Export of internal Abseil changes

--
5ff0c4b38386ae80b25e9f8d0e1bac07fd7ce92c by Martijn Vels <mvels@google.com>:

Add CordzUpdateTracker class

PiperOrigin-RevId: 368469046

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4de916b1ba4b5480b4dbe93d28c5eaa110449c66 by Derek Mauro <dmauro@google.com>:

Adds `ABSL_ATTRIBUTE_LIFETIME_BOUND` to `absl::Span`s initializer_list
constructor.

Compilers that support this attribute will emit a warning
if the parameter does not have sufficient lifetime.

For more information, see
https://github.com/abseil/abseil-cpp/blob/b97a1ecda869ca8754d467a56c50275cebfeb328/absl/types/span.h#L209-L248

PiperOrigin-RevId: 368429085

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bb6669016412bf5afffc02d0818a66dfe1c524cf by Martijn Vels <mvels@google.com>:

Reorganize internal cord code in CMakeLists.txt into cord_internal library

PiperOrigin-RevId: 368423765

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d1d7fce066172d5fcfa0310c4e27631d895d7e50 by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 368346725
GitOrigin-RevId: 5ff0c4b38386ae80b25e9f8d0e1bac07fd7ce92c
Change-Id: Ic4627eab4f0274e400a6d12cde3341fb538de075

1 files changed, 130 insertions, 0 deletions

diff --git a/absl/strings/internal/cordz_update_tracker_test.cc b/absl/strings/internal/cordz_update_tracker_test.cc
new file mode 100644
index 0000000..4578204
--- /dev/null
+++ b/absl/strings/internal/cordz_update_tracker_test.cc
@@ -0,0 +1,130 @@
+// 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.
+
+#include "absl/strings/internal/cordz_update_tracker.h"
+
+#include <array>
+#include <thread>  // NOLINT
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/base/attributes.h"
+#include "absl/base/config.h"
+#include "absl/synchronization/notification.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace cord_internal {
+namespace {
+
+using ::testing::AnyOf;
+using ::testing::Eq;
+
+using Method = CordzUpdateTracker::MethodIdentifier;
+using Methods = std::array<Method, Method::kNumMethods>;
+
+// Returns an array of all methods defined in `MethodIdentifier`
+Methods AllMethods() {
+  return Methods{Method::kAssignString,    Method::kAssignCord,
+                 Method::kMoveAssignCord,  Method::kAppendString,
+                 Method::kAppendCord,      Method::kMoveAppendCord,
+                 Method::kPrependString,   Method::kPrependCord,
+                 Method::kMovePrependCord, Method::kAppendExternalMemory,
+                 Method::kFlatten,         Method::kGetAppendRegion,
+                 Method::kRemovePrefix,    Method::kRemoveSuffic,
+                 Method::kSubCord};
+}
+
+TEST(CordzUpdateTracker, IsConstExprAndInitializesToZero) {
+  constexpr CordzUpdateTracker tracker;
+  for (Method method : AllMethods()) {
+    ASSERT_THAT(tracker.Value(method), Eq(0));
+  }
+}
+
+TEST(CordzUpdateTracker, LossyAdd) {
+  int64_t n = 1;
+  CordzUpdateTracker tracker;
+  for (Method method : AllMethods()) {
+    tracker.LossyAdd(method, n);
+    EXPECT_THAT(tracker.Value(method), Eq(n));
+    n += 2;
+  }
+}
+
+TEST(CordzUpdateTracker, CopyConstructor) {
+  int64_t n = 1;
+  CordzUpdateTracker src;
+  for (Method method : AllMethods()) {
+    src.LossyAdd(method, n);
+    n += 2;
+  }
+
+  n = 1;
+  CordzUpdateTracker tracker(src);
+  for (Method method : AllMethods()) {
+    EXPECT_THAT(tracker.Value(method), Eq(n));
+    n += 2;
+  }
+}
+
+TEST(CordzUpdateTracker, OperatorAssign) {
+  int64_t n = 1;
+  CordzUpdateTracker src;
+  CordzUpdateTracker tracker;
+  for (Method method : AllMethods()) {
+    src.LossyAdd(method, n);
+    n += 2;
+  }
+
+  n = 1;
+  tracker = src;
+  for (Method method : AllMethods()) {
+    EXPECT_THAT(tracker.Value(method), Eq(n));
+    n += 2;
+  }
+}
+
+TEST(CordzUpdateTracker, ThreadSanitizedValueCheck) {
+  absl::Notification done;
+  CordzUpdateTracker tracker;
+
+  std::thread reader([&done, &tracker] {
+    while (!done.HasBeenNotified()) {
+      int n = 1;
+      for (Method method : AllMethods()) {
+        EXPECT_THAT(tracker.Value(method), AnyOf(Eq(n), Eq(0)));
+        n += 2;
+      }
+    }
+    int n = 1;
+    for (Method method : AllMethods()) {
+      EXPECT_THAT(tracker.Value(method), Eq(n));
+      n += 2;
+    }
+  });
+
+  int64_t n = 1;
+  for (Method method : AllMethods()) {
+    tracker.LossyAdd(method, n);
+    n += 2;
+  }
+  done.Notify();
+  reader.join();
+}
+
+}  // namespace
+}  // namespace cord_internal
+ABSL_NAMESPACE_END
+}  // namespace absl