mirror of https://gitee.com/bigwinds/arangodb
135 lines
5.8 KiB
C++
135 lines
5.8 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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#ifndef ARANGODB_CACHE_BUCKET_STATE_H
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#define ARANGODB_CACHE_BUCKET_STATE_H
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#include "Basics/Common.h"
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#include <atomic>
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#include <cstdint>
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namespace arangodb {
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namespace cache {
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////////////////////////////////////////////////////////////////////////////////
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/// @brief Simple state class with a small footprint.
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///
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/// Underlying store is simply a std::atomic<uint32_t>, and each bit corresponds
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/// to a flag that can be set. The lowest bit is special and is designated as
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/// the locking flag. Any access (read or modify) to the state must occur when
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/// the state is already locked; the two exceptions are to check whether the
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/// state is locked and, of course, to lock it. Any flags besides the lock flag
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/// are treated uniformly, and can be checked or toggled. Each flag is defined
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/// via an enum and must correspond to exactly one set bit.
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////////////////////////////////////////////////////////////////////////////////
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struct BucketState {
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typedef std::function<void()> CallbackType;
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//////////////////////////////////////////////////////////////////////////////
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/// @brief Flags which can be queried or toggled to reflect state.
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///
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/// Each flag must have exactly one bit set, fit in uint32_t. The 'locked'
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/// flag is special and should remain the least-significant bit. When other
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/// flags are added,they should be kept in alphabetical order for readability,
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/// and all flag values should be adjusted to keep bit-significance in
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/// ascending order.
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//////////////////////////////////////////////////////////////////////////////
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enum class Flag : uint32_t {
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locked = 0x00000001,
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blacklisted = 0x00000002,
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disabled = 0x00000004,
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evictions = 0x00000008,
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migrated = 0x00000010,
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migrating = 0x00000020,
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rebalancing = 0x00000040,
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resizing = 0x00000080,
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shutdown = 0x00000100,
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shuttingDown = 0x00000200,
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};
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//////////////////////////////////////////////////////////////////////////////
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/// @brief Initializes state with no flags set and unlocked
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//////////////////////////////////////////////////////////////////////////////
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BucketState();
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//////////////////////////////////////////////////////////////////////////////
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/// @brief Initializes state to match another
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//////////////////////////////////////////////////////////////////////////////
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BucketState(BucketState const& other);
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//////////////////////////////////////////////////////////////////////////////
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/// @brief Initializes state to match another
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//////////////////////////////////////////////////////////////////////////////
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BucketState& operator=(BucketState const& other);
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//////////////////////////////////////////////////////////////////////////////
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/// @brief Checks if state is locked.
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//////////////////////////////////////////////////////////////////////////////
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bool isLocked() const;
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//////////////////////////////////////////////////////////////////////////////
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/// @brief Used to lock state. Returns true if locked, false otherwise.
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///
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/// By default, it will try as many times as necessary to acquire the lock.
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/// The number of tries may be limited to any positive integer value to avoid
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/// excessively long waits. The return value indicates whether the state was
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/// locked or not. The optional second parameter is a function which will be
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/// called upon successfully locking the state.
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//////////////////////////////////////////////////////////////////////////////
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bool lock(uint64_t maxTries = UINT64_MAX, BucketState::CallbackType cb = []() -> void {});
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//////////////////////////////////////////////////////////////////////////////
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/// @brief Unlocks the state. Requires state to be locked.
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//////////////////////////////////////////////////////////////////////////////
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void unlock();
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//////////////////////////////////////////////////////////////////////////////
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/// @brief Checks whether the given flag is set. Requires state to be locked.
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//////////////////////////////////////////////////////////////////////////////
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bool isSet(BucketState::Flag flag) const;
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bool isSet(BucketState::Flag flag1, BucketState::Flag flag2) const;
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//////////////////////////////////////////////////////////////////////////////
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/// @brief Toggles the given flag. Requires state to be locked.
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//////////////////////////////////////////////////////////////////////////////
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void toggleFlag(BucketState::Flag flag);
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//////////////////////////////////////////////////////////////////////////////
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/// @brief Unsets all flags besides Flag::locked. Requires state to be locked.
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//////////////////////////////////////////////////////////////////////////////
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void clear();
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private:
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std::atomic<uint32_t> _state;
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};
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// ensure that state is exactly the size of uint32_t
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static_assert(sizeof(BucketState) == sizeof(uint32_t),
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"Expected sizeof(BucketState) == sizeof(uint32_t).");
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}; // end namespace cache
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}; // end namespace arangodb
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#endif
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