ZeroMQSvc.h

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/*
 * Project: RooFit
 * Authors:
 *   RA, Roel Aaij, NIKHEF
 *   PB, Patrick Bos, Netherlands eScience Center, p.bos@esciencecenter.nl
 *
 * Copyright (c) 2021, CERN
 *
 * Redistribution and use in source and binary forms,
 * with or without modification, are permitted according to the terms
 * listed in LICENSE (http://roofit.sourceforge.net/license.txt)
 */
 
#ifndef ZEROMQ_IZEROMQSVC_H
#define ZEROMQ_IZEROMQSVC_H 1
 
#include <zmq.hpp>
#include "RooFit_ZMQ/Utility.h"
#include "RooFit_ZMQ/functions.h"
 
#include <type_traits>
#include <string>
#include <vector>
#include <sstream>
#include <ios>
#include <iostream> // std::cerr
#include <functional>
#include <memory>
 
// debugging
#include <unistd.h> // getpid
 
namespace ZMQ {
 
struct TimeOutException : std::exception {
   TimeOutException() = default;
};
 
struct MoreException : std::exception {
   MoreException() = default;
};
 
} // namespace ZMQ
 
template <int PERIOD = 0>
struct ZmqLingeringSocketPtrDeleter {
   void operator()(zmq::socket_t *socket)
   {
      int tries = 0;
      int max_tries = 3;
      while (true) {
         try {
            // the actual work this function should do, plus the delete socket below:
            if (socket)
               socket->set(zmq::sockopt::linger, PERIOD);
            break;
         } catch (zmq::error_t &e) {
            if (++tries == max_tries || e.num() == EINVAL || e.num() == ETERM ||
                e.num() == ENOTSOCK // not recoverable from here
            ) {
               std::cerr << "ERROR in ZeroMQSvc::socket: " << e.what() << " (errno: " << e.num() << ")\n";
               throw;
            }
            std::cerr << "RETRY " << tries << "/" << (max_tries - 1)
                      << " in ZmqLingeringSocketPtrDeleter: call interrupted (errno: " << e.num() << ")\n";
         }
      }
 
      delete socket;
   }
};
 
template <int PERIOD = 0>
using ZmqLingeringSocketPtr = std::unique_ptr<zmq::socket_t, ZmqLingeringSocketPtrDeleter<PERIOD>>;
 
// We retry send and receive only on EINTR, all other errors are either fatal, or can only
// be handled at the caller.
template <typename... args_t>
auto retry_send(zmq::socket_t &socket, int max_tries, args_t... args) -> decltype(socket.send(args...))
{
   int tries = 0;
   while (true) {
      try {
         // the actual work this function should do, all the rest is error handling:
         return socket.send(args...);
      } catch (zmq::error_t &e) {
         if (++tries == max_tries || e.num() != EINTR // only recoverable error
         ) {
            throw;
         }
         std::cerr << "RETRY " << tries << "/" << (max_tries - 1) << " in ZeroMQSvc::send (retry_send) on pid "
                   << getpid() << ": " << e.what() << ")\n";
      }
   }
}
 
template <typename... args_t>
auto retry_recv(zmq::socket_t &socket, int max_tries, args_t... args) -> decltype(socket.recv(args...))
{
   int tries = 0;
   while (true) {
      try {
         // the actual work this function should do, all the rest is error handling:
         return socket.recv(args...);
      } catch (zmq::error_t &e) {
         if (++tries == max_tries || e.num() != EINTR // only recoverable error
         ) {
            throw;
         }
         std::cerr << "RETRY " << tries << "/" << (max_tries - 1) << " in ZeroMQSvc::recv (retry_recv) on pid "
                   << getpid() << ": " << e.what() << ")\n";
      }
   }
}
 
class ZeroMQSvc {
   // Note on error handling:
   // Creating message_t can throw, but only when memory ran out (errno ENOMEM),
   // and that is something only the caller can fix, so we don't catch it here.
 
public:
   enum Encoding { Text = 0, Binary };
 
   Encoding encoding() const;
   void setEncoding(const Encoding &e);
   zmq::context_t &context() const;
   zmq::socket_t socket(zmq::socket_type type) const;
   zmq::socket_t *socket_ptr(zmq::socket_type type) const;
   void close_context() const;
 
   /// decode message with ZMQ, POD version
   template <class T, typename std::enable_if<!std::is_pointer<T>::value && ZMQ::Detail::is_trivial<T>::value, T>::type
                         * = nullptr>
   T decode(const zmq::message_t &msg) const
   {
      T object;
      memcpy(&object, msg.data(), msg.size());
      return object;
   }
 
   /// decode ZMQ message, string version
   template <class T, typename std::enable_if<std::is_same<T, std::string>::value, T>::type * = nullptr>
   std::string decode(const zmq::message_t &msg) const
   {
      std::string r(msg.size() + 1, char{});
      r.assign(static_cast<const char *>(msg.data()), msg.size());
      return r;
   }
 
   /// receive message with ZMQ, general version
   // FIXME: what to do with flags=nullptr.... more is a pointer, that might prevent conversion
   template <class T, typename std::enable_if<!(std::is_same<zmq::message_t, T>::value), T>::type * = nullptr>
   T receive(zmq::socket_t &socket, zmq::recv_flags flags = zmq::recv_flags::none, bool *more = nullptr) const
   {
      // receive message
      zmq::message_t msg;
      auto recv_result = retry_recv(socket, 2, std::ref(msg), flags);
      if (!recv_result) {
         throw ZMQ::TimeOutException{};
      }
      if (more)
         *more = msg.more();
 
      // decode message
      return decode<T>(msg);
   }
 
   /// receive message with ZMQ
   template <class T, typename std::enable_if<std::is_same<zmq::message_t, T>::value, T>::type * = nullptr>
   T receive(zmq::socket_t &socket, zmq::recv_flags flags = zmq::recv_flags::none, bool *more = nullptr) const
   {
      // receive message
      zmq::message_t msg;
      auto recv_result = retry_recv(socket, 2, std::ref(msg), flags);
      if (!recv_result) {
         throw ZMQ::TimeOutException{};
      }
      if (more)
         *more = msg.more();
      return msg;
   }
 
   /// encode message to ZMQ
   template <class T, typename std::enable_if<!std::is_pointer<T>::value && ZMQ::Detail::is_trivial<T>::value, T>::type
                         * = nullptr>
   zmq::message_t encode(const T &item, std::function<size_t(const T &t)> sizeFun = ZMQ::defaultSizeOf<T>) const
   {
      size_t s = sizeFun(item);
      zmq::message_t msg{s};
      memcpy((void *)msg.data(), &item, s);
      return msg;
   }
 
   zmq::message_t encode(const char *item) const;
   zmq::message_t encode(const std::string &item) const;
 
   /// Send message with ZMQ
   template <class T, typename std::enable_if<!std::is_same<T, zmq::message_t>::value, T>::type * = nullptr>
   zmq::send_result_t send(zmq::socket_t &socket, const T &item, zmq::send_flags flags = zmq::send_flags::none) const
   {
      return retry_send(socket, 1, encode(item), flags);
   }
 
   zmq::send_result_t
   send(zmq::socket_t &socket, const char *item, zmq::send_flags flags = zmq::send_flags::none) const;
   zmq::send_result_t
   send(zmq::socket_t &socket, zmq::message_t &msg, zmq::send_flags flags = zmq::send_flags::none) const;
   zmq::send_result_t
   send(zmq::socket_t &socket, zmq::message_t &&msg, zmq::send_flags flags = zmq::send_flags::none) const;
 
private:
   Encoding m_enc = Text;
   mutable zmq::context_t *m_context = nullptr;
};
 
ZeroMQSvc &zmqSvc();
 
#endif // ZEROMQ_IZEROMQSVC_H