159 lines
4.7 KiB
C++
159 lines
4.7 KiB
C++
/*****************************************************************************
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Copyright (c) 2017, 2018, Oracle and/or its affiliates. All Rights Reserved.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License, version 2.0,
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as published by the Free Software Foundation.
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This program is also distributed with certain software (including
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but not limited to OpenSSL) that is licensed under separate terms,
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as designated in a particular file or component or in included license
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documentation. The authors of MySQL hereby grant you an additional
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permission to link the program and your derivative works with the
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separately licensed software that they have included with MySQL.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License, version 2.0, for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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Portions of this file contain modifications contributed and copyrighted by
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Google, Inc. Those modifications are gratefully acknowledged and are described
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briefly in the InnoDB documentation. The contributions by Google are
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incorporated with their permission, and subject to the conditions contained in
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the file COPYING.Google.
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*****************************************************************************/
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/**************************************************/ /**
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@file include/sync0sharded_rw.h
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The sharded read-write lock (for threads).
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The s-lock scales better than in single rw-lock,
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but the x-lock is much slower.
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*******************************************************/
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#ifndef sync0sharded_rw_h
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#define sync0sharded_rw_h
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#include "sync0rw.h"
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#include "ut0rnd.h"
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#include "ut0ut.h"
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#ifndef UNIV_HOTBACKUP
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#ifndef UNIV_LIBRARY
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/** Rw-lock with very fast, highly concurrent s-lock but slower x-lock.
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It's basically array of rw-locks. When s-lock is being acquired, single
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rw-lock from array is selected randomly and s-locked. Therefore, all
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rw-locks from array has to be x-locked when x-lock is being acquired.
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Purpose of this data structure is to reduce contention on single atomic
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in single rw-lock when a lot of threads need to acquire s-lock very often,
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but x-lock is very rare. */
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class Sharded_rw_lock {
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public:
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void create(mysql_pfs_key_t pfs_key, latch_level_t latch_level,
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size_t n_shards) {
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m_n_shards = n_shards;
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m_shards = static_cast<Shard *>(ut_zalloc_nokey(sizeof(Shard) * n_shards));
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for_each([pfs_key, latch_level](rw_lock_t &lock) {
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static_cast<void>(latch_level); // clang -Wunused-lambda-capture
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rw_lock_create(pfs_key, &lock, latch_level);
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});
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}
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void free() {
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ut_a(m_shards != nullptr);
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for_each([](rw_lock_t &lock) { rw_lock_free(&lock); });
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ut_free(m_shards);
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m_shards = nullptr;
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m_n_shards = 0;
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}
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size_t s_lock() {
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const size_t shard_no = ut_rnd_interval(0, m_n_shards - 1);
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rw_lock_s_lock(&m_shards[shard_no].lock);
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return shard_no;
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}
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ibool s_lock_nowait(size_t &shard_no, const char *file, ulint line) {
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shard_no = ut_rnd_interval(0, m_n_shards - 1);
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return rw_lock_s_lock_nowait(&m_shards[shard_no].lock, file, line);
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}
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void s_unlock(size_t shard_no) {
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ut_a(shard_no < m_n_shards);
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rw_lock_s_unlock(&m_shards[shard_no].lock);
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}
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void x_lock() {
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for_each([](rw_lock_t &lock) { rw_lock_x_lock(&lock); });
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}
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void x_unlock() {
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for_each([](rw_lock_t &lock) { rw_lock_x_unlock(&lock); });
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}
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#ifdef UNIV_DEBUG
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bool s_own(size_t shard_no) const {
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return rw_lock_own(&m_shards[shard_no].lock, RW_LOCK_S);
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}
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bool x_own() const { return rw_lock_own(&m_shards[0].lock, RW_LOCK_X); }
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#endif /* !UNIV_DEBUG */
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private:
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struct Shard {
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rw_lock_t lock;
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char pad[INNOBASE_CACHE_LINE_SIZE];
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};
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template <typename F>
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void for_each(F f) {
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std::for_each(m_shards, m_shards + m_n_shards,
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[&f](Shard &shard) { f(shard.lock); });
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}
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Shard *m_shards = nullptr;
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size_t m_n_shards = 0;
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};
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#else /* !UNIV_LIBRARY */
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/* For UNIV_LIBRARY, rw_lock is no-op, so sharded rw-lock is also no-op. */
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class Sharded_rw_lock {
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public:
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void create(mysql_pfs_key_t pfs_key, latch_level_t latch_level,
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size_t n_shards) {}
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void free() {}
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size_t s_lock() { return 0; }
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void s_unlock(size_t shard_no) { ut_a(shard_no == 0); }
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void x_lock() {}
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void x_unlock() {}
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};
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#endif /* UNIV_LIBRARY */
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#endif /* UNIV_HOTBACKUP */
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#endif /* sync0sharded_rw.h */
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