mirror of https://gitee.com/bigwinds/arangodb
110 lines
2.7 KiB
C++
110 lines
2.7 KiB
C++
////////////////////////////////////////////////////////////////////////////////
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/// DISCLAIMER
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///
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/// Copyright 2014-2017 ArangoDB GmbH, Cologne, Germany
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/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
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///
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/// Licensed under the Apache License, Version 2.0 (the "License");
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/// you may not use this file except in compliance with the License.
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/// You may obtain a copy of the License at
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///
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/// http://www.apache.org/licenses/LICENSE-2.0
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///
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/// Unless required by applicable law or agreed to in writing, software
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/// distributed under the License is distributed on an "AS IS" BASIS,
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/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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/// See the License for the specific language governing permissions and
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/// limitations under the License.
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///
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/// Copyright holder is ArangoDB GmbH, Cologne, Germany
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///
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/// @author Daniel H. Larkin
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////////////////////////////////////////////////////////////////////////////////
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#include "Cache/TransactionManager.h"
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#include "Basics/cpu-relax.h"
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#include "Cache/Transaction.h"
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#include <stdint.h>
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#include <atomic>
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using namespace arangodb::cache;
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TransactionManager::TransactionManager()
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: _openReads(0), _openSensitive(0), _openWrites(0), _term(0), _lock(false) {}
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Transaction* TransactionManager::begin(bool readOnly) {
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Transaction* tx = new Transaction(readOnly);
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lock();
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if (readOnly) {
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_openReads++;
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if (_openWrites.load() > 0) {
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tx->sensitive = true;
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_openSensitive++;
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}
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} else {
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tx->sensitive = true;
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if (_openSensitive.load() == 0) {
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_term++;
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}
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if (_openWrites.load() == 0) {
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_openSensitive = _openReads.load() + _openWrites.load();
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}
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_openWrites++;
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_openSensitive++;
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}
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tx->term = _term.load();
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unlock();
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return tx;
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}
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void TransactionManager::end(Transaction* tx) noexcept {
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TRI_ASSERT(tx != nullptr);
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lock();
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// if currently in sensitive phase, and transaction term is old, it was
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// upgraded to sensitive status
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if (((_term & static_cast<uint64_t>(1)) > 0) && (_term > tx->term)) {
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tx->sensitive = true;
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}
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if (tx->readOnly) {
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_openReads--;
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} else {
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_openWrites--;
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}
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if (tx->sensitive && (--_openSensitive == 0)) {
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_term++;
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}
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unlock();
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delete tx;
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}
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uint64_t TransactionManager::term() { return _term.load(); }
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void TransactionManager::lock() {
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while (true) {
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while (_lock.load(std::memory_order_relaxed)) {
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basics::cpu_relax();
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}
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bool expected = false;
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if (_lock.compare_exchange_weak(expected, true, std::memory_order_acq_rel,
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std::memory_order_relaxed)) {
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return;
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}
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basics::cpu_relax();
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}
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}
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void TransactionManager::unlock() {
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_lock.store(false, std::memory_order_release);
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}
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