pipeline.hxx

/* Definition of the pqxx::pipeline class.
 *
 *   Throughput-optimized mechanism for executing queries.
 *
 * DO NOT INCLUDE THIS FILE DIRECTLY; include pqxx/pipeline instead.
 *
 * Copyright (c) 2000-2022, Jeroen T. Vermeulen.
 *
 * See COPYING for copyright license.  If you did not receive a file called
 * COPYING with this source code, please notify the distributor of this
 * mistake, or contact the author.
 */
#ifndef PQXX_H_PIPELINE
#define PQXX_H_PIPELINE

#if !defined(PQXX_HEADER_PRE)
#  error "Include libpqxx headers as <pqxx/header>, not <pqxx/header.hxx>."
#endif

#include <limits>
#include <map>
#include <string>

#include "pqxx/transaction_base.hxx"


namespace pqxx
{
// TODO: libpq 14 introduced a similar "pipeline mode."  Can we use that?


class PQXX_LIBEXPORT pipeline : public transaction_focus
{
public:
  using query_id = long;

  pipeline(pipeline const &) = delete;
  pipeline &operator=(pipeline const &) = delete;

  explicit pipeline(transaction_base &t) : transaction_focus{t, s_classname}
  {
    init();
  }
  pipeline(transaction_base &t, std::string_view tname) :
          transaction_focus{t, s_classname, tname}
  {
    init();
  }

  ~pipeline() noexcept;


  query_id insert(std::string_view) &;


  void complete();


  void flush();


  void cancel();

  [[nodiscard]] bool is_finished(query_id) const;


  result retrieve(query_id qid)
  {
    return retrieve(m_queries.find(qid)).second;
  }


  std::pair<query_id, result> retrieve();

  [[nodiscard]] bool empty() const noexcept { return std::empty(m_queries); }


  int retain(int retain_max = 2) &;


  void resume() &;

private:
  struct PQXX_PRIVATE Query
  {
    explicit Query(std::string_view q) :
            query{std::make_shared<std::string>(q)}
    {}

    std::shared_ptr<std::string> query;
    result res;
  };

  using QueryMap = std::map<query_id, Query>;

  void init();
  void attach();
  void detach();

  static constexpr query_id qid_limit() noexcept
  {
    // Parenthesise this to work around an eternal Visual C++ problem:
    // Without the extra parentheses, unless NOMINMAX is defined, the
    // preprocessor will mistake this "max" for its annoying built-in macro
    // of the same name.
    return (std::numeric_limits<query_id>::max)();
  }

  PQXX_PRIVATE query_id generate_id();

  bool have_pending() const noexcept
  {
    return m_issuedrange.second != m_issuedrange.first;
  }

  PQXX_PRIVATE void issue();

  void set_error_at(query_id qid) noexcept
  {
    PQXX_UNLIKELY
    if (qid < m_error)
      m_error = qid;
  }

  [[noreturn]] PQXX_PRIVATE void internal_error(std::string const &err);

  PQXX_PRIVATE bool obtain_result(bool expect_none = false);

  PQXX_PRIVATE void obtain_dummy();
  PQXX_PRIVATE void get_further_available_results();
  PQXX_PRIVATE void check_end_results();

  PQXX_PRIVATE void receive_if_available();

  PQXX_PRIVATE void receive(pipeline::QueryMap::const_iterator stop);
  std::pair<pipeline::query_id, result> retrieve(pipeline::QueryMap::iterator);

  QueryMap m_queries;
  std::pair<QueryMap::iterator, QueryMap::iterator> m_issuedrange;
  int m_retain = 0;
  int m_num_waiting = 0;
  query_id m_q_id = 0;

  bool m_dummy_pending = false;

  query_id m_error = qid_limit();


  internal::encoding_group m_encoding;

  static constexpr std::string_view s_classname{"pipeline"};
};
} // namespace pqxx
#endif