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diff --git a/third_party/abseil-cpp/absl/strings/internal/cordz_update_tracker.h b/third_party/abseil-cpp/absl/strings/internal/cordz_update_tracker.h
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+// 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 {
+    kUnknown,
+    kAppendBuffer,
+    kAppendCord,
+    kAppendExternalMemory,
+    kAppendString,
+    kAssignCord,
+    kAssignString,
+    kClear,
+    kConstructorCord,
+    kConstructorString,
+    kCordReader,
+    kFlatten,
+    kGetAppendRegion,
+    kMakeCordFromExternal,
+    kMoveAppendCord,
+    kMoveAssignCord,
+    kMovePrependCord,
+    kPrependBuffer,
+    kPrependCord,
+    kPrependString,
+    kRemovePrefix,
+    kRemoveSuffix,
+    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);
+  }
+
+  // Adds all the values from `src` to this instance
+  void LossyAdd(const CordzUpdateTracker& src) {
+    for (int i = 0; i < kNumMethods; ++i) {
+      MethodIdentifier method = static_cast<MethodIdentifier>(i);
+      if (int64_t value = src.Value(method)) {
+        LossyAdd(method, value);
+      }
+    }
+  }
+
+ private:
+  // Until C++20 std::atomic is not constexpr default-constructible, so we need
+  // a wrapper for this class to be constexpr constructible.
+  class Counter : public std::atomic<int64_t> {
+   public:
+    constexpr Counter() noexcept : std::atomic<int64_t>(0) {}
+  };
+
+  Counter values_[kNumMethods];
+};
+
+}  // namespace cord_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_STRINGS_INTERNAL_CORDZ_UPDATE_TRACKER_H_