124 lines
3.8 KiB
C
124 lines
3.8 KiB
C
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// Copyright 2021 The Abseil Authors
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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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// https://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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#ifndef ABSL_STRINGS_INTERNAL_CORDZ_UPDATE_TRACKER_H_
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#define ABSL_STRINGS_INTERNAL_CORDZ_UPDATE_TRACKER_H_
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#include <atomic>
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#include <cstdint>
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#include "absl/base/config.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace cord_internal {
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// CordzUpdateTracker tracks counters for Cord update methods.
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//
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// The purpose of CordzUpdateTracker is to track the number of calls to methods
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// updating Cord data for sampled cords. The class internally uses 'lossy'
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// atomic operations: Cord is thread-compatible, so there is no need to
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// synchronize updates. However, Cordz collection threads may call 'Value()' at
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// any point, so the class needs to provide thread safe access.
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//
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// This class is thread-safe. But as per above comments, all non-const methods
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// should be used single-threaded only: updates are thread-safe but lossy.
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class CordzUpdateTracker {
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public:
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// Tracked update methods.
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enum MethodIdentifier {
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kUnknown,
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kAppendCord,
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kAppendCordBuffer,
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kAppendExternalMemory,
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kAppendString,
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kAssignCord,
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kAssignString,
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kClear,
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kConstructorCord,
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kConstructorString,
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kCordReader,
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kFlatten,
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kGetAppendBuffer,
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kGetAppendRegion,
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kMakeCordFromExternal,
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kMoveAppendCord,
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kMoveAssignCord,
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kMovePrependCord,
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kPrependCord,
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kPrependCordBuffer,
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kPrependString,
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kRemovePrefix,
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kRemoveSuffix,
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kSetExpectedChecksum,
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kSubCord,
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// kNumMethods defines the number of entries: must be the last entry.
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kNumMethods,
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};
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// Constructs a new instance. All counters are zero-initialized.
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constexpr CordzUpdateTracker() noexcept : values_{} {}
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// Copy constructs a new instance.
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CordzUpdateTracker(const CordzUpdateTracker& rhs) noexcept { *this = rhs; }
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// Assigns the provided value to this instance.
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CordzUpdateTracker& operator=(const CordzUpdateTracker& rhs) noexcept {
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for (int i = 0; i < kNumMethods; ++i) {
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values_[i].store(rhs.values_[i].load(std::memory_order_relaxed),
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std::memory_order_relaxed);
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}
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return *this;
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}
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// Returns the value for the specified method.
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int64_t Value(MethodIdentifier method) const {
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return values_[method].load(std::memory_order_relaxed);
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}
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// Increases the value for the specified method by `n`
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void LossyAdd(MethodIdentifier method, int64_t n = 1) {
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auto& value = values_[method];
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value.store(value.load(std::memory_order_relaxed) + n,
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std::memory_order_relaxed);
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}
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// Adds all the values from `src` to this instance
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void LossyAdd(const CordzUpdateTracker& src) {
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for (int i = 0; i < kNumMethods; ++i) {
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MethodIdentifier method = static_cast<MethodIdentifier>(i);
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if (int64_t value = src.Value(method)) {
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LossyAdd(method, value);
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}
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}
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}
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private:
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// Until C++20 std::atomic is not constexpr default-constructible, so we need
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// a wrapper for this class to be constexpr constructible.
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class Counter : public std::atomic<int64_t> {
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public:
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constexpr Counter() noexcept : std::atomic<int64_t>(0) {}
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};
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Counter values_[kNumMethods];
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};
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} // namespace cord_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_STRINGS_INTERNAL_CORDZ_UPDATE_TRACKER_H_
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