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101 lines
3.3 KiB
C++
101 lines
3.3 KiB
C++
/*****************************************************************************
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Copyright (c) 2012, 2015, Oracle and/or its affiliates. All Rights Reserved.
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Copyright (c) 2017, 2019, MariaDB Corporation.
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This program is free software; you can redistribute it and/or modify it under
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the terms of the GNU General Public License as published by the Free Software
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Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
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You should have received a copy of the GNU General Public License along with
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this program; if not, write to the Free Software Foundation, Inc.,
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51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA
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*****************************************************************************/
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/**************************************************//**
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@file include/ut0counter.h
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Counter utility class
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Created 2012/04/12 by Sunny Bains
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*******************************************************/
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#ifndef ut0counter_h
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#define ut0counter_h
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#include "os0thread.h"
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#include "my_rdtsc.h"
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/** CPU cache line size */
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#ifdef CPU_LEVEL1_DCACHE_LINESIZE
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# define CACHE_LINE_SIZE CPU_LEVEL1_DCACHE_LINESIZE
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#else
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# error CPU_LEVEL1_DCACHE_LINESIZE is undefined
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#endif /* CPU_LEVEL1_DCACHE_LINESIZE */
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/** Default number of slots to use in ib_counter_t */
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#define IB_N_SLOTS 64
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/** Class for using fuzzy counters. The counter is multi-instance relaxed atomic
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so the results are not guaranteed to be 100% accurate but close
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enough. Creates an array of counters and separates each element by the
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CACHE_LINE_SIZE bytes */
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template <typename Type, int N = IB_N_SLOTS>
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struct ib_counter_t {
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/** Increment the counter by 1. */
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void inc() { add(1); }
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/** Increment the counter by 1.
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@param[in] index a reasonably thread-unique identifier */
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void inc(size_t index) { add(index, 1); }
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/** Add to the counter.
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@param[in] n amount to be added */
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void add(Type n) { add(size_t(my_pseudo_random()), n); }
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/** Add to the counter.
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@param[in] index a reasonably thread-unique identifier
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@param[in] n amount to be added */
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void add(size_t index, Type n) {
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index = index % N;
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ut_ad(index < UT_ARR_SIZE(m_counter));
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m_counter[index].value.fetch_add(n, std::memory_order_relaxed);
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}
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/* @return total value - not 100% accurate, since it is relaxed atomic*/
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operator Type() const {
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Type total = 0;
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for (const auto &counter : m_counter) {
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total += counter.value.load(std::memory_order_relaxed);
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}
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return(total);
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}
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private:
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/** Atomic which occupies whole CPU cache line.
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Note: We rely on the default constructor of std::atomic and
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do not explicitly initialize the contents. This works for us,
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because ib_counter_t is only intended for usage with global
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memory that is allocated from the .bss and thus guaranteed to
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be zero-initialized by the run-time environment.
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@see srv_stats
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@see rw_lock_stats */
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struct ib_counter_element_t {
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MY_ALIGNED(CACHE_LINE_SIZE) std::atomic<Type> value;
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};
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static_assert(sizeof(ib_counter_element_t) == CACHE_LINE_SIZE, "");
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/** Array of counter elements */
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MY_ALIGNED(CACHE_LINE_SIZE) ib_counter_element_t m_counter[N];
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};
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#endif /* ut0counter_h */
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