node_messaging.h

#ifndef SRC_NODE_MESSAGING_H_
#define SRC_NODE_MESSAGING_H_

#if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS

#include "env.h"
#include "node_mutex.h"
#include <list>
#include <memory>

namespace node {
namespace worker {

class MessagePortData;
class MessagePort;

// Represents a single communication message.
class Message {
 public:
  explicit Message(MallocedBuffer<char>&& payload = MallocedBuffer<char>());

  Message(Message&& other) = default;
  Message& operator=(Message&& other) = default;
  Message& operator=(const Message&) = delete;
  Message(const Message&) = delete;

  // Deserialize the contained JS value. May only be called once, and only
  // after Serialize() has been called (e.g. by another thread).
  v8::MaybeLocal<v8::Value> Deserialize(Environment* env,
                                        v8::Local<v8::Context> context);

  // Serialize a JS value, and optionally transfer objects, into this message.
  // The Message object retains ownership of all transferred objects until
  // deserialization.
  v8::Maybe<bool> Serialize(Environment* env,
                            v8::Local<v8::Context> context,
                            v8::Local<v8::Value> input,
                            v8::Local<v8::Value> transfer_list);

  // Internal method of Message that is called once serialization finishes
  // and that transfers ownership of `data` to this message.
  void AddMessagePort(std::unique_ptr<MessagePortData>&& data);

 private:
  MallocedBuffer<char> main_message_buf_;
  std::vector<MallocedBuffer<char>> array_buffer_contents_;
  std::vector<std::unique_ptr<MessagePortData>> message_ports_;

  friend class MessagePort;
};

// This contains all data for a `MessagePort` instance that is not tied to
// a specific Environment/Isolate/event loop, for easier transfer between those.
class MessagePortData {
 public:
  explicit MessagePortData(MessagePort* owner);
  ~MessagePortData();

  MessagePortData(MessagePortData&& other) = delete;
  MessagePortData& operator=(MessagePortData&& other) = delete;
  MessagePortData(const MessagePortData& other) = delete;
  MessagePortData& operator=(const MessagePortData& other) = delete;

  // Add a message to the incoming queue and notify the receiver.
  // This may be called from any thread.
  void AddToIncomingQueue(Message&& message);

  // Returns true if and only this MessagePort is currently not entangled
  // with another message port.
  bool IsSiblingClosed() const;

  // Turns `a` and `b` into siblings, i.e. connects the sending side of one
  // to the receiving side of the other. This is not thread-safe.
  static void Entangle(MessagePortData* a, MessagePortData* b);

  // Removes any possible sibling. This is thread-safe (it acquires both
  // `sibling_mutex_` and `mutex_`), and has to be because it is called once
  // the corresponding JS handle handle wants to close
  // which can happen on either side of a worker.
  void Disentangle();

 private:
  // After disentangling this message port, the owner handle (if any)
  // is asynchronously triggered, so that it can close down naturally.
  void PingOwnerAfterDisentanglement();

  // This mutex protects all fields below it, with the exception of
  // sibling_.
  mutable Mutex mutex_;
  bool receiving_messages_ = false;
  std::list<Message> incoming_messages_;
  MessagePort* owner_ = nullptr;
  // This mutex protects the sibling_ field and is shared between two entangled
  // MessagePorts. If both mutexes are acquired, this one needs to be
  // acquired first.
  std::shared_ptr<Mutex> sibling_mutex_ = std::make_shared<Mutex>();
  MessagePortData* sibling_ = nullptr;

  friend class MessagePort;
};

// A message port that receives messages from other threads, including
// the uv_async_t handle that is used to notify the current event loop of
// new incoming messages.
class MessagePort : public HandleWrap {
 public:
  // Create a new MessagePort. The `context` argument specifies the Context
  // instance that is used for creating the values emitted from this port.
  MessagePort(Environment* env,
              v8::Local<v8::Context> context,
              v8::Local<v8::Object> wrap);
  ~MessagePort();

  // Create a new message port instance, optionally over an existing
  // `MessagePortData` object.
  static MessagePort* New(Environment* env,
                          v8::Local<v8::Context> context,
                          std::unique_ptr<MessagePortData> data = nullptr);

  // Send a message, i.e. deliver it into the sibling's incoming queue.
  // If there is no sibling, i.e. this port is closed,
  // this message is silently discarded.
  void Send(Message&& message);
  void Send(const v8::FunctionCallbackInfo<v8::Value>& args);
  // Deliver a single message into this port's incoming queue.
  void AddToIncomingQueue(Message&& message);

  // Start processing messages on this port as a receiving end.
  void Start();
  // Stop processing messages on this port as a receiving end.
  void Stop();

  static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
  static void PostMessage(const v8::FunctionCallbackInfo<v8::Value>& args);
  static void Start(const v8::FunctionCallbackInfo<v8::Value>& args);
  static void Stop(const v8::FunctionCallbackInfo<v8::Value>& args);

  // Turns `a` and `b` into siblings, i.e. connects the sending side of one
  // to the receiving side of the other. This is not thread-safe.
  static void Entangle(MessagePort* a, MessagePort* b);
  static void Entangle(MessagePort* a, MessagePortData* b);

  // Detach this port's data for transferring. After this, the MessagePortData
  // is no longer associated with this handle, although it can still receive
  // messages.
  std::unique_ptr<MessagePortData> Detach();

  bool IsSiblingClosed() const;

  size_t self_size() const override;

 private:
  void OnClose() override;
  void OnMessage();
  void TriggerAsync();
  inline uv_async_t* async();

  std::unique_ptr<MessagePortData> data_ = nullptr;

  friend class MessagePortData;
};

v8::MaybeLocal<v8::Function> GetMessagePortConstructor(
    Environment* env, v8::Local<v8::Context> context);

}  // namespace worker
}  // namespace node

#endif  // defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS


#endif  // SRC_NODE_MESSAGING_H_