Roll forward to cl/338482889

Signed-off-by: Alexey Polyudov <apolyudov@google.com>
Change-Id: I9850950db8bd84f0904ea1a413151887f52098cf

cpp/platform/impl/g3/multi_thread_executor.h

@@ -0,0 +1,59 @@
+#ifndef PLATFORM_IMPL_G3_MULTI_THREAD_EXECUTOR_H_
+#define PLATFORM_IMPL_G3_MULTI_THREAD_EXECUTOR_H_
+
+#include <atomic>
+
+#include "platform/api/submittable_executor.h"
+#include "platform/impl/g3/count_down_latch.h"
+#include "absl/time/clock.h"
+#include "thread/threadpool.h"
+
+namespace location {
+namespace nearby {
+namespace g3 {
+
+// An Executor that reuses a fixed number of threads operating off a shared
+// unbounded queue.
+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 ? 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 g3
+}  // namespace nearby
+}  // namespace location
+
+#endif  // PLATFORM_IMPL_G3_MULTI_THREAD_EXECUTOR_H_