src: reduce scope of code cache mutex

As indicated in the added comment, this can lead to a deadlock otherwise. In the concrete instance in which I encountered this, the relevant nested call is the one to `require('internal/tty')` inside of the `afterInspector()` function for uncaught exception handling. PR-URL: #33980 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Gus Caplan <me@gus.host> Reviewed-By: David Carlier <devnexen@gmail.com> Reviewed-By: Zeyu Yang <himself65@outlook.com> Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
nodejs · Jun 27, 2020 · 0dd67d992ec3a9a4baa5946d9c8d86df27b33e2c · 0dd67d9
1 parent 0eed22d
commit 0dd67d992ec3a9a4baa5946d9c8d86df27b33e2c
Showing with 12 additions and 4 deletions.

+12 −4 src/node_native_module.cc
diff --git a/src/node_native_module.cc b/src/node_native_module.cc
@@ -260,10 +260,13 @@ MaybeLocal<Function> NativeModuleLoader::LookupAndCompile(
   Local<Integer> column_offset = Integer::New(isolate, 0);
   ScriptOrigin origin(filename, line_offset, column_offset, True(isolate));
 
-  Mutex::ScopedLock lock(code_cache_mutex_);
-
   ScriptCompiler::CachedData* cached_data = nullptr;
   {
+    // Note: The lock here should not extend into the
+    // `CompileFunctionInContext()` call below, because this function may
+    // recurse if there is a syntax error during bootstrap (because the fatal
+    // exception handler is invoked, which may load built-in modules).
+    Mutex::ScopedLock lock(code_cache_mutex_);
     auto cache_it = code_cache_.find(id);
     if (cache_it != code_cache_.end()) {
       // Transfer ownership to ScriptCompiler::Source later.
@@ -310,8 +313,13 @@ MaybeLocal<Function> NativeModuleLoader::LookupAndCompile(
       ScriptCompiler::CreateCodeCacheForFunction(fun));
   CHECK_NOT_NULL(new_cached_data);
 
-  // The old entry should've been erased by now so we can just emplace
-  code_cache_.emplace(id, std::move(new_cached_data));
+  {
+    Mutex::ScopedLock lock(code_cache_mutex_);
+    // The old entry should've been erased by now so we can just emplace.
+    // If another thread did the same thing in the meantime, that should not
+    // be an issue.
+    code_cache_.emplace(id, std::move(new_cached_data));
+  }
 
   return scope.Escape(fun);
 }