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src: give Http2Session JS fields their own backing store
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It looks like it’s virtually impossible at this point to
create “fake” backing stores for objects that don’t fully
own their memory allocations, like the sub-field `js_fields_`
of `Http2Session`. In particular, it turns out that an
`ArrayBuffer` cannot always be easily separated from its
backing store in that situation through by detaching it.

This commit gives the JS-exposed parts of the class its own
memory allocation and its own backing store, simplifying the
code a bit and fixing flakiness coming from it, at the cost
of one additional layer of indirection when accessing the data.

Refs: #30782
Fixes: #31107

PR-URL: #31648
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Denys Otrishko <shishugi@gmail.com>
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@addaleax
addaleax committed Feb 8, 2020
1 parent 3271c40 commit f368210
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Showing 2 changed files with 21 additions and 40 deletions.
57 changes: 19 additions & 38 deletions src/node_http2.cc
View file
Original file line number Diff line number Diff line change
Expand Up @@ -568,42 +568,23 @@ Http2Session::Http2Session(Environment* env,
outgoing_storage_.reserve(1024);
outgoing_buffers_.reserve(32);

{
// Make the js_fields_ property accessible to JS land.
std::unique_ptr<BackingStore> backing =
ArrayBuffer::NewBackingStore(
reinterpret_cast<uint8_t*>(&js_fields_),
kSessionUint8FieldCount,
[](void*, size_t, void*){},
nullptr);
Local<ArrayBuffer> ab =
ArrayBuffer::New(env->isolate(), std::move(backing));
// TODO(thangktran): drop this check when V8 is pumped to 8.0 .
if (!ab->IsExternal())
ab->Externalize(ab->GetBackingStore());
ab->SetPrivate(env->context(),
env->arraybuffer_untransferable_private_symbol(),
True(env->isolate())).Check();
js_fields_ab_.Reset(env->isolate(), ab);
Local<Uint8Array> uint8_arr =
Uint8Array::New(ab, 0, kSessionUint8FieldCount);
USE(wrap->Set(env->context(), env->fields_string(), uint8_arr));
}
// Make the js_fields_ property accessible to JS land.
js_fields_store_ =
ArrayBuffer::NewBackingStore(env->isolate(), sizeof(SessionJSFields));
js_fields_ = new(js_fields_store_->Data()) SessionJSFields;

Local<ArrayBuffer> ab = ArrayBuffer::New(env->isolate(), js_fields_store_);
Local<Uint8Array> uint8_arr =
Uint8Array::New(ab, 0, kSessionUint8FieldCount);
USE(wrap->Set(env->context(), env->fields_string(), uint8_arr));
}

Http2Session::~Http2Session() {
CHECK_EQ(flags_ & SESSION_STATE_HAS_SCOPE, 0);
Debug(this, "freeing nghttp2 session");
nghttp2_session_del(session_);
CHECK_EQ(current_nghttp2_memory_, 0);
HandleScope handle_scope(env()->isolate());
// Detach js_fields_ab_ to avoid having problem when new Http2Session
// instances are created on the same location of previous
// instances. This in turn will call ArrayBuffer::NewBackingStore()
// multiple times with the same buffer address and causing error.
// Ref: https://github.com/nodejs/node/pull/30782
Local<ArrayBuffer> ab = js_fields_ab_.Get(env()->isolate());
ab->Detach();
js_fields_->~SessionJSFields();
}

std::string Http2Session::diagnostic_name() const {
Expand Down Expand Up @@ -871,7 +852,7 @@ int Http2Session::OnBeginHeadersCallback(nghttp2_session* handle,
Http2Stream::New(session, id, frame->headers.cat) ==
nullptr)) {
if (session->rejected_stream_count_++ >
session->js_fields_.max_rejected_streams)
session->js_fields_->max_rejected_streams)
return NGHTTP2_ERR_CALLBACK_FAILURE;
// Too many concurrent streams being opened
nghttp2_submit_rst_stream(**session, NGHTTP2_FLAG_NONE, id,
Expand Down Expand Up @@ -965,9 +946,9 @@ int Http2Session::OnInvalidFrame(nghttp2_session* handle,
Debug(session,
"invalid frame received (%u/%u), code: %d",
session->invalid_frame_count_,
session->js_fields_.max_invalid_frames,
session->js_fields_->max_invalid_frames,
lib_error_code);
if (session->invalid_frame_count_++ > session->js_fields_.max_invalid_frames)
if (session->invalid_frame_count_++ > session->js_fields_->max_invalid_frames)
return 1;

// If the error is fatal or if error code is ERR_STREAM_CLOSED... emit error
Expand Down Expand Up @@ -1003,7 +984,7 @@ int Http2Session::OnFrameNotSent(nghttp2_session* handle,
if (error_code == NGHTTP2_ERR_SESSION_CLOSING ||
error_code == NGHTTP2_ERR_STREAM_CLOSED ||
error_code == NGHTTP2_ERR_STREAM_CLOSING ||
session->js_fields_.frame_error_listener_count == 0) {
session->js_fields_->frame_error_listener_count == 0) {
return 0;
}

Expand Down Expand Up @@ -1306,7 +1287,7 @@ void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
// are considered advisory only, so this has no real effect other than to
// simply let user code know that the priority has changed.
void Http2Session::HandlePriorityFrame(const nghttp2_frame* frame) {
if (js_fields_.priority_listener_count == 0) return;
if (js_fields_->priority_listener_count == 0) return;
Isolate* isolate = env()->isolate();
HandleScope scope(isolate);
Local<Context> context = env()->context();
Expand Down Expand Up @@ -1375,7 +1356,7 @@ void Http2Session::HandleGoawayFrame(const nghttp2_frame* frame) {

// Called by OnFrameReceived when a complete ALTSVC frame has been received.
void Http2Session::HandleAltSvcFrame(const nghttp2_frame* frame) {
if (!(js_fields_.bitfield & (1 << kSessionHasAltsvcListeners))) return;
if (!(js_fields_->bitfield & (1 << kSessionHasAltsvcListeners))) return;
Isolate* isolate = env()->isolate();
HandleScope scope(isolate);
Local<Context> context = env()->context();
Expand Down Expand Up @@ -1454,7 +1435,7 @@ void Http2Session::HandlePingFrame(const nghttp2_frame* frame) {
return;
}

if (!(js_fields_.bitfield & (1 << kSessionHasPingListeners))) return;
if (!(js_fields_->bitfield & (1 << kSessionHasPingListeners))) return;
// Notify the session that a ping occurred
arg = Buffer::Copy(env(),
reinterpret_cast<const char*>(frame->ping.opaque_data),
Expand All @@ -1466,8 +1447,8 @@ void Http2Session::HandlePingFrame(const nghttp2_frame* frame) {
void Http2Session::HandleSettingsFrame(const nghttp2_frame* frame) {
bool ack = frame->hd.flags & NGHTTP2_FLAG_ACK;
if (!ack) {
js_fields_.bitfield &= ~(1 << kSessionRemoteSettingsIsUpToDate);
if (!(js_fields_.bitfield & (1 << kSessionHasRemoteSettingsListeners)))
js_fields_->bitfield &= ~(1 << kSessionRemoteSettingsIsUpToDate);
if (!(js_fields_->bitfield & (1 << kSessionHasRemoteSettingsListeners)))
return;
// This is not a SETTINGS acknowledgement, notify and return
MakeCallback(env()->http2session_on_settings_function(), 0, nullptr);
Expand Down
4 changes: 2 additions & 2 deletions src/node_http2.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -990,8 +990,8 @@ class Http2Session : public AsyncWrap,
nghttp2_session* session_;

// JS-accessible numeric fields, as indexed by SessionUint8Fields.
SessionJSFields js_fields_ = {};
v8::Global<v8::ArrayBuffer> js_fields_ab_;
SessionJSFields* js_fields_ = nullptr;
std::shared_ptr<v8::BackingStore> js_fields_store_;

// The session type: client or server
nghttp2_session_type session_type_;
Expand Down

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