/* Copyright (c) 2012, 2014, Oracle and/or its affiliates. All rights reserved.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

   This program is also distributed with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have included with MySQL.

   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, version 2.0, 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
*/

#ifndef MT_LOCK_HPP
#define MT_LOCK_HPP

#include <ndb_global.h>
#include "mt-asm.h"
#include <NdbMutex.h>

#define JAM_FILE_ID 323


struct mt_lock_stat
{
  const void * m_ptr;
  char * m_name;
  Uint32 m_contended_count;
  Uint32 m_spin_count;
};

static void register_lock(const void * ptr, const char * name);

/**
 * We will disable use of spinlocks since it doesn't work properly
 * with realtime settings. Will also provide more stable results in
 * some environments at the expense of a minor optimisation. If
 * desirable to have optimal performance without usage of realtime
 * and always ensuring that each thread runs in its own processor,
 * then enable spinlocks again by removing comment on
 * #ifdef NDB_HAVE_XCNG
 */
#if defined(NDB_HAVE_XCNG) && defined(NDB_USE_SPINLOCK)
static mt_lock_stat * lookup_lock(const void * ptr);
struct thr_spin_lock
{
  thr_spin_lock(const char * name = 0)
  {
    m_lock = 0;
    register_lock(this, name);
  }

  volatile Uint32 m_lock;
};

static
ATTRIBUTE_NOINLINE
void
lock_slow(void * sl, volatile unsigned * val)
{
  mt_lock_stat* s = lookup_lock(sl); // lookup before owning lock

loop:
  Uint32 spins = 0;
  do {
    spins++;
    cpu_pause();
  } while (* val == 1);

  if (unlikely(xcng(val, 1) != 0))
    goto loop;

  if (s)
  {
    s->m_spin_count += spins;
    Uint32 count = ++s->m_contended_count;
    Uint32 freq = (count > 10000 ? 5000 : (count > 20 ? 200 : 1));

    if ((count % freq) == 0)
      printf("%s waiting for lock, contentions: %u spins: %u\n",
             s->m_name, count, s->m_spin_count);
  }
}

static
inline
void
lock(struct thr_spin_lock* sl)
{
  volatile unsigned* val = &sl->m_lock;
  if (likely(xcng(val, 1) == 0))
    return;

  lock_slow(sl, val);
}

static
inline
void
unlock(struct thr_spin_lock* sl)
{
  /**
   * Memory barrier here, to make sure all of our stores are visible before
   * the lock release is.
   *
   * NOTE: Bug#13870457 UNNECESSARY STRONG MEMORY BARRIER ...
   *       Suggest that a 'wmb' may have been sufficient here.
   *       However, as spinlocks are not used anymore, 
   *       (see fix for bug#16961971) this will not be fixed.
   */
  mb();
  sl->m_lock = 0;
}

static
inline
int
trylock(struct thr_spin_lock* sl)
{
  volatile unsigned* val = &sl->m_lock;
  return xcng(val, 1);
}
#else
#define thr_spin_lock thr_mutex
#endif

struct thr_mutex
{
  thr_mutex(const char * name = 0) {
    NdbMutex_Init(&m_mutex);
    register_lock(this, name);
  }

  NdbMutex m_mutex;
};

static
inline
void
lock(struct thr_mutex* sl)
{
  NdbMutex_Lock(&sl->m_mutex);
}

static
inline
void
unlock(struct thr_mutex* sl)
{
  NdbMutex_Unlock(&sl->m_mutex);
}

static
inline
int
trylock(struct thr_mutex* sl)
{
  return NdbMutex_Trylock(&sl->m_mutex);
}


#undef JAM_FILE_ID

#endif
