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diff --git a/Firestore/core/src/firebase/firestore/util/executor_libdispatch.h b/Firestore/core/src/firebase/firestore/util/executor_libdispatch.h
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+/*
+ * Copyright 2018 Google
+ *
+ * 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
+ *
+ *      http://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 FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_EXECUTOR_LIBDISPATCH_H_
+#define FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_EXECUTOR_LIBDISPATCH_H_
+
+#include <chrono>  // NOLINT(build/c++11)
+#include <functional>
+#include <memory>
+#include <string>
+#include <utility>
+#include <vector>
+#include "dispatch/dispatch.h"
+
+#include "Firestore/core/src/firebase/firestore/util/executor.h"
+#include "Firestore/core/src/firebase/firestore/util/firebase_assert.h"
+#include "absl/strings/string_view.h"
+
+#if !defined(__OBJC__)
+// `dispatch_queue_t` gets defined to different types when compiled in C++ or
+// Objective-C mode. Source files including this header should all be compiled
+// in the same mode to avoid linker errors.
+#error "This header only supports Objective-C++ (see comment for more info)."
+#endif  // !defined(__OBJC__)
+
+namespace firebase {
+namespace firestore {
+namespace util {
+
+namespace internal {
+
+// Generic wrapper over `dispatch_async_f`, providing `dispatch_async`-like
+// interface: accepts an arbitrary invocable object in place of an Objective-C
+// block.
+void DispatchAsync(dispatch_queue_t queue, std::function<void()>&& work);
+
+// Similar to `DispatchAsync` but wraps `dispatch_sync_f`.
+void DispatchSync(dispatch_queue_t queue, std::function<void()> work);
+
+class TimeSlot;
+
+// A serial queue built on top of libdispatch. The operations are run on
+// a dedicated serial dispatch queue.
+class ExecutorLibdispatch : public Executor {
+ public:
+  explicit ExecutorLibdispatch(dispatch_queue_t dispatch_queue);
+
+  bool IsCurrentExecutor() const override;
+  std::string CurrentExecutorName() const override;
+  std::string Name() const override;
+
+  void Execute(Operation&& operation) override;
+  void ExecuteBlocking(Operation&& operation) override;
+  DelayedOperation Schedule(Milliseconds delay,
+                            TaggedOperation&& operation) override;
+
+  void RemoveFromSchedule(const TimeSlot* to_remove);
+
+  bool IsScheduled(Tag tag) const override;
+  absl::optional<TaggedOperation> PopFromSchedule() override;
+
+  dispatch_queue_t dispatch_queue() const {
+    return dispatch_queue_;
+  }
+
+ private:
+  dispatch_queue_t dispatch_queue_;
+  // Stores non-owned pointers to `TimeSlot`s.
+  // Invariant: if a `TimeSlot` is in `schedule_`, it's a valid pointer.
+  std::vector<TimeSlot*> schedule_;
+};
+
+}  // namespace internal
+}  // namespace util
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_SRC_FIREBASE_FIRESTORE_UTIL_EXECUTOR_LIBDISPATCH_H_