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/*****************************************************************************
Copyright (c) 2012, 2015, Oracle and/or its affiliates. All Rights Reserved.
Copyright (c) 2017, 2019, MariaDB Corporation.
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 02110-1335 USA
*****************************************************************************/
/**************************************************//**
@file include/ut0counter.h
Counter utility class
Created 2012/04/12 by Sunny Bains
*******************************************************/
#ifndef ut0counter_h
#define ut0counter_h
#include "os0thread.h"
#include "my_rdtsc.h"
/** CPU cache line size */
#ifdef CPU_LEVEL1_DCACHE_LINESIZE
# define CACHE_LINE_SIZE CPU_LEVEL1_DCACHE_LINESIZE
#else
# error CPU_LEVEL1_DCACHE_LINESIZE is undefined
#endif /* CPU_LEVEL1_DCACHE_LINESIZE */
/** Use the result of my_timer_cycles(), which mainly uses RDTSC for cycles
as a random value. See the comments for my_timer_cycles() */
/** @return result from RDTSC or similar functions. */
static inline size_t
get_rnd_value()
{
size_t c = static_cast<size_t>(my_timer_cycles());
if (c != 0) {
return c;
}
/* We may go here if my_timer_cycles() returns 0,
so we have to have the plan B for the counter. */
#if !defined(_WIN32)
return (size_t)os_thread_get_curr_id();
#else
LARGE_INTEGER cnt;
QueryPerformanceCounter(&cnt);
return static_cast<size_t>(cnt.QuadPart);
#endif /* !_WIN32 */
}
/** Class for using fuzzy counters. The counter is multi-instance relaxed atomic
so 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 = 128 >
struct ib_counter_t {
/** Increment the counter by 1. */
void inc() { add(1); }
ib_counter_t& operator++() { inc(); return *this; }
/** Increment the counter by 1.
@param[in] index a reasonably thread-unique identifier */
void inc(size_t index) { add(index, 1); }
/** Add to the counter.
@param[in] n amount to be added */
void add(Type n) { add(get_rnd_value(), n); }
/** Add to the counter.
@param[in] index a reasonably thread-unique identifier
@param[in] n amount to be added */
void add(size_t index, Type n) {
index = index % N;
ut_ad(index < UT_ARR_SIZE(m_counter));
m_counter[index].value.fetch_add(n);
}
/* @return total value - not 100% accurate, since it is relaxed atomic*/
operator Type() const {
Type total = 0;
for (const auto &counter : m_counter) {
total += counter.value;
}
return(total);
}
private:
/** Atomic which occupies whole CPU cache line.
Note: We rely on the default constructor of std::atomic and
do not explicitly initialize the contents. This works for us,
because ib_counter_t is only intended for usage with global
memory that is allocated from the .bss and thus guaranteed to
be zero-initialized by the run-time environment.
@see srv_stats */
struct ib_counter_element_t {
MY_ALIGNED(CACHE_LINE_SIZE) Atomic_relaxed<Type> value;
};
static_assert(sizeof(ib_counter_element_t) == CACHE_LINE_SIZE, "");
/** Array of counter elements */
MY_ALIGNED(CACHE_LINE_SIZE) ib_counter_element_t m_counter[N];
};
#endif /* ut0counter_h */
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