channels.hpp

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/*
 
Copyright 2025 Matthew Tolman
 
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
 
   http://www.apache.org/licenses/LICENSE-2.0
 
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
 
*/
 
#pragma once
 
#ifndef MTCORE_THREAD_CHANNELS_HPP
#define MTCORE_THREAD_CHANNELS_HPP
 
#include "mtcore/colls/queue.hpp"
#include "mtcore_thread/core.hpp"
#include "mtcore_thread/traits.hpp"
 
#include <array>
#include <condition_variable>
#include <mutex>
#include <thread>

namespace mtcore::thread {
  enum class ChannelSendBlockErrors {
    CHANNEL_CLOSED,
  };
 
  static_assert(has_closed_error<ChannelSendBlockErrors>);

  enum class ChannelTrySendErrors {
    CHANNEL_CLOSED,
    COULD_NOT_LOCK,
    NO_ROOM,
  };
 
  static_assert(has_closed_error<ChannelTrySendErrors>);

  enum class ChannelSendBeforeErrors {
    CHANNEL_CLOSED,
    TIMEOUT,
  };
  static_assert(has_closed_error<ChannelSendBeforeErrors>);
 
  static_assert(static_cast<int>(ChannelTrySendErrors::CHANNEL_CLOSED) ==
                  static_cast<int>(ChannelSendBlockErrors::CHANNEL_CLOSED),
                "MISMATCHED CLOSED ERROR");
  static_assert(static_cast<int>(ChannelSendBeforeErrors::CHANNEL_CLOSED) ==
                  static_cast<int>(ChannelSendBlockErrors::CHANNEL_CLOSED),
                "MISMATCHED CLOSED ERROR");

  enum class ChannelTryReceiveErrors {
    COULD_NOT_LOCK,
    MESSAGE_NOT_READY,
  };

  enum class ChannelReceiveBeforeErrors {
    TIMEOUT,
  };

  template<typename T, size_t Size = 1>
  struct Channel {
    static_assert(Size > 0, "CANNOT HAVE UNBUFFERED THREAD-BASED CHANNELS");
 
  private:
    std::timed_mutex channelMux           = {};
    std::condition_variable_any read_cond = {};
    std::condition_variable_any send_cond = {};
    FixedQueue<T, Size> q                 = {};
    bool closed                           = false;
 
  public:
    using Message = T;

    void close() {
      auto lock = std::unique_lock(channelMux);
      closed    = true;
      read_cond.notify_all();
      send_cond.notify_all();
    }

    [[nodiscard]] Result<void, ChannelTrySendErrors> try_send(const T &msg) {
      auto lock = std::unique_lock(channelMux, std::try_to_lock_t{});
 
      if (!lock.owns_lock()) {
        return error(ChannelTrySendErrors::COULD_NOT_LOCK);
      }
 
      if (q.is_full()) {
        return error(ChannelTrySendErrors::NO_ROOM);
      }
 
      ensure(lock.owns_lock(), "DID NOT LOCK!");
      if (sendImpl(msg).is_error()) {
        return error(ChannelTrySendErrors::CHANNEL_CLOSED);
      }
      return success();
    }

    [[nodiscard]] Result<void, ChannelSendBlockErrors> send_block(const T &msg) {
      auto lock = std::unique_lock(channelMux);
      while (!closed && q.is_full()) {
        send_cond.wait(lock);
      }
 
      ensure(lock.owns_lock(), "DID NOT LOCK!");
      return sendImpl(msg);
    }

    template<typename Clock = std::chrono::steady_clock>
    [[nodiscard]] Result<void, ChannelSendBeforeErrors> send_before(const T &msg,
                                                                    const std::chrono::time_point<Clock> &when) {
      auto lock = std::unique_lock(channelMux, when);
 
      if (!lock.owns_lock()) {
        return error(ChannelSendBeforeErrors::TIMEOUT);
      }
 
      while (!closed && q.is_full()) {
        if (send_cond.wait_until(lock, when) == std::cv_status::timeout) {
          return error(ChannelSendBeforeErrors::TIMEOUT);
        }
      }
 
      ensure(lock.owns_lock(), "DID NOT LOCK!");
      if (sendImpl(msg).is_error()) {
        return error(ChannelSendBeforeErrors::CHANNEL_CLOSED);
      }
      return success();
    }

    [[nodiscard]] Result<Optional<T>, ChannelTryReceiveErrors> try_receive() {
      auto lock = std::unique_lock(channelMux, std::try_to_lock_t{});
 
      if (!lock.owns_lock()) {
        return error(ChannelTryReceiveErrors::COULD_NOT_LOCK);
      }
 
      if (q.is_empty()) {
        if (closed) {
          return readImpl();
        }
        return error(ChannelTryReceiveErrors::MESSAGE_NOT_READY);
      }
 
      ensure(lock.owns_lock(), "DID NOT LOCK!");
      return readImpl();
    }

    [[nodiscard]] Optional<Message> receive_block() {
      auto lock = std::unique_lock(channelMux);
 
      while (!closed && q.is_empty()) {
        read_cond.wait(lock);
      }
 
      ensure(lock.owns_lock(), "DID NOT LOCK");
      return readImpl();
    }

    template<typename Clock>
    [[nodiscard]] Result<Optional<T>, ChannelReceiveBeforeErrors>
    receive_before(const std::chrono::time_point<Clock> &when) {
      auto lock = std::unique_lock(channelMux, when);
 
      if (!lock.owns_lock()) {
        return error(ChannelReceiveBeforeErrors::TIMEOUT);
      }
 
      while (!closed && q.is_empty()) {
        if (read_cond.wait_until(lock, when) == std::cv_status::timeout) {
          return error(ChannelReceiveBeforeErrors::TIMEOUT);
        }
      }
 
      ensure(lock.owns_lock(), "DID NOT LOCK");
      return readImpl();
    }
 
  private:
    Result<void, ChannelSendBlockErrors> sendImpl(const T &msg) {
      if (closed) {
        return error(ChannelSendBlockErrors::CHANNEL_CLOSED);
      }
 
      ensure(!q.is_full(), "CANNOT SEND TO FULL BUFFER");
      ensure(q.push(msg).is_success());
      read_cond.notify_one();
      return success();
    }
 
    Optional<T> readImpl() {
      if (closed && q.is_empty()) {
        return nullopt;
      }
      ensure(!q.is_empty(), "CANNOT READ FROM EMPTY BUFFER");
      send_cond.notify_one();
      return q.pop();
    }
  };
  static_assert(is_channel_like<Channel<int, 1>>, "Channel<int, 1> not send/receive");
  static_assert(is_channel_like<Channel<int>>, "Channel<int> not channel-like");
}  // namespace mtcore::thread
 
#endif  // MTCORE_THREAD_CHANNELS_HPP