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worker: refactor thread life cycle management
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The current mechanism of uses two async handles, one owned by the
creator of the worker thread to terminate a running worker,
and another one employed by the worker to interrupt its creator on its
natural termination. The force termination piggybacks on the message-
passing mechanism to inform the worker to quiesce.

Also there are few flags that represent the other thread's state /
request state because certain code path is shared by multiple
control flows, and there are certain code path where the async
handles may not have come to life.

Refactor into a LoopStopper abstraction that exposes routines to
install a handle as well as to save a state.

Refs: nodejs#21283
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@gireeshpunathil
gireeshpunathil committed Mar 1, 2019
1 parent 5843058 commit fbf740e
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Showing 4 changed files with 103 additions and 95 deletions.
16 changes: 0 additions & 16 deletions src/node_messaging.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -584,13 +584,6 @@ void MessagePort::OnMessage() {
// Get the head of the message queue.
Mutex::ScopedLock lock(data_->mutex_);

if (stop_event_loop_) {
Debug(this, "MessagePort stops loop as requested");
CHECK(!data_->receiving_messages_);
uv_stop(env()->event_loop());
break;
}

Debug(this, "MessagePort has message, receiving = %d",
static_cast<int>(data_->receiving_messages_));

Expand Down Expand Up @@ -740,15 +733,6 @@ void MessagePort::Stop() {
data_->receiving_messages_ = false;
}

void MessagePort::StopEventLoop() {
Mutex::ScopedLock lock(data_->mutex_);
data_->receiving_messages_ = false;
stop_event_loop_ = true;

Debug(this, "Received StopEventLoop request");
TriggerAsync();
}

void MessagePort::Start(const FunctionCallbackInfo<Value>& args) {
Environment* env = Environment::GetCurrent(args);
MessagePort* port;
Expand Down
4 changes: 0 additions & 4 deletions src/node_messaging.h
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Original file line number Diff line number Diff line change
Expand Up @@ -159,9 +159,6 @@ class MessagePort : public HandleWrap {
void Start();
// Stop processing messages on this port as a receiving end.
void Stop();
// Stop processing messages on this port as a receiving end,
// and stop the event loop that this port is associated with.
void StopEventLoop();

static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static void PostMessage(const v8::FunctionCallbackInfo<v8::Value>& args);
Expand Down Expand Up @@ -206,7 +203,6 @@ class MessagePort : public HandleWrap {
inline uv_async_t* async();

std::unique_ptr<MessagePortData> data_ = nullptr;
bool stop_event_loop_ = false;

friend class MessagePortData;
};
Expand Down
139 changes: 77 additions & 62 deletions src/node_worker.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,46 @@ void WaitForWorkerInspectorToStop(Environment* child) {

} // anonymous namespace

void AsyncRequest::Install(Environment* env, void* data, uv_async_cb target) {
Mutex::ScopedLock lock(mutex_);
env_ = env;
async_ = new uv_async_t;
if (data != nullptr) async_->data = data;
CHECK_EQ(uv_async_init(env_->event_loop(), async_, target), 0);
}

void AsyncRequest::Uninstall() {
Mutex::ScopedLock lock(mutex_);
if (async_ != nullptr)
env_->CloseHandle(async_, [](uv_async_t* async) { delete async; });
}

void AsyncRequest::Stop() {
Mutex::ScopedLock lock(mutex_);
stop_ = true;
if (async_ != nullptr) uv_async_send(async_);
}

void AsyncRequest::SetStopped(bool flag) {
Mutex::ScopedLock lock(mutex_);
stop_ = flag;
}

bool AsyncRequest::IsStopped() {
Mutex::ScopedLock lock(mutex_);
return stop_;
}

uv_async_t* AsyncRequest::GetHandle() {
Mutex::ScopedLock lock(mutex_);
return async_;
}

void AsyncRequest::MemoryInfo(MemoryTracker* tracker) const {
Mutex::ScopedLock lock(mutex_);
if (async_ != nullptr) tracker->TrackField("async_request", *async_);
}

Worker::Worker(Environment* env,
Local<Object> wrap,
const std::string& url,
Expand Down Expand Up @@ -97,9 +137,8 @@ Worker::Worker(Environment* env,
Debug(this, "Preparation for worker %llu finished", thread_id_);
}

bool Worker::is_stopped() const {
Mutex::ScopedLock stopped_lock(stopped_mutex_);
return stopped_;
bool Worker::is_stopped() {
return thread_stopper_.IsStopped();
}

// This class contains data that is only relevant to the child thread itself,
Expand Down Expand Up @@ -207,6 +246,8 @@ void Worker::Run() {
Context::Scope context_scope(env_->context());
if (child_port != nullptr)
child_port->Close();
thread_stopper_.Uninstall();
thread_stopper_.SetStopped(true);
env_->stop_sub_worker_contexts();
env_->RunCleanup();
RunAtExit(env_.get());
Expand All @@ -215,10 +256,7 @@ void Worker::Run() {
WaitForWorkerInspectorToStop(env_.get());
#endif

{
Mutex::ScopedLock stopped_lock(stopped_mutex_);
stopped_ = true;
}
env_->RunCleanup();

// This call needs to be made while the `Environment` is still alive
// because we assume that it is available for async tracking in the
Expand All @@ -227,11 +265,12 @@ void Worker::Run() {
}
});

if (thread_stopper_.IsStopped()) return;
{
HandleScope handle_scope(isolate_);
Local<Context> context = NewContext(isolate_);
if (is_stopped()) return;

if (thread_stopper_.IsStopped()) return;
CHECK(!context.IsEmpty());
Context::Scope context_scope(context);
{
Expand All @@ -253,6 +292,14 @@ void Worker::Run() {
Debug(this, "Created Environment for worker with id %llu", thread_id_);

if (is_stopped()) return;
thread_stopper_.Install(env_.get(), env_.get(), [](uv_async_t* handle) {
Environment* env_ = static_cast<Environment*>(handle->data);
uv_stop(env_->event_loop());
});
uv_unref(reinterpret_cast<uv_handle_t*>(thread_stopper_.GetHandle()));

Debug(this, "Created Environment for worker with id %llu", thread_id_);
if (thread_stopper_.IsStopped()) return;
{
HandleScope handle_scope(isolate_);
Mutex::ScopedLock lock(mutex_);
Expand All @@ -268,7 +315,7 @@ void Worker::Run() {
Debug(this, "Created message port for worker %llu", thread_id_);
}

if (is_stopped()) return;
if (thread_stopper_.IsStopped()) return;
{
#if NODE_USE_V8_PLATFORM && HAVE_INSPECTOR
StartWorkerInspector(env_.get(),
Expand All @@ -289,22 +336,21 @@ void Worker::Run() {
Debug(this, "Loaded environment for worker %llu", thread_id_);
}

if (is_stopped()) return;
if (thread_stopper_.IsStopped()) return;
{
SealHandleScope seal(isolate_);
bool more;
env_->performance_state()->Mark(
node::performance::NODE_PERFORMANCE_MILESTONE_LOOP_START);
do {
if (is_stopped()) break;
if (thread_stopper_.IsStopped()) break;
uv_run(&data.loop_, UV_RUN_DEFAULT);
if (is_stopped()) break;
if (thread_stopper_.IsStopped()) break;

platform_->DrainTasks(isolate_);

more = uv_loop_alive(&data.loop_);
if (more && !is_stopped())
continue;
if (more && !thread_stopper_.IsStopped()) continue;

EmitBeforeExit(env_.get());

Expand All @@ -319,7 +365,7 @@ void Worker::Run() {

{
int exit_code;
bool stopped = is_stopped();
bool stopped = thread_stopper_.IsStopped();
if (!stopped)
exit_code = EmitExit(env_.get());
Mutex::ScopedLock lock(mutex_);
Expand All @@ -341,34 +387,11 @@ void Worker::JoinThread() {
thread_joined_ = true;

env()->remove_sub_worker_context(this);

if (thread_exit_async_) {
env()->CloseHandle(thread_exit_async_.release(), [](uv_async_t* async) {
delete async;
});

if (scheduled_on_thread_stopped_)
OnThreadStopped();
}
OnThreadStopped();
on_thread_finished_.Uninstall();
}

void Worker::OnThreadStopped() {
{
Mutex::ScopedLock lock(mutex_);
scheduled_on_thread_stopped_ = false;

Debug(this, "Worker %llu thread stopped", thread_id_);

{
Mutex::ScopedLock stopped_lock(stopped_mutex_);
CHECK(stopped_);
}

parent_port_ = nullptr;
}

JoinThread();

{
HandleScope handle_scope(env()->isolate());
Context::Scope context_scope(env()->context());
Expand All @@ -391,7 +414,7 @@ Worker::~Worker() {
Mutex::ScopedLock lock(mutex_);
JoinThread();

CHECK(stopped_);
CHECK(thread_stopper_.IsStopped());
CHECK(thread_joined_);

// This has most likely already happened within the worker thread -- this
Expand Down Expand Up @@ -480,16 +503,15 @@ void Worker::StartThread(const FunctionCallbackInfo<Value>& args) {
Mutex::ScopedLock lock(w->mutex_);

w->env()->add_sub_worker_context(w);
w->stopped_ = false;
w->thread_joined_ = false;
w->thread_stopper_.SetStopped(false);

w->thread_exit_async_.reset(new uv_async_t);
w->thread_exit_async_->data = w;
CHECK_EQ(uv_async_init(w->env()->event_loop(),
w->thread_exit_async_.get(),
[](uv_async_t* handle) {
static_cast<Worker*>(handle->data)->OnThreadStopped();
}), 0);
w->on_thread_finished_.Install(w->env(), w, [](uv_async_t* handle) {
Worker* w_ = static_cast<Worker*>(handle->data);
CHECK(w_->thread_stopper_.IsStopped());
w_->parent_port_ = nullptr;
w_->JoinThread();
});

uv_thread_options_t thread_options;
thread_options.flags = UV_THREAD_HAS_STACK_SIZE;
Expand All @@ -505,9 +527,7 @@ void Worker::StartThread(const FunctionCallbackInfo<Value>& args) {
w->Run();

Mutex::ScopedLock lock(w->mutex_);
CHECK(w->thread_exit_async_);
w->scheduled_on_thread_stopped_ = true;
uv_async_send(w->thread_exit_async_.get());
w->on_thread_finished_.Stop();
}, static_cast<void*>(w)), 0);
}

Expand All @@ -523,28 +543,23 @@ void Worker::StopThread(const FunctionCallbackInfo<Value>& args) {
void Worker::Ref(const FunctionCallbackInfo<Value>& args) {
Worker* w;
ASSIGN_OR_RETURN_UNWRAP(&w, args.This());
if (w->thread_exit_async_)
uv_ref(reinterpret_cast<uv_handle_t*>(w->thread_exit_async_.get()));
uv_ref(reinterpret_cast<uv_handle_t*>(w->on_thread_finished_.GetHandle()));
}

void Worker::Unref(const FunctionCallbackInfo<Value>& args) {
Worker* w;
ASSIGN_OR_RETURN_UNWRAP(&w, args.This());
if (w->thread_exit_async_)
uv_unref(reinterpret_cast<uv_handle_t*>(w->thread_exit_async_.get()));
uv_unref(reinterpret_cast<uv_handle_t*>(w->on_thread_finished_.GetHandle()));
}

void Worker::Exit(int code) {
Mutex::ScopedLock lock(mutex_);
Mutex::ScopedLock stopped_lock(stopped_mutex_);

Debug(this, "Worker %llu called Exit(%d)", thread_id_, code);

if (!stopped_) {
stopped_ = true;
if (!thread_stopper_.IsStopped()) {
exit_code_ = code;
if (child_port_ != nullptr)
child_port_->StopEventLoop();
Debug(this, "Received StopEventLoop request");
thread_stopper_.Stop();
if (isolate_ != nullptr)
isolate_->TerminateExecution();
}
Expand Down
39 changes: 26 additions & 13 deletions src/node_worker.h
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Original file line number Diff line number Diff line change
Expand Up @@ -3,14 +3,35 @@

#if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

#include "node_messaging.h"
#include <unordered_map>
#include "node_messaging.h"
#include "uv.h"

namespace node {
namespace worker {

class WorkerThreadData;

class AsyncRequest : public MemoryRetainer {
public:
AsyncRequest() : stop_(true) {}
void Install(Environment* env, void* data, uv_async_cb target);
void Uninstall();
void Stop();
void SetStopped(bool flag);
bool IsStopped();
uv_async_t* GetHandle();
void MemoryInfo(MemoryTracker* tracker) const override;
SET_MEMORY_INFO_NAME(AsyncRequest)
SET_SELF_SIZE(AsyncRequest)

private:
Environment* env_;
uv_async_t* async_ = nullptr;
mutable Mutex mutex_;
bool stop_ = true;
};

// A worker thread, as represented in its parent thread.
class Worker : public AsyncWrap {
public:
Expand All @@ -34,14 +55,13 @@ class Worker : public AsyncWrap {
tracker->TrackFieldWithSize(
"isolate_data", sizeof(IsolateData), "IsolateData");
tracker->TrackFieldWithSize("env", sizeof(Environment), "Environment");
tracker->TrackField("thread_exit_async", *thread_exit_async_);
tracker->TrackField("parent_port", parent_port_);
}

SET_MEMORY_INFO_NAME(Worker)
SET_SELF_SIZE(Worker)

bool is_stopped() const;
bool is_stopped();

static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static void StartThread(const v8::FunctionCallbackInfo<v8::Value>& args);
Expand All @@ -67,16 +87,6 @@ class Worker : public AsyncWrap {
// This mutex protects access to all variables listed below it.
mutable Mutex mutex_;

// Currently only used for telling the parent thread that the child
// thread exited.
std::unique_ptr<uv_async_t> thread_exit_async_;
bool scheduled_on_thread_stopped_ = false;

// This mutex only protects stopped_. If both locks are acquired, this needs
// to be the latter one.
mutable Mutex stopped_mutex_;
bool stopped_ = true;

bool thread_joined_ = true;
int exit_code_ = 0;
uint64_t thread_id_ = -1;
Expand All @@ -96,6 +106,9 @@ class Worker : public AsyncWrap {
// instance refers to it via its [kPort] property.
MessagePort* parent_port_ = nullptr;

AsyncRequest thread_stopper_;
AsyncRequest on_thread_finished_;

friend class WorkerThreadData;
};

Expand Down

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