Synchronization: Refactor Waiter to allow us to write tests

Instead of being only able to test the platform Waiter implementation,
this allows us to be able to test all Waiter implementations that
build on a specific platform.

A unittest is added that tests all implementations that work for the
platform, and allows us to check that the expected one is being used
by printing the name of the selected implementation.

PiperOrigin-RevId: 518072415
Change-Id: Ie9e6fcd9d8283b4038e6f4e68a304d2adcc04b19

1 files changed, 70 insertions, 0 deletions

diff --git a/absl/synchronization/internal/win32_waiter.h b/absl/synchronization/internal/win32_waiter.h
new file mode 100644
index 00000000..87eb617c
--- /dev/null
+++ b/absl/synchronization/internal/win32_waiter.h
@@ -0,0 +1,70 @@
+// 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_WIN32_WAITER_H_
+#define ABSL_SYNCHRONIZATION_INTERNAL_WIN32_WAITER_H_
+
+#ifdef _WIN32
+#include <sdkddkver.h>
+#endif
+
+#if defined(_WIN32) && _WIN32_WINNT >= _WIN32_WINNT_VISTA
+
+#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_WIN32_WAITER 1
+
+class Win32Waiter : public WaiterCrtp<Win32Waiter> {
+ public:
+  Win32Waiter();
+
+  bool Wait(KernelTimeout t);
+  void Post();
+  void Poke();
+
+  static constexpr char kName[] = "Win32Waiter";
+
+ private:
+  // WinHelper - Used to define utilities for accessing the lock and
+  // condition variable storage once the types are complete.
+  class WinHelper;
+
+  // REQUIRES: WinHelper::GetLock(this) must be held.
+  void InternalCondVarPoke();
+
+  // We can't include Windows.h in our headers, so we use aligned character
+  // buffers to define the storage of SRWLOCK and CONDITION_VARIABLE.
+  // SRW locks and condition variables do not need to be explicitly destroyed.
+  // https://docs.microsoft.com/en-us/windows/win32/api/synchapi/nf-synchapi-initializesrwlock
+  // https://stackoverflow.com/questions/28975958/why-does-windows-have-no-deleteconditionvariable-function-to-go-together-with
+  alignas(void*) unsigned char mu_storage_[sizeof(void*)];
+  alignas(void*) unsigned char cv_storage_[sizeof(void*)];
+  int waiter_count_;
+  int wakeup_count_;
+};
+
+}  // namespace synchronization_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // defined(_WIN32) && _WIN32_WINNT >= _WIN32_WINNT_VISTA
+
+#endif  // ABSL_SYNCHRONIZATION_INTERNAL_WIN32_WAITER_H_