Delete the windows specific count_down_latch and use the shared implementation

PiperOrigin-RevId: 398772515

cpp/platform/impl/shared/count_down_latch.h

@@ -0,0 +1,53 @@
+// Copyright 2020 Google LLC
+//
+// 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 PLATFORM_IMPL_SHARED_COUNT_DOWN_LATCH_H_
+#define PLATFORM_IMPL_SHARED_COUNT_DOWN_LATCH_H_
+
+#include "absl/base/thread_annotations.h"
+#include "absl/synchronization/mutex.h"
+#include "absl/time/clock.h"
+#include "platform/api/count_down_latch.h"
+
+namespace location {
+namespace nearby {
+namespace shared {
+
+// A synchronization aid that allows one or more threads to wait until a set of
+// operations being performed in other threads completes.
+//
+// https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/CountDownLatch.html
+class CountDownLatch final : public api::CountDownLatch {
+ public:
+  explicit CountDownLatch(int count);
+  CountDownLatch(const CountDownLatch&) = delete;
+  CountDownLatch& operator=(const CountDownLatch&) = delete;
+  CountDownLatch(CountDownLatch&&) = delete;
+  CountDownLatch& operator=(CountDownLatch&&) = delete;
+  ExceptionOr<bool> Await(absl::Duration timeout) override;
+  Exception Await() override;
+  void CountDown() override;
+
+ private:
+  absl::Mutex mutex_;   // Mutex to be used with cond_.Wait...() method family.
+  absl::CondVar cond_;  // Condition to synchronize up to N waiting threads.
+  int count_
+      ABSL_GUARDED_BY(mutex_);  // When zero, latch should release all waiters.
+};
+
+}  // namespace shared
+}  // namespace nearby
+}  // namespace location
+
+#endif  // PLATFORM_IMPL_G3_COUNT_DOWN_LATCH_H_