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Diffstat (limited to 'absl/strings/internal/cordz_update_tracker.h')
-rw-r--r-- | absl/strings/internal/cordz_update_tracker.h | 96 |
1 files changed, 96 insertions, 0 deletions
diff --git a/absl/strings/internal/cordz_update_tracker.h b/absl/strings/internal/cordz_update_tracker.h new file mode 100644 index 00000000..3c617e93 --- /dev/null +++ b/absl/strings/internal/cordz_update_tracker.h @@ -0,0 +1,96 @@ +// Copyright 2021 The Abseil Authors +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// https://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. + +#ifndef ABSL_STRINGS_INTERNAL_CORDZ_UPDATE_TRACKER_H_ +#define ABSL_STRINGS_INTERNAL_CORDZ_UPDATE_TRACKER_H_ + +#include <atomic> +#include <cstdint> + +#include "absl/base/config.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace cord_internal { + +// CordzUpdateTracker tracks counters for Cord update methods. +// +// The purpose of CordzUpdateTracker is to track the number of calls to methods +// updating Cord data for sampled cords. The class internally uses 'lossy' +// atomic operations: Cord is thread-compatible, so there is no need to +// synchronize updates. However, Cordz collection threads may call 'Value()' at +// any point, so the class needs to provide thread safe access. +// +// This class is thread-safe. But as per above comments, all non-const methods +// should be used single-threaded only: updates are thread-safe but lossy. +class CordzUpdateTracker { + public: + // Tracked update methods. + enum MethodIdentifier { + kAssignString, + kAssignCord, + kMoveAssignCord, + kAppendString, + kAppendCord, + kMoveAppendCord, + kPrependString, + kPrependCord, + kMovePrependCord, + kAppendExternalMemory, + kFlatten, + kGetAppendRegion, + kRemovePrefix, + kRemoveSuffic, + kSubCord, + + // kNumMethods defines the number of entries: must be the last entry. + kNumMethods, + }; + + // Constructs a new instance. All counters are zero-initialized. + constexpr CordzUpdateTracker() noexcept : values_{} {} + + // Copy constructs a new instance. + CordzUpdateTracker(const CordzUpdateTracker& rhs) noexcept { *this = rhs; } + + // Assigns the provided value to this instance. + CordzUpdateTracker& operator=(const CordzUpdateTracker& rhs) noexcept { + for (int i = 0; i < kNumMethods; ++i) { + values_[i].store(rhs.values_[i].load(std::memory_order_relaxed), + std::memory_order_relaxed); + } + return *this; + } + + // Returns the value for the specified method. + int64_t Value(MethodIdentifier method) const { + return values_[method].load(std::memory_order_relaxed); + } + + // Increases the value for the specified method by `n` + void LossyAdd(MethodIdentifier method, int64_t n = 1) { + auto& value = values_[method]; + value.store(value.load(std::memory_order_relaxed) + n, + std::memory_order_relaxed); + } + + private: + std::atomic<int64_t> values_[kNumMethods]; +}; + +} // namespace cord_internal +ABSL_NAMESPACE_END +} // namespace absl + +#endif // ABSL_STRINGS_INTERNAL_CORDZ_UPDATE_TRACKER_H_ |