Squashed 'third_party/abseil/' content from commit ddf8e52a2
Change-Id: I330cdc687395c6605ad027b855e313ff4a2059e9
git-subtree-dir: third_party/abseil
git-subtree-split: ddf8e52a2918dd0ccec75d3e2426125fa3926724
diff --git a/absl/flags/flag.cc b/absl/flags/flag.cc
new file mode 100644
index 0000000..a02d069
--- /dev/null
+++ b/absl/flags/flag.cc
@@ -0,0 +1,60 @@
+//
+// Copyright 2019 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/flags/flag.h"
+
+#include <cstring>
+
+namespace absl {
+
+// We want to validate the type mismatch between type definition and
+// declaration. The lock-free implementation does not allow us to do it,
+// so in debug builds we always use the slower implementation, which always
+// validates the type.
+#ifndef NDEBUG
+#define ABSL_FLAGS_ATOMIC_GET(T) \
+ T GetFlag(const absl::Flag<T>& flag) { return flag.Get(); }
+#else
+#define ABSL_FLAGS_ATOMIC_GET(T) \
+ T GetFlag(const absl::Flag<T>& flag) { \
+ T result; \
+ if (flag.AtomicGet(&result)) { \
+ return result; \
+ } \
+ return flag.Get(); \
+ }
+#endif
+
+ABSL_FLAGS_INTERNAL_FOR_EACH_LOCK_FREE(ABSL_FLAGS_ATOMIC_GET)
+
+#undef ABSL_FLAGS_ATOMIC_GET
+
+// This global nutex protects on-demand construction of flag objects in MSVC
+// builds.
+#if defined(_MSC_VER)
+
+namespace flags_internal {
+
+ABSL_CONST_INIT static absl::Mutex construction_guard(absl::kConstInit);
+
+void LockGlobalConstructionGuard() { construction_guard.Lock(); }
+
+void UnlockGlobalConstructionGuard() { construction_guard.Unlock(); }
+
+} // namespace flags_internal
+
+#endif
+
+} // namespace absl