Roll forward to cl/338482889

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

cpp/platform/impl/ios/multi_thread_executor.h

@@ -0,0 +1,71 @@
+// 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_IOS_MULTI_THREAD_EXECUTOR_H_
+#define PLATFORM_IMPL_IOS_MULTI_THREAD_EXECUTOR_H_
+
+#include <atomic>
+
+#include "platform/api/submittable_executor.h"
+#include "platform/impl/ios/count_down_latch.h"
+#include "absl/time/clock.h"
+#include "thread/threadpool.h"
+
+namespace location {
+namespace nearby {
+namespace ios {
+
+class MultiThreadExecutor : public api::SubmittableExecutor {
+ public:
+  explicit MultiThreadExecutor(int max_parallelism)
+      : thread_pool_(max_parallelism) {
+    thread_pool_.StartWorkers();
+  }
+  void Execute(Runnable&& runnable) override {
+    if (!shutdown_) {
+      thread_pool_.Schedule(std::move(runnable));
+    }
+  }
+  bool DoSubmit(Runnable&& runnable) override {
+    if (shutdown_) return false;
+    thread_pool_.Schedule(std::move(runnable));
+    return true;
+  }
+  void Shutdown() override { DoShutdown(); }
+  ~MultiThreadExecutor() override { DoShutdown(); }
+
+  int GetTid(int index) const override {
+    const auto* thread = thread_pool_.thread(index);
+    return thread ? *(int*)(thread->tid()) : 0;
+  }
+
+  void ScheduleAfter(absl::Duration delay, Runnable&& runnable) {
+    if (shutdown_) return;
+    thread_pool_.ScheduleAt(absl::Now() + delay, std::move(runnable));
+  }
+  bool InShutdown() const { return shutdown_; }
+
+ private:
+  void DoShutdown() {
+    shutdown_ = true;
+  }
+  std::atomic_bool shutdown_ = false;
+  ThreadPool thread_pool_;
+};
+
+}  // namespace ios
+}  // namespace nearby
+}  // namespace location
+
+#endif  // PLATFORM_IMPL_IOS_MULTI_THREAD_EXECUTOR_H_