Roll forward to cl/338482889

Signed-off-by: Alexey Polyudov <apolyudov@google.com>
Change-Id: Ic2bdb234e89f3c5860d1b483dd4bce689f13d057

cpp/platform/public/settable_future.h

@@ -0,0 +1,128 @@
+// 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_PUBLIC_SETTABLE_FUTURE_H_
+#define PLATFORM_PUBLIC_SETTABLE_FUTURE_H_
+
+#include <utility>
+
+#include "platform/public/condition_variable.h"
+#include "platform/public/mutex.h"
+#include "platform/public/mutex_lock.h"
+#include "platform/public/system_clock.h"
+
+namespace location {
+namespace nearby {
+
+template <typename T>
+class SettableFuture : public api::SettableFuture<T> {
+ public:
+  SettableFuture() = default;
+  ~SettableFuture() override = default;
+
+  bool Set(T value) override {
+    MutexLock lock(&mutex_);
+    if (!done_) {
+      value_ = std::move(value);
+      done_ = true;
+      exception_ = {Exception::kSuccess};
+      completed_.Notify();
+      InvokeAllLocked();
+      return true;
+    }
+    return false;
+  }
+
+  void AddListener(Runnable runnable, api::Executor* executor) override {
+    MutexLock lock(&mutex_);
+    if (done_) {
+      executor->Execute(std::move(runnable));
+    } else {
+      listeners_.emplace_back(std::make_pair(executor, std::move(runnable)));
+    }
+  }
+
+  bool IsSet() const {
+    MutexLock lock(&mutex_);
+    return done_;
+  }
+
+  bool SetException(Exception exception) override {
+    MutexLock lock(&mutex_);
+    return SetExceptionLocked(exception);
+  }
+
+  ExceptionOr<T> Get() override {
+    MutexLock lock(&mutex_);
+    while (!done_) {
+      completed_.Wait();
+    }
+    return exception_.value != Exception::kSuccess
+               ? ExceptionOr<T>{exception_.value}
+               : ExceptionOr<T>{value_};
+  }
+
+  ExceptionOr<T> Get(absl::Duration timeout) override {
+    MutexLock lock(&mutex_);
+    while (!done_) {
+      absl::Time start_time = SystemClock::ElapsedRealtime();
+      if (completed_.Wait(timeout).Raised(Exception::kInterrupted)) {
+        SetExceptionLocked({Exception::kInterrupted});
+        break;
+      }
+      absl::Duration spent = SystemClock::ElapsedRealtime() - start_time;
+      if (spent < timeout) {
+        timeout -= spent;
+      } else if (!done_) {
+        SetExceptionLocked({Exception::kTimeout});
+        break;
+      }
+    }
+    return exception_.value != Exception::kSuccess
+               ? ExceptionOr<T>{exception_.value}
+               : ExceptionOr<T>{value_};
+  }
+
+ private:
+  bool SetExceptionLocked(Exception exception) {
+    if (!done_) {
+      exception_ = exception.value != Exception::kSuccess
+                       ? exception
+                       : Exception{Exception::kFailed};
+      done_ = true;
+      completed_.Notify();
+      InvokeAllLocked();
+    }
+    return true;
+  }
+
+  void InvokeAllLocked() {
+    for (auto& item : listeners_) {
+      item.first->Execute(std::move(item.second));
+    }
+    listeners_.clear();
+  }
+
+  mutable Mutex mutex_;
+  ConditionVariable completed_{&mutex_};
+  std::vector<std::pair<api::Executor*, std::function<void()>>> listeners_;
+  bool done_{false};
+  T value_;
+  Exception exception_{Exception::kFailed};
+};
+
+}  // namespace nearby
+}  // namespace location
+
+#endif  // PLATFORM_PUBLIC_SETTABLE_FUTURE_H_