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+/*
+ *  Copyright 2018 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef P2P_BASE_REGATHERING_CONTROLLER_H_
+#define P2P_BASE_REGATHERING_CONTROLLER_H_
+
+#include <memory>
+
+#include "api/task_queue/pending_task_safety_flag.h"
+#include "p2p/base/ice_transport_internal.h"
+#include "p2p/base/port_allocator.h"
+#include "rtc_base/thread.h"
+
+namespace webrtc {
+
+// Controls regathering of candidates for the ICE transport passed into it,
+// reacting to signals like SignalWritableState, SignalNetworkRouteChange, etc.,
+// using methods like GetStats to get additional information, and calling
+// methods like RegatherOnFailedNetworks on the PortAllocatorSession when
+// regathering is desired.
+//
+// "Regathering" is defined as gathering additional candidates within a single
+// ICE generation (or in other words, PortAllocatorSession), and is possible
+// when "continual gathering" is enabled. This may allow connectivity to be
+// maintained and/or restored without a full ICE restart.
+//
+// Regathering will only begin after PortAllocationSession is set via
+// set_allocator_session. This should be called any time the "active"
+// PortAllocatorSession is changed (in other words, when an ICE restart occurs),
+// so that candidates are gathered for the "current" ICE generation.
+//
+// All methods of BasicRegatheringController should be called on the same
+// thread as the one passed to the constructor, and this thread should be the
+// same one where PortAllocatorSession runs, which is also identical to the
+// network thread of the ICE transport, as given by
+// P2PTransportChannel::thread().
+class BasicRegatheringController : public sigslot::has_slots<> {
+ public:
+  struct Config {
+    int regather_on_failed_networks_interval =
+        cricket::REGATHER_ON_FAILED_NETWORKS_INTERVAL;
+  };
+
+  BasicRegatheringController() = delete;
+  BasicRegatheringController(const Config& config,
+                             cricket::IceTransportInternal* ice_transport,
+                             rtc::Thread* thread);
+  ~BasicRegatheringController() override;
+  // TODO(qingsi): Remove this method after implementing a new signal in
+  // P2PTransportChannel and reacting to that signal for the initial schedules
+  // of regathering.
+  void Start();
+  void set_allocator_session(cricket::PortAllocatorSession* allocator_session) {
+    allocator_session_ = allocator_session;
+  }
+  // Setting a different config of the regathering interval range on all
+  // networks cancels and reschedules the recurring schedules, if any, of
+  // regathering on all networks. The same applies to the change of the
+  // regathering interval on the failed networks. This rescheduling behavior is
+  // seperately defined for the two config parameters.
+  void SetConfig(const Config& config);
+
+ private:
+  // TODO(qingsi): Implement the following methods and use methods from the ICE
+  // transport like GetStats to get additional information for the decision
+  // making in regathering.
+  void OnIceTransportStateChanged(cricket::IceTransportInternal*) {}
+  void OnIceTransportWritableState(rtc::PacketTransportInternal*) {}
+  void OnIceTransportReceivingState(rtc::PacketTransportInternal*) {}
+  void OnIceTransportNetworkRouteChanged(absl::optional<rtc::NetworkRoute>) {}
+  // Schedules delayed and repeated regathering of local candidates on failed
+  // networks, where the delay in milliseconds is given by the config. Each
+  // repetition is separated by the same delay. When scheduled, all previous
+  // schedules are canceled.
+  void ScheduleRecurringRegatheringOnFailedNetworks();
+  // Cancels regathering scheduled by ScheduleRecurringRegatheringOnAllNetworks.
+  void CancelScheduledRecurringRegatheringOnAllNetworks();
+
+  // We use a flag to be able to cancel pending regathering operations when
+  // the object goes out of scope or the config changes.
+  std::unique_ptr<ScopedTaskSafety> pending_regathering_;
+  Config config_;
+  cricket::IceTransportInternal* ice_transport_;
+  cricket::PortAllocatorSession* allocator_session_ = nullptr;
+  rtc::Thread* const thread_;
+};
+
+}  // namespace webrtc
+
+#endif  // P2P_BASE_REGATHERING_CONTROLLER_H_