#include <torch/csrc/distributed/rpc/tensorpipe_agent.h>

#include <limits>

#include <fmt/format.h>
#include <torch/csrc/distributed/rpc/request_callback_impl.h>
#include <torch/csrc/distributed/rpc/utils.h>

namespace torch {
namespace distributed {
namespace rpc {

namespace {

// An environment variable along the lines of GLOO_ and NCCL_SOCKET_IFNAME that
// allows the user to specify a device to bind to, instead of binding to the
// address that the hostname resolves to.
const std::string kSocketIfnameEnvVar = "TP_SOCKET_IFNAME";
const std::string kDefaultUvAddress = "127.0.0.1";

constexpr long kToMilliseconds = 1000;

const std::string kGilAverageWaitTime = "agent.gil_average_wait_time_us";
const std::string kThreadPoolSize = "agent.thread_pool_size";
const std::string kNumIdleThreads = "agent.num_idle_threads";
const std::string kClientActiveCalls = "agent.client_active_calls";
const std::string kServerActiveCalls = "agent.server_active_calls";
const std::string kServerActiveAsyncCalls = "agent.server_active_async_calls";
const std::string kRpcTimeoutErrorStr =
    "RPC ran for more than set timeout ({} ms) and will now be marked with an error";

} // namespace

C10_DEFINE_REGISTRY(TensorPipeTransportRegistry, TransportRegistration);

C10_DEFINE_REGISTRY(TensorPipeChannelRegistry, ChannelRegistration);

std::string TensorPipeAgent::guessUvAddress(
    tensorpipe::transport::uv::Context& uvContext) {
  tensorpipe::Error error;
  std::string uvAddress;
  char* ifnameEnv = std::getenv(kSocketIfnameEnvVar.c_str());
  if (ifnameEnv != nullptr) {
    std::tie(error, uvAddress) = uvContext.lookupAddrForIface(ifnameEnv);
    if (error) {
      LOG(WARNING) << "Failed to look up the IP address for interface "
                   << ifnameEnv << " (" << error.what() << "), defaulting to "
                   << kDefaultUvAddress;
      uvAddress = kDefaultUvAddress;
    }
  } else {
    std::tie(error, uvAddress) = uvContext.lookupAddrForHostname();
    if (error) {
      LOG(WARNING) << "Failed to look up the IP address for the hostname ("
                   << error.what() << "), defaulting to " << kDefaultUvAddress;
      uvAddress = kDefaultUvAddress;
    }
  }
  return uvAddress;
}

namespace {

// These priorities instruct TensorPipe on which transport/channel to pick
// during handshake. Higher priorities will take precedence over lower ones.
// The transport with lowest priority will be the one used to bootstrap pipes.

constexpr int64_t kShmTransportPriority = 100;
// The UV transport just uses TCP and should work everywhere, thus keep it last.
constexpr int64_t kUvTransportPriority = 0;

constexpr int64_t kCmaChannelPriority = 200;
constexpr int64_t kMultiplexedUvChannelPriority = 100;
// The basic channel reuses a transport as a channel, and is thus our fallback.
constexpr int64_t kBasicChannelPriority = 0;

std::unique_ptr<TransportRegistration> makeUvTransport() {
  auto context = std::make_shared<tensorpipe::transport::uv::Context>();
  std::string address = TensorPipeAgent::guessUvAddress(*context);
  return std::make_unique<TransportRegistration>(TransportRegistration{
      std::move(context), kUvTransportPriority, std::move(address)});
}

// The UV transport is implemented using standard TCP connections. It leverages
// libuv (https://github.com/libuv/libuv) in order to be cross-platform.
C10_REGISTER_CREATOR(TensorPipeTransportRegistry, uv, makeUvTransport);

#ifdef TP_ENABLE_SHM

std::unique_ptr<TransportRegistration> makeShmTransport() {
  auto context = std::make_shared<tensorpipe::transport::shm::Context>();
  std::string address = TensorPipeAgent::createUniqueShmAddr();
  return std::make_unique<TransportRegistration>(TransportRegistration{
      std::move(context), kShmTransportPriority, std::move(address)});
}

// The SHM implements connections using ringbuffers residing in anonymous shared
// memory (plus UNIX domain sockets to bootstrap the connection and exchange
// file descriptors). It is Linux-only due to some advanced features (O_TMPFILE,
// eventfd, ...).
C10_REGISTER_CREATOR(TensorPipeTransportRegistry, shm, makeShmTransport);

#endif

std::unique_ptr<ChannelRegistration> makeBasicChannel() {
  auto context = std::make_shared<tensorpipe::channel::basic::Context>();
  return std::make_unique<ChannelRegistration>(
      ChannelRegistration{std::move(context), kBasicChannelPriority});
}

// The basic channel is just a straightforward adapter wrapper that allows any
// transport to be used as a channel.
C10_REGISTER_CREATOR(TensorPipeChannelRegistry, basic, makeBasicChannel);

#ifdef TP_ENABLE_CMA

std::unique_ptr<ChannelRegistration> makeCmaChannel() {
  auto context = std::make_shared<tensorpipe::channel::cma::Context>();
  return std::make_unique<ChannelRegistration>(
      ChannelRegistration{std::move(context), kCmaChannelPriority});
}

// The CMA channel uses the Linux cross-memory attach syscalls (process_vm_readv
// and _writev), which allow one process to access the private memory of another
// process (as long as they belong to the same user and other security
// constraints are satisfied). It does, more or less, what GDB does when it's
// attached to a running process.
C10_REGISTER_CREATOR(TensorPipeChannelRegistry, cma, makeCmaChannel);

#endif

constexpr static int kNumUvThreads = 16;

std::unique_ptr<ChannelRegistration> makeMultiplexedUvChannel() {
  std::vector<std::shared_ptr<tensorpipe::transport::Context>> contexts;
  std::vector<std::shared_ptr<tensorpipe::transport::Listener>> listeners;
  for (int laneIdx = 0; laneIdx < kNumUvThreads; ++laneIdx) {
    auto context = std::make_shared<tensorpipe::transport::uv::Context>();
    std::string address = TensorPipeAgent::guessUvAddress(*context);
    contexts.push_back(std::move(context));
    listeners.push_back(contexts.back()->listen(address));
  }
  auto context = std::make_shared<tensorpipe::channel::mpt::Context>(
      std::move(contexts), std::move(listeners));
  return std::make_unique<ChannelRegistration>(
      ChannelRegistration{std::move(context), kMultiplexedUvChannelPriority});
}

// The multiplexed UV channel encapsulates multiple UV transports (each with its
// own event loop thread). Each channel will, in turn, contain multiple UV
// connections, one for each of those contexts. When sending a tensor, its data
// is split in equal chunks and each chunks is sent on a different connection
// and thus driven by a different thread. This is needed to reach very high
// bandwidths.
C10_REGISTER_CREATOR(
    TensorPipeChannelRegistry,
    mpt_uv,
    makeMultiplexedUvChannel);

} // namespace

//////////////////////////  MetricsTracker  /////////////////////////////////

TensorPipeAgent::TimeSeriesMetricsTracker::TimeSeriesMetricsTracker(
    uint64_t currentSum,
    uint64_t currentCount)
    : currentSum_(currentSum), currentCount_(currentCount) {}

void TensorPipeAgent::TimeSeriesMetricsTracker::addData(uint64_t dataPoint) {
  currentSum_ += dataPoint;
  ++currentCount_;
}

float TensorPipeAgent::TimeSeriesMetricsTracker::computeAverage() const {
  return currentCount_ == 0 ? 0 : currentSum_ / (float)currentCount_;
}

////////////////////////  TensorpipeRpcAgent  /////////////////////////////////

void TensorPipeAgent::collectNames() {
  const worker_id_t selfId = workerInfo_.id_;
  const std::string& selfName = workerInfo_.name_;

  std::vector<uint8_t> selfNameVector(
      (uint8_t*)selfName.c_str(),
      (uint8_t*)selfName.c_str() + selfName.length());
  rankToNameStore_.set(c10::to_string(selfId), selfNameVector);

  workerIdToInfo_.emplace(selfId, WorkerInfo(selfName, selfId));
  workerNameToInfo_.emplace(selfName, WorkerInfo(selfName, selfId));
  for (worker_id_t workerId = 0; workerId < worldSize_; ++workerId) {
    if (workerId == selfId) {
      continue;
    }
    std::vector<uint8_t> workerNameVector =
        rankToNameStore_.get(c10::to_string(workerId));
    std::string workerName(
        (char*)workerNameVector.data(), workerNameVector.size());

    TORCH_CHECK(
        workerNameToInfo_.find(workerName) == workerNameToInfo_.end(),
        "RPC worker name ",
        workerName,
        " is not unique.");

    workerIdToInfo_.emplace(workerId, WorkerInfo(workerName, workerId));
    workerNameToInfo_.emplace(workerName, WorkerInfo(workerName, workerId));
  }
}

TensorPipeAgent::TensorPipeAgent(
    const std::shared_ptr<::c10d::Store>& store,
    std::string selfName,
    worker_id_t selfId,
    int worldSize,
    std::shared_ptr<c10d::ProcessGroup> processGroup,
    TensorPipeRpcBackendOptions opts)
    : RpcAgent(
          WorkerInfo(std::move(selfName), selfId),
          std::make_unique<RequestCallbackImpl>(),
          std::chrono::milliseconds(
              (long)(opts.rpcTimeoutSeconds * kToMilliseconds))),
      opts_(std::move(opts)),
      threadPool_(opts_.numWorkerThreads),
      context_(std::make_shared<tensorpipe::Context>(
          tensorpipe::ContextOptions().name(workerInfo_.name_))),
      rankToNameStore_("names", store),
      nameToAddressStore_("addrs", store),
      worldSize_(worldSize),
      processGroup_(std::move(processGroup)) {
  collectNames();

  // Initialize the time-series metrics tracking map
  timeSeriesMetrics_.emplace(kGilAverageWaitTime, TimeSeriesMetricsTracker());
}

TensorPipeAgent::~TensorPipeAgent() {
  VLOG(1) << "RPC agent for " << workerInfo_.name_ << " is being destroyed";
  shutdown();
}

void TensorPipeAgent::startImpl() {
  VLOG(1) << "RPC agent for " << workerInfo_.name_ << " is starting";

  std::vector<std::string> addresses;
  int lowestPriority = std::numeric_limits<int>::max();
  std::string lowestPriorityTransport;

  for (auto& key : TensorPipeTransportRegistry()->Keys()) {
    int64_t priority = -1;
    if (opts_.transports.has_value()) {
      auto iter =
          std::find(opts_.transports->begin(), opts_.transports->end(), key);
      if (iter == opts_.transports->end()) {
        continue;
      }
      // Assign priorities in reverse order of occurrence in the vector, so that
      // a transport that comes before another receives a higher priority.
      priority =
          opts_.transports->size() - 1 - (iter - opts_.transports->begin());
    }
    std::unique_ptr<TransportRegistration> reg =
        TensorPipeTransportRegistry()->Create(key);
    if (priority == -1) {
      priority = reg->priority;
    }
    if (priority < lowestPriority) {
      lowestPriority = priority;
      lowestPriorityTransport = key;
    }
    addresses.push_back(c10::str(key, "://", reg->address));
    context_->registerTransport(
        priority, std::move(key), std::move(reg->transport));
  }

  for (auto& key : TensorPipeChannelRegistry()->Keys()) {
    int64_t priority = -1;
    if (opts_.channels.has_value()) {
      auto iter =
          std::find(opts_.channels->begin(), opts_.channels->end(), key);
      if (iter == opts_.channels->end()) {
        continue;
      }
      // Assign priorities in reverse order of occurrence in the vector, so that
      // a channel that comes before another receives a higher priority.
      priority = opts_.channels->size() - 1 - (iter - opts_.channels->begin());
    }
    std::unique_ptr<ChannelRegistration> reg =
        TensorPipeChannelRegistry()->Create(key);
    if (priority == -1) {
      priority = reg->priority;
    }
    context_->registerChannel(
        priority, std::move(key), std::move(reg->channel));
  }

  listener_ = context_->listen(addresses);

  // Store our own url.
  const auto address = listener_->url(lowestPriorityTransport);
  const std::vector<uint8_t> selfAddrData(address.begin(), address.end());
  nameToAddressStore_.set(workerInfo_.name_, selfAddrData);

  VLOG(1) << "RPC agent for " << workerInfo_.name_ << " is using address "
          << address;

  for (const auto& p : workerNameToInfo_) {
    const auto& name = p.first;
    auto nodeAddrData = nameToAddressStore_.get(name);
    auto nodeAddrStr =
        std::string((const char*)nodeAddrData.data(), nodeAddrData.size());
    workerNameToURL_.insert({name, nodeAddrStr});
  }

  // Start the Timeout Thread
  timeoutThread_ = std::thread(&TensorPipeAgent::pollTimeoutRpcs, this);

  listener_->accept([this](
                        const tensorpipe::Error& error,
                        std::shared_ptr<tensorpipe::Pipe> pipe) {
    onListenerAccepted(error, pipe);
  });
}

void TensorPipeAgent::onListenerAccepted(
    const tensorpipe::Error& error,
    std::shared_ptr<tensorpipe::Pipe>& pipe) {
  if (error) {
    if (error.isOfType<tensorpipe::ListenerClosedError>() &&
        !rpcAgentRunning_.load()) {
      // This is expected.
    } else {
      LOG(WARNING) << "RPC agent for " << workerInfo_.name_
                   << " encountered error when accepting incoming pipe: "
                   << error.what();
    }
    return;
  }

  // Accept the next connection request
  listener_->accept([this](
                        const tensorpipe::Error& error,
                        std::shared_ptr<tensorpipe::Pipe> pipe) {
    onListenerAccepted(error, pipe);
  });

  VLOG(1) << "RPC agent for " << workerInfo_.name_
          << " accepted incoming pipe from " << pipe->getRemoteName();

  // Arm for server read
  respond(pipe);
}

void TensorPipeAgent::pipeRead(
    const std::shared_ptr<tensorpipe::Pipe>& pipe,
    std::function<void(const tensorpipe::Error&, Message&&)> fn) {
  pipe->readDescriptor([fn{std::move(fn)}, pipe](
                           const tensorpipe::Error& error,
                           tensorpipe::Message tpMessage) mutable {
    if (error) {
      fn(error, Message());
      return;
    }

    TensorpipeReadBuffers tpBuffers = tensorpipeAllocate(tpMessage);

    pipe->read(
        std::move(tpMessage),
        [tpBuffers{
             std::make_shared<TensorpipeReadBuffers>(std::move(tpBuffers))},
         fn{std::move(fn)}](
            const tensorpipe::Error& error,
            tensorpipe::Message tpMessage) mutable {
          if (error) {
            fn(error, Message());
            return;
          }

          // FIXME This does some unpickling, which could be a bit expensive:
          // perhaps it would be best to perform it inside the worker threads?
          Message rpcMessage = tensorpipeDeserialize(
              std::move(tpMessage), std::move(*tpBuffers));

          fn(error, std::move(rpcMessage));
        });
  });
}

void TensorPipeAgent::pipeWrite(
    const std::shared_ptr<tensorpipe::Pipe>& pipe,
    Message&& rpcMessage,
    std::function<void(const tensorpipe::Error&)> fn) {
  tensorpipe::Message tpMessage;
  TensorpipeWriteBuffers tpBuffers;
  std::tie(tpMessage, tpBuffers) = tensorpipeSerialize(std::move(rpcMessage));
  pipe->write(
      std::move(tpMessage),
      [tpBuffers{
           std::make_shared<TensorpipeWriteBuffers>(std::move(tpBuffers))},
       fn{std::move(fn)}](
          const tensorpipe::Error& error, tensorpipe::Message /* unused */) {
        fn(error);
      });
}

void TensorPipeAgent::sendCompletedResponseMessage(
    std::shared_ptr<tensorpipe::Pipe>& pipe,
    std::shared_ptr<FutureMessage>& futureResponseMessage,
    uint64_t messageId) {
  if (!rpcAgentRunning_.load()) {
    LOG(WARNING) << "RPC agent for " << workerInfo_.name_
                 << " won't send response to request #" << messageId << " to "
                 << pipe->getRemoteName() << ", as the agent is shutting down";
    return;
  }

  VLOG(1) << "RPC agent for " << workerInfo_.name_
          << " is sending response to request #" << messageId << " to "
          << pipe->getRemoteName();

  const c10::optional<utils::FutureError> error =
      futureResponseMessage->error();
  Message&& responseMessage = std::move(*futureResponseMessage).moveValue();
  responseMessage.setId(messageId);
  if (!error) {
    for (const auto& tensor : responseMessage.tensors()) {
      if (!tensor.device().is_cpu()) {
        responseMessage = createExceptionResponse(
            c10::str(
                "TensorPipe RPC backend only supports CPU tensors, please ",
                "move your tensors to CPU before sending them over RPC. Found ",
                "tensor on device: ",
                tensor.device()),
            responseMessage.id());
        break;
      }
    }

    pipeWrite(
        pipe,
        std::move(responseMessage),
        [this, pipe, messageId](const tensorpipe::Error& error) {
          if (error) {
            LOG(WARNING)
                << "RPC agent for " << workerInfo_.name_
                << " encountered error when sending response to request #"
                << messageId << " to " << pipe->getRemoteName() << ": "
                << error.what();
            return;
          }

          VLOG(1) << "RPC agent for " << workerInfo_.name_
                  << " done sending response to request #" << messageId
                  << " to " << pipe->getRemoteName();
        });
  } else {
    pipeWrite(
        pipe,
        createExceptionResponse(error->what(), responseMessage.id()),
        [this, pipe, messageId](const tensorpipe::Error& error) {
          if (error) {
            LOG(WARNING)
                << "RPC agent for " << workerInfo_.name_
                << " encountered error when sending response to request #"
                << messageId << " to " << pipe->getRemoteName() << ": "
                << error.what();
            return;
          }

          VLOG(1) << "RPC agent for " << workerInfo_.name_
                  << " done sending response to request #" << messageId
                  << " to " << pipe->getRemoteName();
        });
  }
}

void TensorPipeAgent::respond(std::shared_ptr<tensorpipe::Pipe>& pipe) {
  pipeRead(
      pipe,
      [this, pipe](
          const tensorpipe::Error& error, Message&& requestMessage) mutable {
        if (error) {
          // FIXME This is not a correct way to check whether this error was
          // "intentionally" caused by the remote end shutting down. We should
          // find a better way, Perhaps sending an empty message?
          if ((error.isOfType<tensorpipe::PipeClosedError>() &&
               !rpcAgentRunning_.load()) ||
              error.isOfType<tensorpipe::transport::EOFError>()) {
            // This is expected.
          } else {
            LOG(WARNING)
                << "RPC agent for " << workerInfo_.name_
                << " encountered error when reading incoming request from "
                << pipe->getRemoteName() << ": " << error.what()
                << " (this is expected to happen during shutdown)";
          }
          return;
        }

        // Arm for next read
        respond(pipe);

        uint64_t messageId = requestMessage.id();
        increaseCallCount(serverActiveCalls_);

        VLOG(1) << "RPC agent for " << workerInfo_.name_
                << " received request #" << messageId << " from "
                << pipe->getRemoteName();

        // Defer user RPC UDF run to thread pool
        threadPool_.run([this,
                         pipe,
                         messageId,
                         requestMessage{std::move(requestMessage)}]() mutable {
          VLOG(1) << "RPC agent for " << workerInfo_.name_
                  << " is running request #" << messageId << " from "
                  << pipe->getRemoteName() << " in thread pool";

          std::shared_ptr<FutureMessage> futureResponseMessage;
          try {
            futureResponseMessage = cb_->operator()(requestMessage);
          } catch (const std::exception& e) {
            futureResponseMessage = std::make_shared<FutureMessage>();
            futureResponseMessage->setError(e.what());
          }

          // Shortcut if immediately done
          if (futureResponseMessage->completed()) {
            decreaseCallCount(serverActiveCalls_);
            sendCompletedResponseMessage(
                pipe, futureResponseMessage, messageId);
          } else {
            // Not complete yet
            increaseCallCount(serverActiveAsyncCalls_);
            futureResponseMessage->addCallback(
                [this, pipe, futureResponseMessage, messageId]() mutable {
                  decreaseCallCount(serverActiveCalls_);
                  decreaseCallCount(serverActiveAsyncCalls_);
                  sendCompletedResponseMessage(
                      pipe, futureResponseMessage, messageId);
                });
          }

          VLOG(1) << "RPC agent for " << workerInfo_.name_
                  << " done running request #" << messageId << " from "
                  << pipe->getRemoteName() << " in thread pool";
        });
      });
}

std::shared_ptr<FutureMessage> TensorPipeAgent::send(
    const WorkerInfo& toWorkerInfo,
    Message&& requestMessage,
    const float rpcTimeoutSeconds) {
  TORCH_CHECK(
      requestMessage.isRequest(),
      "TensorPipeAgent::send(..) is only for sending requests.");

  if (!rpcAgentRunning_.load()) {
    auto err = c10::str(
        "Node ",
        RpcAgent::getWorkerInfo().id_,
        "tried to send() a message of type ",
        requestMessage.type(),
        " but RPC is no longer running on this node.");
    throw std::runtime_error(err);
  }

  for (const auto& tensor : requestMessage.tensors()) {
    TORCH_CHECK(
        tensor.device().is_cpu(),
        "TensorPipe RPC backend only supports CPU tensors, please move your ",
        "tensors to CPU before sending them over RPC. Found tensor on device: ",
        tensor.device());
  }

  const auto& url = findWorkerURL(toWorkerInfo);

  std::unique_lock<std::mutex> lock(mutex_);

  // See if we already have a connection to this address or not
  auto it = connectedPipes_.find(toWorkerInfo.id_);
  if (it == connectedPipes_.end()) {
    std::tie(it, std::ignore) = connectedPipes_.emplace(
        toWorkerInfo.id_,
        ClientPipe(context_->connect(
            url, tensorpipe::PipeOptions().remoteName(toWorkerInfo.name_))));
  }
  ClientPipe& clientPipe = it->second;
  auto& pendingResponseMessage = clientPipe.pendingResponseMessage_;

  auto futureResponseMessage = std::make_shared<AtomicFutureMessage>();
  uint64_t messageId = nextMessageID_++;
  requestMessage.setId(messageId);
  pendingResponseMessage[messageId] = futureResponseMessage;

  lock.unlock();

  futureResponseMessage->futMsg.addCallback([this]() {
    TORCH_INTERNAL_ASSERT(
        this->threadPool_.inThreadPool(),
        "Future marked complete from outside the thread pool");
  });

  increaseCallCount(clientActiveCalls_);
  // Use the default RPC timeout if no timeout is specified for this send call
  auto timeout = rpcTimeoutSeconds == kUnsetRpcTimeout
      ? getRpcTimeout()
      : std::chrono::milliseconds(
            static_cast<int>(rpcTimeoutSeconds * kToMilliseconds));

  // We only add to the timeoutMap_ if the timeout is not 0. Per our
  // documentation, a user-provided timeout of 0 indicates the RPC should never
  // expire (infinite timeout), so there is no need to track it in the
  // timeoutMap_.
  if (timeout.count() != 0) {
    // Compute the expiration time for this message based on the timeout
    auto expirationTime = computeRpcMessageExpiryTime(timeout);

    // Add the Future to the right vector in the timeoutMap_
    {
      std::unique_lock<std::mutex> lock(timeoutMapMutex_);
      auto& timeoutFuturesVector = timeoutMap_[expirationTime];
      timeoutFuturesVector.emplace_back(futureResponseMessage, timeout);
    }
    timeoutThreadCV_.notify_one();
  }

  VLOG(1) << "RPC agent for " << workerInfo_.name_ << " is sending request #"
          << messageId << " to " << clientPipe.pipe_->getRemoteName();

  pipeWrite(
      clientPipe.pipe_,
      std::move(requestMessage),
      [this, &clientPipe, messageId](const tensorpipe::Error& error) mutable {
        if (error) {
          if (error.isOfType<tensorpipe::PipeClosedError>() &&
              !rpcAgentRunning_.load()) {
            // This is expected.
          } else {
            LOG(WARNING) << "RPC agent for " << workerInfo_.name_
                         << " encountered error when sending outgoing request #"
                         << messageId << " to "
                         << clientPipe.pipe_->getRemoteName() << ": "
                         << error.what();
          }
          auto pendingFutIt =
              clientPipe.pendingResponseMessage_.find(messageId);
          if (pendingFutIt != clientPipe.pendingResponseMessage_.end()) {
            markFutureWithError(pendingFutIt->second, error.what());
          }
          return;
        }

        VLOG(1) << "RPC agent for " << workerInfo_.name_ << " sent request #"
                << messageId << " to " << clientPipe.pipe_->getRemoteName();

        pipeRead(
            clientPipe.pipe_,
            [this, &clientPipe](
                const tensorpipe::Error& error, Message&& responseMessage) {
              if (error) {
                if (error.isOfType<tensorpipe::PipeClosedError>() &&
                    !rpcAgentRunning_.load()) {
                  // This is expected.
                } else {
                  LOG(WARNING)
                      << "RPC agent for " << workerInfo_.name_
                      << " encountered error when reading incoming response from "
                      << clientPipe.pipe_->getRemoteName() << ": "
                      << error.what();
                }
                // We may get garbage content in responseMessage upon error.
                // Flushing all future messages belonging to this pipe due to
                // error state.
                decltype(clientPipe.pendingResponseMessage_) pendingMsgs;
                {
                  std::lock_guard<std::mutex> lock(mutex_);
                  std::swap(clientPipe.pendingResponseMessage_, pendingMsgs);
                  clientPipe.readError_ = true;
                }
                std::string errorMsg = error.what();
                for (auto& p : pendingMsgs) {
                  markFutureWithError(std::move(p.second), errorMsg);
                }
                return;
              }

              // Identify future response message by message ID
              uint64_t messageId = responseMessage.id();

              VLOG(1) << "RPC agent for " << workerInfo_.name_
                      << " received response #" << messageId << " from "
                      << clientPipe.pipe_->getRemoteName();

              std::shared_ptr<AtomicFutureMessage> futureResponseMessage;
              {
                std::lock_guard<std::mutex> lock(mutex_);
                // A read error will lead all following callbacks to be
                // invoked with error, and shouldn't reach here.
                TORCH_INTERNAL_ASSERT(
                    !clientPipe.readError_, "Shouldn't in error state");
                auto it = clientPipe.pendingResponseMessage_.find(messageId);
                TORCH_INTERNAL_ASSERT(
                    it != clientPipe.pendingResponseMessage_.end(),
                    "message ID ",
                    messageId,
                    " is not recognized");
                futureResponseMessage = std::move(it->second);
                clientPipe.pendingResponseMessage_.erase(it);
              }

              if (responseMessage.type() == MessageType::EXCEPTION) {
                markFutureWithError(
                    std::move(futureResponseMessage),
                    std::string(
                        responseMessage.payload().begin(),
                        responseMessage.payload().end()));
              } else {
                markFutureAsComplete(
                    std::move(futureResponseMessage),
                    std::move(responseMessage));
              }
            });
      });

  return std::shared_ptr<FutureMessage>(
      futureResponseMessage, &futureResponseMessage->futMsg);
}

void TensorPipeAgent::pollTimeoutRpcs() {
  while (rpcAgentRunning_.load()) {
    std::unique_lock<std::mutex> lock(timeoutMapMutex_);

    // We sleep until the earliest expiring RPC in the timeoutMap_. We must
    // also ensure that we sleep while the map is empty, and we exit sleeping
    // if the RPC Agent has been shutdown.
    for (;;) {
      if (!rpcAgentRunning_.load()) {
        return;
      }

      if (!timeoutMap_.empty()) {
        steady_clock_time_point earliestTimeout = timeoutMap_.begin()->first;
        if (std::chrono::steady_clock::now() >= earliestTimeout) {
          break;
        }
        timeoutThreadCV_.wait_until(lock, earliestTimeout);
      } else {
        timeoutThreadCV_.wait(lock);
      }
    }

    // Move all these futures to a separate vector so we can process them
    // outside the lock.
    std::vector<std::pair<
        std::shared_ptr<AtomicFutureMessage>,
        std::chrono::milliseconds>>
        timedOutFutures = std::move(timeoutMap_.begin()->second);
    // We can safely remove this key from the timeoutMap_ since all these
    // futures will be processed.
    timeoutMap_.erase(timeoutMap_.begin());

    lock.unlock();

    // Set an error on futures added to the timedOutFutures vector. We do this
    // outside the lock to prevent potential lock-order-inversions by callbacks
    // triggered by the setError call.
    for (auto& futureTimeoutPair : timedOutFutures) {
      std::string errorMsg =
          fmt::format(kRpcTimeoutErrorStr, futureTimeoutPair.second.count());
      auto err = makeRPCError(errorMsg, RPCErrorType::TIMEOUT);
      markFutureWithError(std::move(futureTimeoutPair.first), std::move(err));
    }
  }
}

// TODO: Remove sync()
void TensorPipeAgent::sync() {
  VLOG(1) << "RPC agent for " << workerInfo_.name_ << " is syncing (no-op)";
}

// TODO: Remove join()
void TensorPipeAgent::join() {
  VLOG(1) << "RPC agent for " << workerInfo_.name_ << " is joining";
  // This method behaves like a barrier, as it can only return once all workers
  // have no more requests pending, including "nested" requests (triggered from
  // within the remote code of another call) and "follow-up" requests (triggered
  // from the callback of a future).
  while (true) {
    {
      std::unique_lock<std::mutex> lock(callCountMutex_);
      // It is enough to wait for there to be no more active client calls, since
      // each server call corresponds to a client call for some other worker.
      callCountCV_.wait(lock, [this] { return clientActiveCalls_ == 0; });
      // We'd like to immediately proceed with the allreduce, but it's a call
      // that may block for some time, as it waits for other workers to also
      // complete all their active client calls. While we call allreduce we must
      // hold the mutex, or else the count we send to other workers may get
      // stale (e.g., if some nested call happens in the meantime). But we can't
      // hold the lock for an indeterminately long time, as that would block
      // other operations (e.g., send). Thus we must release the lock and only
      // re-acquire it when all workers are ready to proceed with the allreduce.
      // We perform this synchronization using a barrier.
    }
    VLOG(1) << "RPC agent for " << workerInfo_.name_
            << " completed all client calls and is entering a barrier";
    processGroup_->barrier()->wait();
    {
      std::unique_lock<std::mutex> lock(callCountMutex_);
      // At this point, the count may have become non-zero again. We can't wait
      // for those calls to complete as other workers are waiting for us in the
      // allreduce and we would block them. Thus we send our count even if it is
      // non-zero and if anyone (be it us or another worker) has a non-zero
      // count we'll just do another round.
      VLOG(1) << "RPC agent for " << workerInfo_.name_
              << " exited the barrier and found " << clientActiveCalls_
              << " active client calls";
      std::vector<at::Tensor> totalClientActiveCalls = {
          at::zeros({}, at::kLong)};
      *totalClientActiveCalls[0].data_ptr<int64_t>() = clientActiveCalls_;
      processGroup_->allreduce(totalClientActiveCalls)->wait();
      VLOG(1) << "RPC agent for " << workerInfo_.name_
              << " completed the allreduce and got a total of "
              << (*totalClientActiveCalls[0].data_ptr<int64_t>())
              << " active client calls across all workers";
      if (*totalClientActiveCalls[0].data_ptr<int64_t>() == 0) {
        break;
      }
    }
  }
  VLOG(1) << "RPC agent for " << workerInfo_.name_ << " done joining";
}

void TensorPipeAgent::shutdownImpl() {
  // FIXME Isn't it too verbose for a library to print logs in normal operation?
  LOG(INFO) << "RPC agent for " << workerInfo_.name_ << " is shutting down";

  // Join the Timeout Thread
  timeoutThreadCV_.notify_one();
  if (timeoutThread_.joinable()) {
    timeoutThread_.join();
  }
  VLOG(1) << "RPC agent for " << workerInfo_.name_
          << " done waiting for timeout thread to join";

  // This will close all the pipes and listeners, invoke all callbacks with
  // errors, turn down the I/O event loops and wait for everything to terminate.
  context_->join();
  VLOG(1) << "RPC agent for " << workerInfo_.name_
          << " done waiting for TensorPipe context to join";

  // NOTE: We need to call waitWorkComplete in the end after we have shutdown
  // all listeners for Tensorpipe. This is to drain any already accepted work
  // in the ThreadPool. If this is done before we shutdown the listeners,
  // additional work could be added after this call and before we shutdown
  // listeners. This work would continue executing in the threadpool and might
  // cause issues during shutdown of the system.
  threadPool_.waitWorkComplete();
  VLOG(1) << "RPC agent for " << workerInfo_.name_
          << " done waiting for thread pool to complete work";
}

const WorkerInfo& TensorPipeAgent::getWorkerInfo(
    const std::string& workerName) const {
  const auto& it = workerNameToInfo_.find(workerName);
  TORCH_CHECK(
      it != workerNameToInfo_.end(), "Unknown destination worker ", workerName);
  return it->second;
}

const WorkerInfo& TensorPipeAgent::getWorkerInfo(worker_id_t workerId) const {
  const auto& it = workerIdToInfo_.find(workerId);
  TORCH_CHECK(
      it != workerIdToInfo_.end(), "Unknown destination worker ", workerId);
  return it->second;
}

std::vector<WorkerInfo> TensorPipeAgent::getWorkerInfos() const {
  std::vector<WorkerInfo> workerInfos;
  for (auto& item : workerNameToInfo_) {
    workerInfos.emplace_back(item.second);
  }
  return workerInfos;
}

const std::string& TensorPipeAgent::findWorkerURL(
    const WorkerInfo& worker) const {
  const auto it = workerNameToURL_.find(worker.name_);
  TORCH_CHECK(
      it != workerNameToURL_.end(), "Unknown worker name: ", worker.name_);
  return it->second;
}

#ifdef TP_ENABLE_SHM
std::string TensorPipeAgent::createUniqueShmAddr() {
  thread_local uint32_t threadLocalId = 0;
  return c10::str(
      "shm://tensorpipe_rpc_agent_",
      std::this_thread::get_id(),
      "_",
      ::getpid(),
      "_",
      threadLocalId++);
}
#endif

std::unordered_map<std::string, std::string> TensorPipeAgent::getMetrics() {
  std::unordered_map<std::string, std::string> metrics;
  metrics[kThreadPoolSize] = c10::to_string(threadPool_.size());
  metrics[kNumIdleThreads] = c10::to_string(threadPool_.numAvailable());
  {
    std::unique_lock<std::mutex> lock(callCountMutex_);
    metrics[kClientActiveCalls] = c10::to_string(clientActiveCalls_);
    metrics[kServerActiveCalls] = c10::to_string(serverActiveCalls_);
    metrics[kServerActiveAsyncCalls] = c10::to_string(serverActiveAsyncCalls_);
  }
  if (isGILProfilingEnabled()) {
    {
      std::unique_lock<std::mutex> lock(metricsMutex_);
      // Include the averages for each time series metric. This is just the GIL
      // Wait Time for now.
      auto averageGilWaitTime =
          timeSeriesMetrics_[kGilAverageWaitTime].computeAverage();
      lock.unlock();
      metrics[kGilAverageWaitTime] = c10::to_string(averageGilWaitTime);
    }
  }

  return metrics;
}

void TensorPipeAgent::addGilWaitTime(
    const std::chrono::microseconds gilWaitTime) {
  std::lock_guard<std::mutex> lock(metricsMutex_);
  timeSeriesMetrics_[kGilAverageWaitTime].addData(gilWaitTime.count());
}

TensorPipeAgent::NetworkDataDict TensorPipeAgent::getNetworkData() {
  std::lock_guard<std::mutex> lock(networkDataMutex_);
  return networkData_;
}

NetworkSourceInfo TensorPipeAgent::getNetworkSourceInfo() {
  NetworkSourceInfo info = {
      RpcAgent::getWorkerInfo().id_,
      nameToAddressStore_.get(RpcAgent::getWorkerInfo().name_)};

  return info;
}

void TensorPipeAgent::trackNetworkData(
    uint64_t requestSize,
    uint64_t responseSize,
    const std::string& destWorkerName) {
  std::lock_guard<std::mutex> lock(networkDataMutex_);
  networkData_[destWorkerName].numCalls++;
  networkData_[destWorkerName].totalSentBytes += requestSize;
  networkData_[destWorkerName].totalRecvBytes += responseSize;
}

void TensorPipeAgent::trackNetworkError(
    uint64_t requestSize,
    const std::string& destWorkerName) {
  std::lock_guard<std::mutex> lock(networkDataMutex_);
  networkData_[destWorkerName].numCalls++;
  networkData_[destWorkerName].totalSentBytes += requestSize;
  networkData_[destWorkerName].totalErrors++;
}

void TensorPipeAgent::increaseCallCount(int32_t& count) {
  {
    std::unique_lock<std::mutex> lock(callCountMutex_);
    ++count;
  }
  callCountCV_.notify_all();
}

void TensorPipeAgent::decreaseCallCount(int32_t& count) {
  {
    std::unique_lock<std::mutex> lock(callCountMutex_);
    --count;
  }
  callCountCV_.notify_all();
}

void TensorPipeAgent::markFutureAsComplete(
    std::shared_ptr<AtomicFutureMessage> futureMessage,
    Message message) {
  if (!futureMessage->isComplete.test_and_set()) {
    // Completing the future will run its callbacks, which could execute
    // arbitrary user code. To prevent blocking or stalling the TensorPipe event
    // loops, we defer this to a worker thread.
    threadPool_.run([this,
                     futureMessage{std::move(futureMessage)},
                     message{std::move(message)}]() mutable {
      futureMessage->futMsg.markCompleted(std::move(message));
      // The future's callbacks may schedule further RPCs, increasing the count.
      // Thus we must decrease it after completing the future, otherwise it may
      // briefly dip to zero and trick join into thinking all work is done.
      decreaseCallCount(clientActiveCalls_);
    });
  }
}

void TensorPipeAgent::markFutureWithError(
    std::shared_ptr<AtomicFutureMessage> futureMessage,
    std::string errorMsg) {
  if (!futureMessage->isComplete.test_and_set()) {
    // Completing the future will run its callbacks, which could execute
    // arbitrary user code. To prevent blocking or stalling the TensorPipe event
    // loops, we defer this to a worker thread.
    threadPool_.run([this,
                     futureMessage{std::move(futureMessage)},
                     errorMsg{std::move(errorMsg)}]() mutable {
      futureMessage->futMsg.setError(std::move(errorMsg));
      // The future's callbacks may schedule further RPCs, increasing the count.
      // Thus we must decrease it after completing the future, otherwise it may
      // briefly dip to zero and trick join into thinking all work is done.
      decreaseCallCount(clientActiveCalls_);
    });
  }
}

} // namespace rpc
} // namespace distributed
} // namespace torch
