Add an implementation of Waiter that uses std::mutex/std::condition_variable

This implementation may at some point become the default on some
platforms.  Currently not all platforms have widespread support for
both real absolute timeouts or real relative timeouts (here "real"
means without converting to the other timeout type which is the only
one supported by the underlying APIs). In this case we can defer to
their standard library to implement correct support.

This is not currently the default on any platform

Note: The size of WaiterState had to increase to fit the new implementation
PiperOrigin-RevId: 518266646
Change-Id: I7f246646a960d6e1b155f9de0bf2f681c5d3d245

1 files changed, 56 insertions, 0 deletions

diff --git a/absl/synchronization/internal/stdcpp_waiter.h b/absl/synchronization/internal/stdcpp_waiter.h
new file mode 100644
index 00000000..e592a27b
--- /dev/null
+++ b/absl/synchronization/internal/stdcpp_waiter.h
@@ -0,0 +1,56 @@
+// Copyright 2023 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_SYNCHRONIZATION_INTERNAL_STDCPP_WAITER_H_
+#define ABSL_SYNCHRONIZATION_INTERNAL_STDCPP_WAITER_H_
+
+#include <condition_variable>  // NOLINT(build/c++11)
+#include <mutex>  // NOLINT(build/c++11)
+
+#include "absl/base/config.h"
+#include "absl/synchronization/internal/kernel_timeout.h"
+#include "absl/synchronization/internal/waiter_base.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace synchronization_internal {
+
+#define ABSL_INTERNAL_HAVE_STDCPP_WAITER 1
+
+class StdcppWaiter : public WaiterCrtp<StdcppWaiter> {
+ public:
+  StdcppWaiter();
+
+  bool Wait(KernelTimeout t);
+  void Post();
+  void Poke();
+
+  static constexpr char kName[] = "StdcppWaiter";
+
+ private:
+  // REQUIRES: mu_ must be held.
+  void InternalCondVarPoke();
+
+  std::mutex mu_;
+  std::condition_variable cv_;
+  int waiter_count_;
+  int wakeup_count_;  // Unclaimed wakeups.
+};
+
+}  // namespace synchronization_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_SYNCHRONIZATION_INTERNAL_STDCPP_WAITER_H_