@ void EnvironmentOptions::CheckOptions(std::vector<std::string>* errors) {
     if (!cpu_prof_dir.empty()) {
       errors->push_back("--cpu-prof-dir must be used with --cpu-prof");
     }
+    // We can't catch the case where the value passed is the default value,
+    // then the option just becomes a noop which is fine.
+    if (cpu_prof_interval != kDefaultCpuProfInterval) {
+      errors->push_back("--cpu-prof-interval must be used with --cpu-prof");
+    }
   }
 
   debug_options_.CheckOptions(errors);
@@ -351,6 +356,10 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             "specified file name of the V8 CPU profile generated with "
             "--cpu-prof",
             &EnvironmentOptions::cpu_prof_name);
+  AddOption("--cpu-prof-interval",
+            "specified sampling interval in microseconds for the V8 CPU "
+            "profile generated with --cpu-prof. (default: 1000)",
+            &EnvironmentOptions::cpu_prof_interval);
   AddOption("--cpu-prof-dir",
             "Directory where the V8 profiles generated by --cpu-prof will be "
             "placed. Does not affect --prof.",

src/node_options.h

@@ -111,6 +111,8 @@ class EnvironmentOptions : public Options {
   bool prof_process = false;
 #if HAVE_INSPECTOR
   std::string cpu_prof_dir;
+  static const uint64_t kDefaultCpuProfInterval = 1000;
+  uint64_t cpu_prof_interval = kDefaultCpuProfInterval;
   std::string cpu_prof_name;
   bool cpu_prof = false;
 #endif  // HAVE_INSPECTOR

test/fixtures/workload/fibonacci-worker-argv.js

@@ -3,5 +3,9 @@
 const { Worker } = require('worker_threads');
 const path = require('path');
 new Worker(path.join(__dirname, 'fibonacci.js'), {
-  execArgv: ['--cpu-prof']
+  execArgv: [
+    '--cpu-prof',
+    '--cpu-prof-interval',
+    process.env.CPU_PROF_INTERVAL || '100'
+  ]
 });