transactor.hxx

/* Transactor framework, a wrapper for safely retryable transactions.
 *
 * DO NOT INCLUDE THIS FILE DIRECTLY; include pqxx/transactor instead.
 *
 * Copyright (c) 2001-2018, 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_TRANSACTOR
#define PQXX_H_TRANSACTOR

#include "pqxx/compiler-public.hxx"
#include "pqxx/compiler-internal-pre.hxx"

#include "pqxx/connection_base.hxx"
#include "pqxx/transaction.hxx"


// Methods tested in eg. test module test01 are marked with "//[t01]".

namespace pqxx
{


template<typename TRANSACTION_CALLBACK>
inline auto perform(const TRANSACTION_CALLBACK &callback, int attempts=3)
  -> decltype(callback())
{
  if (attempts <= 0)
    throw std::invalid_argument(
        "Zero or negative number of attempts passed to pqxx::perform().");

  for (; attempts > 0; --attempts)
  {
    try
    {
      return callback();
    }
    catch (const in_doubt_error &)
    {
      // Not sure whether transaction went through or not.  The last thing in
      // the world that we should do now is try again!
      throw;
    }
    catch (const statement_completion_unknown &)
    {
      // Not sure whether our last statement succeeded.  Don't risk running it
      // again.
      throw;
    }
    catch (const broken_connection &)
    {
      // Connection failed.  Definitely worth retrying.
      if (attempts <= 1) throw;
      continue;
    }
    catch (const transaction_rollback &)
    {
      // Some error that may well be transient, such as serialization failure
      // or deadlock.  Worth retrying.
      if (attempts <= 1) throw;
      continue;
    }
  }
  throw pqxx::internal_error("No outcome reached on perform().");
}


template<typename TRANSACTION=transaction<read_committed>> class transactor
{
public:
  using argument_type = TRANSACTION;
  explicit transactor(const std::string &TName="transactor") :          //[t04]
    m_name(TName) { }


  void operator()(TRANSACTION &T);                                      //[t04]

  // Overridable member functions, called by connection_base::perform() if an
  // attempt to run transaction fails/succeeds, respectively, or if the
  // connection is lost at just the wrong moment, goes into an indeterminate
  // state.  Use these to patch up runtime state to match events, if needed, or
  // to report failure conditions.


  void on_abort(const char[]) noexcept {}                               //[t13]


  void on_commit() {}                                                   //[t07]


  void on_doubt() noexcept {}                                           //[t13]

  std::string name() const { return m_name; }                           //[t13]

private:
  std::string m_name;
};


template<typename TRANSACTOR>
inline void connection_base::perform(
        const TRANSACTOR &T,
        int Attempts)
{
  if (Attempts <= 0) return;

  bool Done = false;

  // Make attempts to perform T
  do
  {
    --Attempts;

    // Work on a copy of T2 so we can restore the starting situation if need be
    TRANSACTOR T2(T);
    try
    {
      typename TRANSACTOR::argument_type X(*this, T2.name());
      T2(X);
      X.commit();
      Done = true;
    }
    catch (const in_doubt_error &)
    {
      // Not sure whether transaction went through or not.  The last thing in
      // the world that we should do now is retry.
      T2.on_doubt();
      throw;
    }
    catch (const std::exception &e)
    {
      // Could be any kind of error.
      T2.on_abort(e.what());
      if (Attempts <= 0) throw;
      continue;
    }
    catch (...)
    {
      // Don't try to forge ahead if we don't even know what happened
      T2.on_abort("Unknown exception");
      throw;
    }

    T2.on_commit();
  } while (!Done);
}
} // namespace pqxx
#include "pqxx/compiler-internal-post.hxx"
#endif