/*****************************************************************************

Copyright (c) 2012, 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 as published by the Free Software
Foundation; version 2 of the License.

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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

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this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA

*****************************************************************************/

/**************************************************/ /**
 @file include/ut0counter.h

 Counter utility class

 Created 2012/04/12 by Sunny Bains
 *******************************************************/

#ifndef UT0COUNTER_H
#define UT0COUNTER_H

#include "my_dbug.h"
#include <string.h>

#include <array>
#include <atomic>
#include <functional>

/** CPU cache line size */
#ifndef CACHE_LINE_SIZE
#define CACHE_LINE_SIZE 64
#endif

/** Default number of slots to use in ib_counter_t */
#define IB_N_SLOTS 64

#ifdef __WIN__
#define get_curr_thread_id() GetCurrentThreadId()
#else
#define get_curr_thread_id() pthread_self()
#endif

#define UT_ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))

/** Get the offset into the counter array. */
template <typename Type, int N> struct generic_indexer_t {
  /** Default constructor/destructor should be OK. */

  /** @return offset within m_counter */
  size_t offset(size_t index) const {
    return (((index % N) + 1) * (CACHE_LINE_SIZE / sizeof(Type)));
  }
};

#ifdef HAVE_SCHED_GETCPU
//#include <utmpx.h>  // Including this causes problems with EMPTY symbol
#include <sched.h>  // Include this instead
/** Use the cpu id to index into the counter array. If it fails then
use the thread id. */
template <typename Type, int N>
struct get_sched_indexer_t : public generic_indexer_t<Type, N> {
  /** Default constructor/destructor should be OK. */

  /* @return result from sched_getcpu(), the thread id if it fails. */
  size_t get_rnd_index() const {

    size_t cpu = sched_getcpu();
    if (cpu == (size_t)-1) {
      cpu = get_curr_thread_id();
    }

    return (cpu);
  }
};
#endif /* HAVE_SCHED_GETCPU */

/** Use the thread id to index into the counter array. */
template <typename Type, int N>
struct thread_id_indexer_t : public generic_indexer_t<Type, N> {
  /** Default constructor/destructor should are OK. */

  /* @return a random number, currently we use the thread id. Where
  thread id is represented as a pointer, it may not work as
  effectively. */
  size_t get_rnd_index() const { return get_curr_thread_id(); }
};

/** For counters wher N=1 */
template <typename Type, int N = 1> struct single_indexer_t {
  /** Default constructor/destructor should are OK. */

  /** @return offset within m_counter */
  size_t offset(size_t index) const {
    DBUG_ASSERT(N == 1);
    return ((CACHE_LINE_SIZE / sizeof(Type)));
  }

  /* @return 1 */
  size_t get_rnd_index() const {
    DBUG_ASSERT(N == 1);
    return (1);
  }
};

/** Class for using fuzzy counters. The counter is not protected by any
mutex and the results are not guaranteed to be 100% accurate but close
enough. Creates an array of counters and separates each element by the
CACHE_LINE_SIZE bytes */
template <typename Type, int N = IB_N_SLOTS,
          template <typename, int> class Indexer = thread_id_indexer_t>
class ib_counter_t {
 public:
  ib_counter_t() { memset(m_counter, 0x0, sizeof(m_counter)); }

  ~ib_counter_t() { DBUG_ASSERT(validate()); }

  bool validate() {
#ifdef UNIV_DEBUG
    size_t n = (CACHE_LINE_SIZE / sizeof(Type));

    /* Check that we aren't writing outside our defined bounds. */
    for (size_t i = 0; i < UT_ARRAY_SIZE(m_counter); i += n) {
      for (size_t j = 1; j < n - 1; ++j) {
        DBUG_ASSERT(m_counter[i + j] == 0);
      }
    }
#endif /* UNIV_DEBUG */
    return (true);
  }

  /** If you can't use a good index id. Increment by 1. */
  void inc() { add(1); }

  /** If you can't use a good index id.
   * @param n  - is the amount to increment */
  void add(Type n) {
    size_t i = m_policy.offset(m_policy.get_rnd_index());

    DBUG_ASSERT(i < UT_ARRAY_SIZE(m_counter));

    m_counter[i] += n;
  }

  /** Use this if you can use a unique indentifier, saves a
  call to get_rnd_index().
  @param i - index into a slot
  @param n - amount to increment */
  void add(size_t index, Type n) {
    size_t i = m_policy.offset(index);

    DBUG_ASSERT(i < UT_ARRAY_SIZE(m_counter));

    m_counter[i] += n;
  }

  /** If you can't use a good index id. Decrement by 1. */
  void dec() { sub(1); }

  /** If you can't use a good index id.
   * @param - n is the amount to decrement */
  void sub(Type n) {
    size_t i = m_policy.offset(m_policy.get_rnd_index());

    DBUG_ASSERT(i < UT_ARRAY_SIZE(m_counter));

    m_counter[i] -= n;
  }

  /** Use this if you can use a unique indentifier, saves a
  call to get_rnd_index().
  @param i - index into a slot
  @param n - amount to decrement */
  void sub(size_t index, Type n) {
    size_t i = m_policy.offset(index);

    DBUG_ASSERT(i < UT_ARRAY_SIZE(m_counter));

    m_counter[i] -= n;
  }

  /* @return total value - not 100% accurate, since it is not atomic. */
  operator Type() const {
    Type total = 0;

    for (size_t i = 0; i < N; ++i) {
      total += m_counter[m_policy.offset(i)];
    }

    return (total);
  }

 private:
  /** Indexer into the array */
  Indexer<Type, N> m_policy;

  /** Slot 0 is unused. */
  Type m_counter[(N + 1) * (CACHE_LINE_SIZE / sizeof(Type))];
};

/** Sharded atomic counter. */
namespace Counter {

using Type = uint64_t;

using N = std::atomic<Type>;

static_assert(CACHE_LINE_SIZE >= sizeof(N),
              "Atomic counter size > CACHE_LINE_SIZE");

using Pad = char[CACHE_LINE_SIZE - sizeof(N)];

/** Counter shard. */
struct Shard {
  /** Separate on cache line. */
  Pad m_pad;

  /** Sharded counter. */
  N m_n{};
};

using Shards = std::array<Shard, 128>;
using Function = std::function<void(const Type)>;

/** Increment the counter of a shard by 1.
@param[in,out]  shards          Sharded counter to increment.
@param[in] id                   Shard key. */
inline void inc(Shards &shards, size_t id) {
  shards[id % shards.size()].m_n.fetch_add(1, std::memory_order_relaxed);
}

/** Increment the counter for a shard by n.
@param[in,out]  shards          Sharded counter to increment.
@param[in] id                   Shard key.
@param[in] n                    Number to add. */
inline void add(Shards &shards, size_t id, size_t n) {
  shards[id % shards.size()].m_n.fetch_add(n, std::memory_order_relaxed);
}

/** Get the counter value for a shard.
@param[in,out]  shards          Sharded counter to increment.
@param[in] id                   Shard key. */
inline Type get(const Shards &shards, size_t id) {
  return (shards[id % shards.size()].m_n.load(std::memory_order_relaxed));
}

/** Iterate over the shards.
@param[in] shards               Shards to iterate over
@param[in] f                    Callback function
@return total value. */
inline void for_each(const Shards &shards, Function &&f) {
  for (const auto &shard : shards) {
    f(shard.m_n);
  }
}

/** Get the total value of all shards.
@param[in] shards               Shards to sum.
@return total value. */
inline Type total(const Shards &shards) {
  Type n = 0;

  for_each(shards, [&](const Type count) { n += count; });

  return (n);
}

/** Clear the counter - reset to 0.
@param[in,out] shards          Shards to clear. */
inline void clear(Shards &shards) {
  for (auto &shard : shards) {
    shard.m_n.store(0, std::memory_order_relaxed);
  }
}

}  // namespace Counter

#endif /* UT0COUNTER_H */