lib,src: remove cpu profiler idle notifier

I added it in commit 57231d5 ("src: notify V8 profiler when we're
idle") from October 2013 as a stop-gap measure to measure CPU time
rather than wall clock time, otherwise processes that spend a lot
of time sleeping in system calls give a false impression of being
very busy.

That fix is not without drawbacks because the idle flag is set before
libuv makes I/O callbacks and cleared again after. I/O callbacks can
result into calls into JS code and executing JS code is as non-idle
as you can get.

In commit 96ffcb9 ("src: reduce cpu profiler overhead") from January
2015, I made Node.js block off the SIGPROF signal that V8's CPU profiler
uses before Node.js goes to sleep. The goal of that commit is to reduce
the overhead from EINTR system call wakeups but it also has the pleasant
side effect of fixing what the idle notifier tried to fix.

This commit removes the idle notifier and turns the JS process object
methods into no-ops.

Fixes: #19009
Refs: #33138

PR-URL: #34010
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/internal/bootstrap/switches/is_main_thread.js

@@ -6,8 +6,12 @@ const rawMethods = internalBinding('process_methods');
 // TODO(joyeecheung): deprecate and remove these underscore methods
 process._debugProcess = rawMethods._debugProcess;
 process._debugEnd = rawMethods._debugEnd;
-process._startProfilerIdleNotifier = rawMethods._startProfilerIdleNotifier;
-process._stopProfilerIdleNotifier = rawMethods._stopProfilerIdleNotifier;
+
+// See the discussion in https://github.com/nodejs/node/issues/19009 and
+// https://github.com/nodejs/node/pull/34010 for why these are no-ops.
+// Five word summary: they were broken beyond repair.
+process._startProfilerIdleNotifier = () => {};
+process._stopProfilerIdleNotifier = () => {};
 
 function defineStream(name, getter) {
   ObjectDefineProperty(process, name, {

lib/internal/bootstrap/switches/is_not_main_thread.js

@@ -4,8 +4,6 @@ const { ObjectDefineProperty } = primordials;
 
 delete process._debugProcess;
 delete process._debugEnd;
-delete process._startProfilerIdleNotifier;
-delete process._stopProfilerIdleNotifier;
 
 function defineStream(name, getter) {
   ObjectDefineProperty(process, name, {

src/api/environment.cc

@@ -420,7 +420,7 @@ MaybeLocal<Value> LoadEnvironment(
     Environment* env,
     StartExecutionCallback cb,
     std::unique_ptr<InspectorParentHandle> removeme) {
-  env->InitializeLibuv(per_process::v8_is_profiling);
+  env->InitializeLibuv();
   env->InitializeDiagnostics();
 
   return StartExecution(env, cb);

src/env-inl.h

@@ -378,10 +378,6 @@ inline Environment* Environment::GetThreadLocalEnv() {
   return static_cast<Environment*>(uv_key_get(&thread_local_env));
 }
 
-inline bool Environment::profiler_idle_notifier_started() const {
-  return profiler_idle_notifier_started_;
-}
-
 inline v8::Isolate* Environment::isolate() const {
   return isolate_;
 }

src/env.cc

@@ -485,7 +485,7 @@ Environment::~Environment() {
   CHECK_EQ(base_object_count_, 0);
 }
 
-void Environment::InitializeLibuv(bool start_profiler_idle_notifier) {
+void Environment::InitializeLibuv() {
   HandleScope handle_scope(isolate());
   Context::Scope context_scope(context());
 
@@ -499,17 +499,6 @@ void Environment::InitializeLibuv(bool start_profiler_idle_notifier) {
 
   uv_check_start(immediate_check_handle(), CheckImmediate);
 
-  // Inform V8's CPU profiler when we're idle.  The profiler is sampling-based
-  // but not all samples are created equal; mark the wall clock time spent in
-  // epoll_wait() and friends so profiling tools can filter it out.  The samples
-  // still end up in v8.log but with state=IDLE rather than state=EXTERNAL.
-  // TODO(bnoordhuis) Depends on a libuv implementation detail that we should
-  // probably fortify in the API contract, namely that the last started prepare
-  // or check watcher runs first.  It's not 100% foolproof; if an add-on starts
-  // a prepare or check watcher after us, any samples attributed to its callback
-  // will be recorded with state=IDLE.
-  uv_prepare_init(event_loop(), &idle_prepare_handle_);
-  uv_check_init(event_loop(), &idle_check_handle_);
   uv_async_init(
       event_loop(),
       &task_queues_async_,
@@ -518,8 +507,6 @@ void Environment::InitializeLibuv(bool start_profiler_idle_notifier) {
             &Environment::task_queues_async_, async);
         env->RunAndClearNativeImmediates();
       });
-  uv_unref(reinterpret_cast<uv_handle_t*>(&idle_prepare_handle_));
-  uv_unref(reinterpret_cast<uv_handle_t*>(&idle_check_handle_));
   uv_unref(reinterpret_cast<uv_handle_t*>(&task_queues_async_));
 
   {
@@ -536,10 +523,6 @@ void Environment::InitializeLibuv(bool start_profiler_idle_notifier) {
   // the one environment per process setup, but will be called in
   // FreeEnvironment.
   RegisterHandleCleanups();
-
-  if (start_profiler_idle_notifier) {
-    StartProfilerIdleNotifier();
-  }
 }
 
 void Environment::ExitEnv() {
@@ -567,8 +550,6 @@ void Environment::RegisterHandleCleanups() {
   register_handle(reinterpret_cast<uv_handle_t*>(timer_handle()));
   register_handle(reinterpret_cast<uv_handle_t*>(immediate_check_handle()));
   register_handle(reinterpret_cast<uv_handle_t*>(immediate_idle_handle()));
-  register_handle(reinterpret_cast<uv_handle_t*>(&idle_prepare_handle_));
-  register_handle(reinterpret_cast<uv_handle_t*>(&idle_check_handle_));
   register_handle(reinterpret_cast<uv_handle_t*>(&task_queues_async_));
 }
 
@@ -600,29 +581,6 @@ void Environment::CleanupHandles() {
   }
 }
 
-void Environment::StartProfilerIdleNotifier() {
-  if (profiler_idle_notifier_started_)
-    return;
-
-  profiler_idle_notifier_started_ = true;
-
-  uv_prepare_start(&idle_prepare_handle_, [](uv_prepare_t* handle) {
-    Environment* env = ContainerOf(&Environment::idle_prepare_handle_, handle);
-    env->isolate()->SetIdle(true);
-  });
-
-  uv_check_start(&idle_check_handle_, [](uv_check_t* handle) {
-    Environment* env = ContainerOf(&Environment::idle_check_handle_, handle);
-    env->isolate()->SetIdle(false);
-  });
-}
-
-void Environment::StopProfilerIdleNotifier() {
-  profiler_idle_notifier_started_ = false;
-  uv_prepare_stop(&idle_prepare_handle_);
-  uv_check_stop(&idle_check_handle_);
-}
-
 void Environment::PrintSyncTrace() const {
   if (!trace_sync_io_) return;
 

src/env.h

@@ -879,7 +879,7 @@ class Environment : public MemoryRetainer {
               ThreadId thread_id);
   ~Environment() override;
 
-  void InitializeLibuv(bool start_profiler_idle_notifier);
+  void InitializeLibuv();
   inline const std::vector<std::string>& exec_argv();
   inline const std::vector<std::string>& argv();
   const std::string& exec_path() const;
@@ -909,10 +909,6 @@ class Environment : public MemoryRetainer {
   inline void AssignToContext(v8::Local<v8::Context> context,
                               const ContextInfo& info);
 
-  void StartProfilerIdleNotifier();
-  void StopProfilerIdleNotifier();
-  inline bool profiler_idle_notifier_started() const;
-
   inline v8::Isolate* isolate() const;
   inline uv_loop_t* event_loop() const;
   inline void TryLoadAddon(
@@ -1234,11 +1230,8 @@ class Environment : public MemoryRetainer {
   uv_timer_t timer_handle_;
   uv_check_t immediate_check_handle_;
   uv_idle_t immediate_idle_handle_;
-  uv_prepare_t idle_prepare_handle_;
-  uv_check_t idle_check_handle_;
   uv_async_t task_queues_async_;
   int64_t task_queues_async_refs_ = 0;
-  bool profiler_idle_notifier_started_ = false;
 
   AsyncHooks async_hooks_;
   ImmediateInfo immediate_info_;

src/node.cc

@@ -148,8 +148,6 @@ bool v8_initialized = false;
 // node_internals.h
 // process-relative uptime base in nanoseconds, initialized in node::Start()
 uint64_t node_start_time;
-// Tells whether --prof is passed.
-bool v8_is_profiling = false;
 
 // node_v8_platform-inl.h
 struct V8Platform v8_platform;
@@ -789,19 +787,11 @@ int ProcessGlobalArgs(std::vector<std::string>* args,
     env_opts->abort_on_uncaught_exception = true;
   }
 
-  // TODO(bnoordhuis) Intercept --prof arguments and start the CPU profiler
-  // manually?  That would give us a little more control over its runtime
-  // behavior but it could also interfere with the user's intentions in ways
-  // we fail to anticipate.  Dillema.
-  if (std::find(v8_args.begin(), v8_args.end(), "--prof") != v8_args.end()) {
-    per_process::v8_is_profiling = true;
-  }
-
 #ifdef __POSIX__
   // Block SIGPROF signals when sleeping in epoll_wait/kevent/etc.  Avoids the
   // performance penalty of frequent EINTR wakeups when the profiler is running.
   // Only do this for v8.log profiling, as it breaks v8::CpuProfiler users.
-  if (per_process::v8_is_profiling) {
+  if (std::find(v8_args.begin(), v8_args.end(), "--prof") != v8_args.end()) {
     uv_loop_configure(uv_default_loop(), UV_LOOP_BLOCK_SIGNAL, SIGPROF);
   }
 #endif

src/node_internals.h

@@ -55,7 +55,6 @@ class NativeModuleLoader;
 namespace per_process {
 extern Mutex env_var_mutex;
 extern uint64_t node_start_time;
-extern bool v8_is_profiling;
 }  // namespace per_process
 
 // Forward declaration

src/node_process_methods.cc

@@ -224,16 +224,6 @@ void RawDebug(const FunctionCallbackInfo<Value>& args) {
   fflush(stderr);
 }
 
-static void StartProfilerIdleNotifier(const FunctionCallbackInfo<Value>& args) {
-  Environment* env = Environment::GetCurrent(args);
-  env->StartProfilerIdleNotifier();
-}
-
-static void StopProfilerIdleNotifier(const FunctionCallbackInfo<Value>& args) {
-  Environment* env = Environment::GetCurrent(args);
-  env->StopProfilerIdleNotifier();
-}
-
 static void Umask(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
   CHECK(env->has_run_bootstrapping_code());
@@ -456,10 +446,6 @@ static void InitializeProcessMethods(Local<Object> target,
     env->SetMethod(target, "chdir", Chdir);
   }
 
-  env->SetMethod(
-      target, "_startProfilerIdleNotifier", StartProfilerIdleNotifier);
-  env->SetMethod(target, "_stopProfilerIdleNotifier", StopProfilerIdleNotifier);
-
   env->SetMethod(target, "umask", Umask);
   env->SetMethod(target, "_rawDebug", RawDebug);
   env->SetMethod(target, "memoryUsage", MemoryUsage);