mirror of https://gitee.com/bigwinds/arangodb
101 lines
3.0 KiB
C++
101 lines
3.0 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/BucketState.h"
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#include "Basics/Common.h"
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#include "Basics/cpu-relax.h"
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#include "Basics/debugging.h"
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#include <stdint.h>
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#include <atomic>
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using namespace arangodb::basics;
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using namespace arangodb::cache;
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BucketState::BucketState() : _state(0) {}
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BucketState::BucketState(BucketState const& other)
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: _state(other._state.load()) {}
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BucketState& BucketState::operator=(BucketState const& other) {
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if (this != &other) {
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_state = other._state.load();
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}
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return *this;
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}
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bool BucketState::isLocked() const {
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return ((_state.load() & static_cast<uint32_t>(Flag::locked)) > 0);
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}
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bool BucketState::lock(uint64_t maxTries, BucketState::CallbackType cb) {
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uint64_t attempt = 0;
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while (attempt < maxTries) {
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// expect unlocked, but need to preserve migrating status
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uint32_t current = _state.load(std::memory_order_relaxed);
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uint32_t expected = current & (~static_cast<uint32_t>(Flag::locked));
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if (current == expected) {
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uint32_t desired = expected | static_cast<uint32_t>(Flag::locked);
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// try to lock
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bool success = _state.compare_exchange_strong(expected, desired, std::memory_order_acq_rel,
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std::memory_order_relaxed);
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if (success) {
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cb();
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return true;
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}
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}
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attempt++;
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cpu_relax();
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// TODO: exponential back-off for failure?
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}
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return false;
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}
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void BucketState::unlock() {
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TRI_ASSERT(isLocked());
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_state.fetch_and(~static_cast<uint32_t>(Flag::locked), std::memory_order_release);
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}
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bool BucketState::isSet(BucketState::Flag flag) const {
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TRI_ASSERT(isLocked());
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return ((_state.load() & static_cast<uint32_t>(flag)) > 0);
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}
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bool BucketState::isSet(BucketState::Flag flag1, BucketState::Flag flag2) const {
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TRI_ASSERT(isLocked());
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return ((_state.load() &
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(static_cast<uint32_t>(flag1) | static_cast<uint32_t>(flag2))) > 0);
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}
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void BucketState::toggleFlag(BucketState::Flag flag) {
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TRI_ASSERT(isLocked());
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_state ^= static_cast<uint32_t>(flag);
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}
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void BucketState::clear() {
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TRI_ASSERT(isLocked());
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_state = static_cast<uint32_t>(Flag::locked);
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}
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