mariadb-columnstore-engine/dbcon/joblist/threadsafequeue.h

/* Copyright (C) 2014 InfiniDB, Inc.

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License
   as published by the Free Software Foundation; version 2 of
   the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
   MA 02110-1301, USA. */

/*
 * $Id: threadsafequeue.h 9655 2013-06-25 23:08:13Z xlou $
 */

/** @file */
#pragma once

#include <atomic>
#include <unistd.h>
#include <queue>
#include <stdexcept>
#include <boost/thread.hpp>
#include <boost/shared_ptr.hpp>

namespace joblist
{
struct TSQSize_t
{
  size_t size;
  uint32_t count;
};

/** @brief A thread-safe queue class
 *
 * Implements most of the std::queue interface. All methods are protected via mutexes. The front() method
 * will block until something is in the queue. The push() method will signal all threads wating in front().
 * @warning This implementation is, despite its generic appearance, intended for JobList <-> PrimProc
 * communication. That is, it is designed to support multiple writers and @em one reader. If multiple readers
 * are needed, external synchronization around front() and pop() will be required.
 */
template <typename T>
class ThreadSafeQueue
{
 public:
  typedef T value_type;

  /** @brief constructor
   *
   * @warning this class takes ownership of the passed-in pointers.
   */
  ThreadSafeQueue(boost::mutex* pimplLock = nullptr, boost::condition* pimplCond = nullptr)
   : fShutdown(false), bytes(0), zeroCount(0)
  {
    fPimplLock.reset(pimplLock);
    fPimplCond.reset(pimplCond);
  }
  /** @brief destructor
   *
   */
  ~ThreadSafeQueue()
  {
#if 0

        try
        {
            shutdown();
        }
        catch (...)
        {
        }

#endif
  }
#if 0
    /** @brief get the head of the queue
     *
     * Return a read-only (constant) reference to the head of the queue, leaving it there. This method will block
     * until there is something to return.
     */
    const T& front() const
    {
        if (fPimplLock == 0 || fPimplCond == 0)
            throw std::runtime_error("TSQ: front() const: no sync!");

        boost::mutex::scoped_lock lk(*fPimplLock);

        if (fImpl.empty())
        {
            do
            {
                fPimplCond->wait(lk);

                if (fShutdown) return T();
            }
            while (fImpl.empty());
        }

        return fImpl.front();
    }
#endif
  /** @brief get the head of the queue
   *
   * Return a read/write reference to the head of the queue, leaving it there. This method will block
   * until there is something to return.
   */
  T& front()
  {
    if (fPimplLock == nullptr || fPimplCond == nullptr)
      throw std::runtime_error("TSQ: front(): no sync!");

    boost::mutex::scoped_lock lk(*fPimplLock);

    if (fImpl.empty())
    {
      do
      {
        fPimplCond->wait(lk);

        if (fShutdown)
          return fBs0;
      } while (fImpl.empty());
    }

    return fImpl.front();
  }

  /** @brief put an item on the end of the queue
   *
   * Signals all threads waiting in front() to continue.
   */
  TSQSize_t push(const T& v)
  {
    TSQSize_t ret = {0, 0};

    if (fPimplLock == nullptr || fPimplCond == nullptr)
      throw std::runtime_error("TSQ: push(): no sync!");

    if (fShutdown)
      return ret;

    boost::mutex::scoped_lock lk(*fPimplLock);
    fImpl.push(v);
    bytes += v->lengthWithHdrOverhead();
    fPimplCond->notify_one();
    ret.size = bytes;
    ret.count = static_cast<uint32_t>(fImpl.size());
    return ret;
  }
  /** @brief remove the front item in the queue
   *
   */
  TSQSize_t pop(T* out = NULL)
  {
    TSQSize_t ret = {0, 0};

    if (fPimplLock == nullptr)
      throw std::runtime_error("TSQ: pop(): no sync!");

    if (fShutdown)
    {
      *out = fBs0;
      return ret;
    }

    boost::mutex::scoped_lock lk(*fPimplLock);

    if (out != NULL)
    {
      if (fImpl.empty())
      {
        do
        {
          if (fShutdown)
          {
            *out = fBs0;
            return ret;
          }

          fPimplCond->wait(lk);

          if (fShutdown)
          {
            *out = fBs0;
            return ret;
          }
        } while (fImpl.empty());
      }

      *out = fImpl.front();
      bytes -= (*out)->lengthWithHdrOverhead();
    }

    fImpl.pop();
    ret.size = bytes;
    ret.count = static_cast<uint32_t>(fImpl.size());
    return ret;
  }

  /* If there are less than min elements in the queue, this fcn will return nothing
   * for up to 10 consecutive calls (poor man's timer).  On the 11th, it will return
   * the entire queue.  Note, the zeroCount var is non-critical.  Not a big deal if
   * it gets fudged now and then. */
  TSQSize_t pop_some(uint32_t divisor, std::vector<T>& t, uint32_t min = 1)
  {
    uint32_t curSize, workSize;
    TSQSize_t ret = {0, 0};

    if (fPimplLock == nullptr)
      throw std::runtime_error("TSQ: pop_some(): no sync!");

    t.clear();

    if (fShutdown)
      return ret;

    boost::mutex::scoped_lock lk(*fPimplLock);
    curSize = fImpl.size();

    if (curSize < min)
    {
      workSize = 0;
      zeroCount++;
    }
    else if (curSize / divisor <= min)
    {
      workSize = min;
      zeroCount = 0;
    }
    else
    {
      workSize = curSize / divisor;
      zeroCount = 0;
    }

    if (zeroCount > 10)
    {
      workSize = curSize;
      zeroCount = 0;
    }

    for (uint32_t i = 0; i < workSize; ++i)
    {
      t.push_back(fImpl.front());
      bytes -= fImpl.front()->lengthWithHdrOverhead();
      fImpl.pop();
    }

    ret.count = fImpl.size();
    ret.size = bytes;
    return ret;
  }

  inline void pop_all(std::vector<T>& t)
  {
    pop_some(1, t);
  }

  /** @brief is the queue empty
   *
   */
  bool empty() const
  {
    if (fPimplLock == nullptr)
      throw std::runtime_error("TSQ: empty(): no sync!");

    boost::mutex::scoped_lock lk(*fPimplLock);
    return fImpl.empty();
  }
  /** @brief how many items are in the queue
   *
   */
  TSQSize_t size() const
  {
    TSQSize_t ret;

    if (fPimplLock == nullptr)
      throw std::runtime_error("TSQ: size(): no sync!");

    boost::mutex::scoped_lock lk(*fPimplLock);
    ret.size = bytes;
    ret.count = fImpl.size();
    return ret;
  }

  /** @brief shutdown the queue
   *
   * cause all readers blocked in front() to return a default-constructed T
   */
  void shutdown()
  {
    fShutdown = true;

    if (fPimplCond != nullptr)
      fPimplCond->notify_all();
  }

  void clear()
  {
    if (fPimplLock == nullptr)
      throw std::runtime_error("TSQ: clear(): no sync!");

    boost::mutex::scoped_lock lk(*fPimplLock);

    while (!fImpl.empty())
      fImpl.pop();

    bytes = 0;
  }

 private:
  typedef std::queue<T> impl_type;
  typedef boost::shared_ptr<boost::mutex> SPBM;
  typedef boost::shared_ptr<boost::condition> SPBC;

  // defaults okay
  // ThreadSafeQueue<T>(const ThreadSafeQueue<T>& rhs);
  // ThreadSafeQueue<T>& operator=(const ThreadSafeQueue<T>& rhs);

  impl_type fImpl;
  SPBM fPimplLock;
  SPBC fPimplCond;
  std::atomic<bool> fShutdown;
  T fBs0;
  size_t bytes;
  uint32_t zeroCount;  // counts the # of times read_some returned 0
};

}  // namespace joblist