critical_section_tracker.cpp

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/*
 * Copyright 2008 Search Solution Corporation
 * Copyright 2016 CUBRID Corporation
 *
 *  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.
 *
 */

/*
 * critical_section_tracker.cpp - implementation for tracking and debugging critical sections usage
 */

#include "critical_section_tracker.hpp"

#include "resource_tracker.hpp"

#include <iostream>

namespace cubsync
{
  //

  static void
  cstrack_assert (bool cond)
  {
    cubbase::restrack_assert (cond);
  }

  critical_section_tracker::cstrack_entry::cstrack_entry (void)
    : m_enter_count (0)
    , m_is_writer (false)
    , m_is_demoted (false)
  {
    //
  }

  critical_section_tracker::critical_section_tracker (bool enable /* = false */)
    : m_cstrack_array {}
    , m_enabled (enable)
    , m_start_count (0)
  {
    //
  }

  void
  critical_section_tracker::on_enter_as_reader (int cs_index)
  {
    if (!m_enabled || !is_started ())
      {
    return;
      }

    check_csect_interdependencies (cs_index);

    cstrack_entry &cs_entry = m_cstrack_array[cs_index];

    // is first enter?
    if (cs_entry.m_enter_count == 0)
      {
    cstrack_assert (!cs_entry.m_is_writer && !cs_entry.m_is_demoted);
    cs_entry.m_enter_count++;
    return;
      }
    // is not first enter.
    assert (cs_entry.m_enter_count < MAX_REENTERS);

    if (cs_entry.m_is_writer)
      {
    // already entered as writer
    // this case is allowed. if I am a writer, I will not be blocked as readers
    cs_entry.m_enter_count++;
      }
    else if (cs_entry.m_is_demoted)
      {
    // I am not entirely sure why we allow when lock is demoted.
    cs_entry.m_enter_count++;
      }
    else
      {
    // re-enter is not accepted, since it may cause deadlocks.
    cs_entry.m_enter_count++;
    cstrack_assert (false);
      }
  }

  void
  critical_section_tracker::on_enter_as_writer (int cs_index)
  {
    if (!m_enabled || !is_started ())
      {
    return;
      }

    cstrack_entry &cs_entry = m_cstrack_array[cs_index];

    check_csect_interdependencies (cs_index);

    // is first enter?
    if (cs_entry.m_enter_count == 0)
      {
    cstrack_assert (!cs_entry.m_is_writer && !cs_entry.m_is_demoted);
    cs_entry.m_is_writer = true;
    cs_entry.m_enter_count++;
    return;
      }
    // is not first enter.

    // re-enter is only accepted if it was already writer
    cstrack_assert (cs_entry.m_is_writer);
    cs_entry.m_enter_count++;
  }

  void
  critical_section_tracker::on_promote (int cs_index)
  {
    if (!m_enabled || !is_started ())
      {
    return;
      }

    cstrack_entry &cs_entry = m_cstrack_array[cs_index];

    // I must be reader
    cstrack_assert (!cs_entry.m_is_writer);
    cstrack_assert (cs_entry.m_enter_count == 1);

    cs_entry.m_is_writer = true;
    cs_entry.m_is_demoted = false;
  }

  void
  critical_section_tracker::on_demote (int cs_index)
  {
    if (!m_enabled || !is_started ())
      {
    return;
      }

    cstrack_entry &cs_entry = m_cstrack_array[cs_index];

    // I must be writer
    cstrack_assert (cs_entry.m_is_writer);
    cstrack_assert (cs_entry.m_enter_count == 1);

    cs_entry.m_is_writer = false;
    cs_entry.m_is_demoted = true;
  }

  void
  critical_section_tracker::on_exit (int cs_index)
  {
    if (!m_enabled || !is_started ())
      {
    return;
      }

    cstrack_entry &cs_entry = m_cstrack_array[cs_index];

    if (cs_entry.m_enter_count == 0)
      {
    cstrack_assert (false);
    return;
      }

    --cs_entry.m_enter_count;
    if (cs_entry.m_enter_count == 0)
      {
    cs_entry.m_is_demoted = false;
    cs_entry.m_is_writer = false;
      }
  }

  void
  critical_section_tracker::check_csect_interdependencies (int cs_index)
  {
    if (cs_index == CSECT_LOCATOR_SR_CLASSNAME_TABLE)
      {
    cstrack_assert (m_cstrack_array[CSECT_CT_OID_TABLE].m_enter_count == 0);
      }
  }

  bool
  critical_section_tracker::is_started (void)
  {
    return m_start_count > 0;
  }

  void
  critical_section_tracker::start (void)
  {
    if (!m_enabled)
      {
    return;
      }
    m_start_count++;
  }

  void
  critical_section_tracker::stop (void)
  {
    if (!m_enabled)
      {
    return;
      }

    if (m_start_count == 0)
      {
    cstrack_assert (false);
      }
    else
      {
    m_start_count--;
      }

    if (m_start_count == 0)
      {
    // check no critical section is entered
    clear_all ();
      }
  }

  void
  critical_section_tracker::check (void)
  {
    bool m_printed_header = false;
    std::ostream &os = std::cerr;

    for (int cs_index = 0; cs_index < CRITICAL_SECTION_COUNT; cs_index++)
      {
    if (m_cstrack_array[cs_index].m_enter_count > 0)
      {
        if (!m_printed_header)
          {
        os << "   +--- Critical Sections" << std::endl;
        m_printed_header = true;
          }
        os << "     +--- " << csect_name_at (cs_index) << std::endl;
        os << "       +--- enter count = " << m_cstrack_array[cs_index].m_enter_count << std::endl;
        os << "       +--- is writer = " << m_cstrack_array[cs_index].m_is_writer << std::endl;
        os << "       +--- is demoted = " << m_cstrack_array[cs_index].m_is_demoted << std::endl;

        cstrack_assert (false);
      }
      }
  }

  void
  critical_section_tracker::clear_all (void)
  {
    check ();
    for (int cs_index = 0; cs_index < CRITICAL_SECTION_COUNT; cs_index++)
      {
    // reset
    m_cstrack_array[cs_index] = {};
      }
    m_start_count = 0;
  }
} // namespace cubsync