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src: add check against non-weak BaseObjects at process exit #35490

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6 changes: 6 additions & 0 deletions src/async_wrap.cc
Original file line number Diff line number Diff line change
Expand Up @@ -99,6 +99,12 @@ struct AsyncWrapObject : public AsyncWrap {
return tmpl;
}

bool IsNotIndicativeOfMemoryLeakAtExit() const override {
// We can't really know what the underlying operation does. One of the
// signs that it's time to remove this class. :)
return true;
}

SET_NO_MEMORY_INFO()
SET_MEMORY_INFO_NAME(AsyncWrapObject)
SET_SELF_SIZE(AsyncWrapObject)
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7 changes: 7 additions & 0 deletions src/base_object-inl.h
Original file line number Diff line number Diff line change
Expand Up @@ -146,6 +146,13 @@ void BaseObject::ClearWeak() {
persistent_handle_.ClearWeak();
}

bool BaseObject::IsWeakOrDetached() const {
if (persistent_handle_.IsWeak()) return true;

if (!has_pointer_data()) return false;
const PointerData* pd = const_cast<BaseObject*>(this)->pointer_data();
return pd->wants_weak_jsobj || pd->is_detached;
}

v8::Local<v8::FunctionTemplate>
BaseObject::MakeLazilyInitializedJSTemplate(Environment* env) {
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9 changes: 9 additions & 0 deletions src/base_object.h
Original file line number Diff line number Diff line change
Expand Up @@ -78,6 +78,11 @@ class BaseObject : public MemoryRetainer {
// root and will not be touched by the garbage collector.
inline void ClearWeak();

// Reports whether this BaseObject is using a weak reference or detached,
// i.e. whether is can be deleted by GC once no strong BaseObjectPtrs refer
// to it anymore.
inline bool IsWeakOrDetached() const;

// Utility to create a FunctionTemplate with one internal field (used for
// the `BaseObject*` pointer) and a constructor that initializes that field
// to `nullptr`.
Expand Down Expand Up @@ -147,6 +152,10 @@ class BaseObject : public MemoryRetainer {
virtual v8::Maybe<bool> FinalizeTransferRead(
v8::Local<v8::Context> context, v8::ValueDeserializer* deserializer);

// Indicates whether this object is expected to use a strong reference during
// a clean process exit (due to an empty event loop).
virtual bool IsNotIndicativeOfMemoryLeakAtExit() const;

virtual inline void OnGCCollect();

private:
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51 changes: 38 additions & 13 deletions src/env.cc
Original file line number Diff line number Diff line change
Expand Up @@ -1194,22 +1194,43 @@ void Environment::RemoveUnmanagedFd(int fd) {
}
}

void Environment::ForEachBaseObject(BaseObjectIterator iterator) {
void Environment::PrintAllBaseObjects() {
size_t i = 0;
for (const auto& hook : cleanup_hooks_) {
BaseObject* obj = hook.GetBaseObject();
if (obj != nullptr) iterator(i, obj);
i++;
}
}

void PrintBaseObject(size_t i, BaseObject* obj) {
std::cout << "#" << i << " " << obj << ": " << obj->MemoryInfoName() << "\n";
std::cout << "BaseObjects\n";
ForEachBaseObject([&](BaseObject* obj) {
std::cout << "#" << i++ << " " << obj << ": " <<
obj->MemoryInfoName() << "\n";
});
}

void Environment::PrintAllBaseObjects() {
std::cout << "BaseObjects\n";
ForEachBaseObject(PrintBaseObject);
void Environment::VerifyNoStrongBaseObjects() {
// When a process exits cleanly, i.e. because the event loop ends up without
// things to wait for, the Node.js objects that are left on the heap should
// be:
//
// 1. weak, i.e. ready for garbage collection once no longer referenced, or
// 2. detached, i.e. scheduled for destruction once no longer referenced, or
// 3. an unrefed libuv handle, i.e. does not keep the event loop alive, or
// 4. an inactive libuv handle (essentially the same here)
//
// There are a few exceptions to this rule, but generally, if there are
// C++-backed Node.js objects on the heap that do not fall into the above
// categories, we may be looking at a potential memory leak. Most likely,
// the cause is a missing MakeWeak() call on the corresponding object.
//
// In order to avoid this kind of problem, we check the list of BaseObjects
// for these criteria. Currently, we only do so when explicitly instructed to
// or when in debug mode (where --verify-base-objects is always-on).

if (!options()->verify_base_objects) return;

ForEachBaseObject([this](BaseObject* obj) {
if (obj->IsNotIndicativeOfMemoryLeakAtExit()) return;
fprintf(stderr, "Found bad BaseObject during clean exit: %s\n",
obj->MemoryInfoName().c_str());
fflush(stderr);
ABORT();
});
}

EnvSerializeInfo Environment::Serialize(SnapshotCreator* creator) {
Expand Down Expand Up @@ -1473,4 +1494,8 @@ Local<FunctionTemplate> BaseObject::GetConstructorTemplate(Environment* env) {
return tmpl;
}

bool BaseObject::IsNotIndicativeOfMemoryLeakAtExit() const {
return IsWeakOrDetached();
}
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} // namespace node
3 changes: 1 addition & 2 deletions src/env.h
Original file line number Diff line number Diff line change
Expand Up @@ -934,9 +934,8 @@ class Environment : public MemoryRetainer {
void CreateProperties();
void DeserializeProperties(const EnvSerializeInfo* info);

typedef void (*BaseObjectIterator)(size_t, BaseObject*);
void ForEachBaseObject(BaseObjectIterator iterator);
void PrintAllBaseObjects();
void VerifyNoStrongBaseObjects();
// Should be called before InitializeInspector()
void InitializeDiagnostics();
#if HAVE_INSPECTOR
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7 changes: 7 additions & 0 deletions src/handle_wrap.cc
Original file line number Diff line number Diff line change
Expand Up @@ -89,6 +89,13 @@ void HandleWrap::OnGCCollect() {
}


bool HandleWrap::IsNotIndicativeOfMemoryLeakAtExit() const {
return IsWeakOrDetached() ||
!HandleWrap::HasRef(this) ||
!uv_is_active(GetHandle());
}


void HandleWrap::MarkAsInitialized() {
env()->handle_wrap_queue()->PushBack(this);
state_ = kInitialized;
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1 change: 1 addition & 0 deletions src/handle_wrap.h
Original file line number Diff line number Diff line change
Expand Up @@ -87,6 +87,7 @@ class HandleWrap : public AsyncWrap {
AsyncWrap::ProviderType provider);
virtual void OnClose() {}
void OnGCCollect() final;
bool IsNotIndicativeOfMemoryLeakAtExit() const override;

void MarkAsInitialized();
void MarkAsUninitialized();
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4 changes: 4 additions & 0 deletions src/inspector_js_api.cc
Original file line number Diff line number Diff line change
Expand Up @@ -156,6 +156,10 @@ class JSBindingsConnection : public AsyncWrap {
SET_MEMORY_INFO_NAME(JSBindingsConnection)
SET_SELF_SIZE(JSBindingsConnection)

bool IsNotIndicativeOfMemoryLeakAtExit() const override {
return true; // Binding connections emit events on their own.
}

private:
std::unique_ptr<InspectorSession> session_;
Global<Function> callback_;
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6 changes: 6 additions & 0 deletions src/module_wrap.h
Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,12 @@ class ModuleWrap : public BaseObject {
SET_MEMORY_INFO_NAME(ModuleWrap)
SET_SELF_SIZE(ModuleWrap)

bool IsNotIndicativeOfMemoryLeakAtExit() const override {
// XXX: The garbage collection rules for ModuleWrap are *super* unclear.
// Do these objects ever get GC'd? Are we just okay with leaking them?
return true;
}
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I know the bot already pinged the team, but I’d be curious to know if @nodejs/modules knows more about this … especially for ModuleWraps created by the vm module, creating non-GC-able objects can’t be ideal, right…?

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I thought they were all weak at one point?


private:
ModuleWrap(Environment* env,
v8::Local<v8::Object> object,
Expand Down
2 changes: 2 additions & 0 deletions src/node_contextify.h
Original file line number Diff line number Diff line change
Expand Up @@ -174,6 +174,8 @@ class CompiledFnEntry final : public BaseObject {
v8::Local<v8::ScriptOrModule> script);
~CompiledFnEntry();

bool IsNotIndicativeOfMemoryLeakAtExit() const override { return true; }

private:
uint32_t id_;
v8::Global<v8::ScriptOrModule> script_;
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9 changes: 9 additions & 0 deletions src/node_http_parser.cc
Original file line number Diff line number Diff line change
Expand Up @@ -880,6 +880,15 @@ class Parser : public AsyncWrap, public StreamListener {
return HPE_PAUSED;
}


bool IsNotIndicativeOfMemoryLeakAtExit() const override {
// HTTP parsers are able to emit events without any GC root referring
// to them, because they receive events directly from the underlying
// libuv resource.
return true;
}


llhttp_t parser_;
StringPtr fields_[kMaxHeaderFieldsCount]; // header fields
StringPtr values_[kMaxHeaderFieldsCount]; // header values
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1 change: 1 addition & 0 deletions src/node_main_instance.cc
Original file line number Diff line number Diff line change
Expand Up @@ -168,6 +168,7 @@ int NodeMainInstance::Run(const EnvSerializeInfo* env_info) {
}

env->set_trace_sync_io(false);
if (!env->is_stopping()) env->VerifyNoStrongBaseObjects();
exit_code = EmitExit(env.get());
}

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4 changes: 4 additions & 0 deletions src/node_options.cc
Original file line number Diff line number Diff line change
Expand Up @@ -475,6 +475,10 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
"an error), 'warn' (enforce warnings) or 'none' (silence warnings)",
&EnvironmentOptions::unhandled_rejections,
kAllowedInEnvironment);
AddOption("--verify-base-objects",
"", /* undocumented, only for debugging */
&EnvironmentOptions::verify_base_objects,
kAllowedInEnvironment);

AddOption("--check",
"syntax check script without executing",
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6 changes: 6 additions & 0 deletions src/node_options.h
Original file line number Diff line number Diff line change
Expand Up @@ -150,6 +150,12 @@ class EnvironmentOptions : public Options {
bool trace_warnings = false;
std::string unhandled_rejections;
std::string userland_loader;
bool verify_base_objects =
#ifdef DEBUG
true;
#else
false;
#endif // DEBUG

bool syntax_check_only = false;
bool has_eval_string = false;
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10 changes: 9 additions & 1 deletion src/node_worker.cc
Original file line number Diff line number Diff line change
Expand Up @@ -362,8 +362,10 @@ void Worker::Run() {
{
int exit_code;
bool stopped = is_stopped();
if (!stopped)
if (!stopped) {
env_->VerifyNoStrongBaseObjects();
exit_code = EmitExit(env_.get());
}
Mutex::ScopedLock lock(mutex_);
if (exit_code_ == 0 && !stopped)
exit_code_ = exit_code;
Expand Down Expand Up @@ -714,6 +716,12 @@ void Worker::MemoryInfo(MemoryTracker* tracker) const {
tracker->TrackField("parent_port", parent_port_);
}

bool Worker::IsNotIndicativeOfMemoryLeakAtExit() const {
// Worker objects always stay alive as long as the child thread, regardless
// of whether they are being referenced in the parent thread.
return true;
}

class WorkerHeapSnapshotTaker : public AsyncWrap {
public:
WorkerHeapSnapshotTaker(Environment* env, Local<Object> obj)
Expand Down
1 change: 1 addition & 0 deletions src/node_worker.h
Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,7 @@ class Worker : public AsyncWrap {
void MemoryInfo(MemoryTracker* tracker) const override;
SET_MEMORY_INFO_NAME(Worker)
SET_SELF_SIZE(Worker)
bool IsNotIndicativeOfMemoryLeakAtExit() const override;

bool is_stopped() const;

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8 changes: 8 additions & 0 deletions src/stream_base.h
Original file line number Diff line number Diff line change
Expand Up @@ -412,6 +412,10 @@ class SimpleShutdownWrap : public ShutdownWrap, public OtherBase {
SET_NO_MEMORY_INFO()
SET_MEMORY_INFO_NAME(SimpleShutdownWrap)
SET_SELF_SIZE(SimpleShutdownWrap)

bool IsNotIndicativeOfMemoryLeakAtExit() const override {
return OtherBase::IsNotIndicativeOfMemoryLeakAtExit();
}
};

template <typename OtherBase>
Expand All @@ -425,6 +429,10 @@ class SimpleWriteWrap : public WriteWrap, public OtherBase {
SET_NO_MEMORY_INFO()
SET_MEMORY_INFO_NAME(SimpleWriteWrap)
SET_SELF_SIZE(SimpleWriteWrap)

bool IsNotIndicativeOfMemoryLeakAtExit() const override {
return OtherBase::IsNotIndicativeOfMemoryLeakAtExit();
}
};

} // namespace node
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Original file line number Diff line number Diff line change
Expand Up @@ -88,6 +88,7 @@ assert(undocumented.delete('--experimental-report'));
assert(undocumented.delete('--experimental-worker'));
assert(undocumented.delete('--no-node-snapshot'));
assert(undocumented.delete('--loader'));
assert(undocumented.delete('--verify-base-objects'));

assert.strictEqual(undocumented.size, 0,
'The following options are not documented as allowed in ' +
Expand Down