tracing: forbid tracing modifications from worker threads

Forbid modifying tracing state from worker threads, either
through the built-in module or inspector sessions, since
the main thread owns all global state, and at least
the `async_hooks` integration is definitely not thread
safe in its current state.

doc/api/worker_threads.md

@@ -253,6 +253,7 @@ Notable differences inside a Worker environment are:
 - Execution may stop at any point as a result of [`worker.terminate()`][]
   being invoked.
 - IPC channels from parent processes are not accessible.
+- The [`trace_events`][] module is not supported.
 
 Currently, the following differences also exist until they are addressed:
 
@@ -489,6 +490,7 @@ active handle in the event system. If the worker is already `unref()`ed calling
 [`SharedArrayBuffer`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer
 [Signals events]: process.html#process_signal_events
 [`Uint8Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array
+[`trace_events`]: tracing.html
 [browser `MessagePort`]: https://developer.mozilla.org/en-US/docs/Web/API/MessagePort
 [child processes]: child_process.html
 [HTML structured clone algorithm]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm

lib/trace_events.js

@@ -13,7 +13,8 @@ const {
   ERR_INVALID_ARG_TYPE
 } = require('internal/errors').codes;
 
-if (!hasTracing)
+const { isMainThread } = require('internal/worker');
+if (!hasTracing || !isMainThread)
   throw new ERR_TRACE_EVENTS_UNAVAILABLE();
 
 const { CategorySet, getEnabledCategories } = internalBinding('trace_events');

src/env.cc

@@ -128,11 +128,22 @@ void InitThreadLocalOnce() {
 }
 
 void Environment::TrackingTraceStateObserver::UpdateTraceCategoryState() {
+  if (!env_->is_main_thread()) {
+    // Ideally, we’d have a consistent story that treats all threads/Environment
+    // instances equally here. However, tracing is essentially global, and this
+    // callback is callback from whichever thread calls `StartTracing()` or
+    // `StopTracing()`. The only way to do this in a threadsafe fashion
+    // seems to be only tracking this from the main thread, and only allowing
+    // these state modifications from the main thread.
+    return;
+  }
+
   env_->trace_category_state()[0] =
       *TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(
           TRACING_CATEGORY_NODE1(async_hooks));
 
   Isolate* isolate = env_->isolate();
+  HandleScope handle_scope(isolate);
   Local<Function> cb = env_->trace_category_state_function();
   if (cb.IsEmpty())
     return;

src/inspector/tracing_agent.cc

@@ -65,6 +65,10 @@ DispatchResponse TracingAgent::start(
     return DispatchResponse::Error(
         "Call NodeTracing::end to stop tracing before updating the config");
   }
+  if (!env_->is_main_thread()) {
+    return DispatchResponse::Error(
+        "Tracing properties can only be changed through main thread sessions");
+  }
 
   std::set<std::string> categories_set;
   protocol::Array<std::string>* categories =