broadcaster.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.
 
*/
 
#ifndef MTCORE_THREAD_BROADCAST_HPP
#define MTCORE_THREAD_BROADCAST_HPP
 
#include "mtcore/colls/gen_list.hpp"
#include "mtcore_thread/arc.hpp"
#include "mtcore_thread/channels.hpp"
#include "mtcore_thread/inbox.hpp"


namespace mtcore::thread {
  enum class BroadcastSubscribeError { CHANNEL_CLOSED, ALLOCATION_FAILED, CANNOT_ACQUIRE };

  template<typename T>
  struct BroadcastSubscription {
    Arc<Inbox<T>> inbox;
 
    Result<void, AllocationError> init(Allocator &alloc) {
      if (auto inboxRes = inbox.init(alloc); inboxRes.is_error()) {
        return inboxRes.error();
      }
      return inbox->init(alloc);
    }
 
    Optional<T> receive_block() {
      ensure(inbox.valid(), "SUBSCRIPTION IS NOT INITIALIZED!");
      return inbox->receive_block();
    }
 
    void deinit(Allocator &alloc) {
      if (inbox.valid()) {
        inbox->close();
      }
      inbox.release(alloc);
    }
  };

  template<typename T>
  struct broadcaster {
    GenList<BroadcastSubscription<T>> channels;
    std::mutex mux;
    bool closed = false;

    Result<void, AllocationError> init(Allocator &alloc, size_t initCapacity = 64) {
      return channels.init(alloc, initCapacity);
    }

    Result<void, ChannelSendBlockErrors> send_block(Allocator &alloc, const T &msg) {
      // We need the lock since we'll be iterating and removing stuff
      auto l = std::unique_lock{mux};
 
      if (closed) {
        return error(ChannelSendBlockErrors::CHANNEL_CLOSED);
      }
 
      Handle handle;
      auto iter = channels.handles();
      while (iter.next().copy_if_present(handle)) {
        auto &e = channels[handle];
        if (e.inbox.valid()) {
          if (auto res = e.inbox->send_block(alloc, msg); res.is_error()) {
            // If we failed allocation, try a non-allocating send
            if (res.error().code == ChannelGrowSendBlockErrors::ALLOCATION_FAILED) {
              // We can still fail if our channel is closed. In this case, remove the channel
              if (auto res2 = e.inbox->send_block(msg); res2.is_error()) {
                e.inbox.release(alloc);
                channels.remove(handle);
              }
            }
            // otherwise, our channel is closed, just remove the channel
            else {
              e.inbox.release(alloc);
              channels.remove(handle);
            }
          }
        }
        else {
          // clean up and remove the channel
          e.deinit(alloc);
          channels.remove(handle);
        }
      }
      return success();
    }

    Result<BroadcastSubscription<T>, BroadcastSubscribeError> subscribe(Allocator &alloc) {
      BroadcastSubscription<T> sub;
      if (auto subRes = sub.init(alloc); subRes.is_error()) {
        return error(BroadcastSubscribeError::ALLOCATION_FAILED);
      }
 
      // We need the lock since we'll be removing stuff
      {
        auto l = std::unique_lock{mux};
        if (closed) {
          sub.deinit(alloc);
          return error(BroadcastSubscribeError::CHANNEL_CLOSED);
        }
 
        if (auto addRes = channels.add(alloc, sub); addRes.is_error()) {
          sub.deinit(alloc);
          return error(BroadcastSubscribeError::ALLOCATION_FAILED);
        }
      }
      auto acquireRes = sub.inbox.acquire(alloc);
      if (acquireRes.is_error()) {
        sub.deinit(alloc);
        return error(BroadcastSubscribeError::CANNOT_ACQUIRE);
      }
      return BroadcastSubscription<T>{acquireRes.value()};
    }

    void close() {
      auto l = std::unique_lock{mux};
      closed = true;
      BroadcastSubscription<T> cur;
      auto iter = channels.iter();
      while (iter.next().copy_if_present(cur)) {
        if (cur.inbox.valid()) {
          cur.inbox->close();
        }
      }
    }

    void deinit(Allocator &alloc) {
      auto l = std::unique_lock{mux};
      closed = true;
      BroadcastSubscription<T> cur;
      auto iter = channels.iter();
      while (iter.next().copy_if_present(cur)) {
        cur.deinit(alloc);
      }
      channels.deinit(alloc);
    }
  };
 
}  // namespace mtcore::thread
 
#endif  // MTCORE_THREAD_BROADCAST_HPP