src/system/SystemLayer.h - third_party/github/project-chip/connectedhomeip - Git at Google

 /*
  *
  *    Copyright (c) 2020-2021 Project CHIP Authors
  *    Copyright (c) 2016-2017 Nest Labs, Inc.
  *
  *    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.
  */

 /**
  *    @file
  *      This file contains declarations of the
  *      chip::System::Layer class and its related types, data and
  *      functions.
  */

 #pragma once

 #include <type_traits>
 #include <utility>

 // Include configuration headers
 #include <system/SystemConfig.h>

 #include <lib/core/CHIPCallback.h>

 #include <lib/support/CodeUtils.h>
 #include <lib/support/DLLUtil.h>
 #include <lib/support/LambdaBridge.h>
 #include <system/SystemClock.h>
 #include <system/SystemError.h>
 #include <system/SystemEvent.h>

 #if CHIP_SYSTEM_CONFIG_USE_SOCKETS || CHIP_SYSTEM_CONFIG_USE_NETWORK_FRAMEWORK
 #include <lib/support/IntrusiveList.h>
 #include <system/SocketEvents.h>
 #endif // CHIP_SYSTEM_CONFIG_USE_SOCKETS || CHIP_SYSTEM_USE_NETWORK_FRAMEWORK

 #if CHIP_SYSTEM_CONFIG_USE_DISPATCH
 #include <dispatch/dispatch.h>
 #elif CHIP_SYSTEM_CONFIG_USE_LIBEV
 #include <ev.h>
 #endif // CHIP_SYSTEM_CONFIG_USE_DISPATCH/LIBEV

 namespace chip {
 namespace System {

 class Layer;
 using TimerCompleteCallback = void (*)(Layer * aLayer, void * appState);

 /**
  * This provides access to timers according to the configured event handling model.
  *
  * The abstract class hierarchy is:
  * - Layer: Core timer methods.
  *   - LayerFreeRTOS: Adds methods specific to CHIP_SYSTEM_CONFIG_USING_LWIP and CHIP_SYSTEM_CONFIG_USE_OPEN_THREAD_ENDPOINT.
  *   - LayerSockets: Adds I/O event methods specific to CHIP_SYSTEM_CONFIG_USING_SOCKETS.
  *     - LayerSocketsLoop: Adds methods for event-loop-based implementations.
  *
  * Threading notes:
  *
  * The SDK is not generally thread safe. System::Layer methods should only be called from
  * a single context, or otherwise externally synchronized. For platforms that use a CHIP
  * event loop thread, timer callbacks are invoked on that thread; for platforms that use
  * a CHIP lock, the lock is held.
  */
 class DLL_EXPORT Layer
 {
 public:
     Layer()          = default;
     virtual ~Layer() = default;

     /**
      * Initialize the Layer.
      */
     virtual CHIP_ERROR Init() = 0;

     /**
      * Shut down the Layer.
      *
      * Some other layers hold pointers to System::Layer, so care must be taken
      * to ensure that they are not used after calling Shutdown().
      */
     virtual void Shutdown() = 0;

     /**
      * True if this Layer is initialized. No method on Layer or its abstract descendants, other than this and `Init()`,
      * may be called from general code unless this is true. (Individual Impls may have looser constraints internally.)
      */
     virtual bool IsInitialized() const = 0;

     /**
      * @brief
      *   This method starts a one-shot timer.  This method must be called while in the Matter context (from
      *   the Matter event loop, or while holding the Matter stack lock).
      *
      *   @note
      *       Only a single timer is allowed to be started with the same @a aComplete and @a aAppState
      *       arguments. If called with @a aComplete and @a aAppState identical to an existing timer,
      *       the currently-running timer will first be cancelled.
      *
      *   @param[in]  aDelay             Time before this timer fires.
      *   @param[in]  aComplete          A pointer to the function called when timer expires.
      *   @param[in]  aAppState          A pointer to the application state object used when timer expires.
      *
      *   @return CHIP_NO_ERROR On success.
      *   @return CHIP_ERROR_NO_MEMORY If a timer cannot be allocated.
      *   @return Other Value indicating timer failed to start.
      */
     virtual CHIP_ERROR StartTimer(Clock::Timeout aDelay, TimerCompleteCallback aComplete, void * aAppState) = 0;

     /**
      * @brief
      *   This method extends the timer expiry to the provided aDelay. This method must be called while in the Matter context
      *   (from the Matter event loop, or while holding the Matter stack lock).
      *   aDelay is not added to the Remaining time of the timer. The finish line is pushed back to aDelay.
      *
      *   @note The goal of this method is that the timer remaining time cannot be shrunk and only extended to a new time
      *         If the provided new Delay is smaller than the timer's remaining time, the timer is left untouched.
      *         In the other case the method acts like StartTimer
      *
      *   @param[in]  aDelay             Time before this timer fires.
      *   @param[in]  aComplete          A pointer to the function called when timer expires.
      *   @param[in]  aAppState          A pointer to the application state object used when timer expires.
      *
      *   @return CHIP_NO_ERROR On success.
      *   @return CHIP_ERROR_INVALID_ARGUMENT If the provided aDelay value is 0
      *   @return CHIP_ERROR_NO_MEMORY If a timer cannot be allocated.
      *   @return Other Value indicating timer failed to start.
      */
     virtual CHIP_ERROR ExtendTimerTo(Clock::Timeout aDelay, TimerCompleteCallback aComplete, void * aAppState) = 0;

     /**
      * @brief
      *   This method searches for the timer matching the provided parameters.
      *   and returns whether it is still "running" and waiting to trigger or not.
      *
      *   @note This is used to verify by how long the ExtendTimer method extends the timer, as it may ignore an extension request
      *        if it is shorter than the current timer's remaining time.
      *
      *   @param[in]  onComplete         A pointer to the function called when timer expires.
      *   @param[in]  appState           A pointer to the application state object used when timer expires.
      *
      *   @return True if there is a current timer set to call, at some point in the future, the provided onComplete callback
      *           with the corresponding appState context. False otherwise.
      */
     virtual bool IsTimerActive(TimerCompleteCallback onComplete, void * appState) = 0;

     /**
      * @brief
      *   This method searches for the timer matching the provided parameters
      *   and returns the remaining time left before it expires.
      *   @param[in]  onComplete         A pointer to the function called when timer expires.
      *   @param[in]  appState           A pointer to the application state object used when timer expires.
      *
      *  @return The remaining time left before the timer expires.
      */
     virtual Clock::Timeout GetRemainingTime(TimerCompleteCallback onComplete, void * appState) = 0;

     /**
      * @brief This method cancels a one-shot timer, started earlier through @p StartTimer().  This method must
      *        be called while in the Matter context (from the Matter event loop, or while holding the Matter
      *        stack lock).
      *
      *   @note
      *       The cancellation could fail silently if the timer specified by the combination of the callback
      *       function and application state object couldn't be found.
      *
      *   @param[in]  aOnComplete   A pointer to the callback function used in calling @p StartTimer().
      *   @param[in]  aAppState     A pointer to the application state object used in calling @p StartTimer().
      *
      */
     virtual void CancelTimer(TimerCompleteCallback aOnComplete, void * aAppState) = 0;

     /**
      * @brief
      *   Schedules a `TimerCompleteCallback` to be run as soon as possible in the Matter context.
      *
      *  WARNING: This must only be called when already in the Matter context (from the Matter event loop, or
      *           while holding the Matter stack lock). The `PlatformMgr::ScheduleWork()` equivalent method
      *           is safe to call outside Matter context.
      *
      * @param[in] aComplete     A pointer to a callback function to be called when this timer fires.
      * @param[in] aAppState     A pointer to an application state object to be passed to the callback function as argument.
      *
      * @retval CHIP_ERROR_INCORRECT_STATE   If the System::Layer has not been initialized.
      * @retval CHIP_ERROR_NO_MEMORY         If the SystemLayer cannot allocate a new timer.
      * @retval CHIP_NO_ERROR                On success.
      */
     virtual CHIP_ERROR ScheduleWork(TimerCompleteCallback aComplete, void * aAppState) = 0;

     /**
      * @brief
      *   Schedules a lambda object to be run as soon as possible in the Matter context.
      *
      * This is safe to call from any context and will guarantee execution in Matter context.
      * Note that the Lambda's capture have to fit within `CHIP_CONFIG_LAMBDA_EVENT_SIZE` bytes.
      *
      * @param[in] lambda The Lambda to execute in Matter context.
      *
      * @retval CHIP_NO_ERROR On success.
      * @retval other Platform-specific errors generated indicating the reason for failure.
      */
     template <typename Lambda>
     CHIP_ERROR ScheduleLambda(const Lambda & lambda)
     {
         static_assert(std::is_invocable_v<Lambda>, "lambda argument must be an invocable with no arguments");
         LambdaBridge bridge;
         bridge.Initialize(lambda);
         return ScheduleLambdaBridge(std::move(bridge));
     }

 private:
     CHIP_ERROR ScheduleLambdaBridge(LambdaBridge && bridge);

     // Not copyable
     Layer(const Layer &)             = delete;
     Layer & operator=(const Layer &) = delete;
 };

 #if CHIP_SYSTEM_CONFIG_USE_LWIP || CHIP_SYSTEM_CONFIG_USE_OPEN_THREAD_ENDPOINT

 class LayerFreeRTOS : public Layer
 {
 };

 #endif // CHIP_SYSTEM_CONFIG_USE_LWIP

 #if CHIP_SYSTEM_CONFIG_USE_SOCKETS || CHIP_SYSTEM_CONFIG_USE_NETWORK_FRAMEWORK

 class LayerSockets : public Layer
 {
 public:
     /**
      * Initialize watching for events on a file descriptor.
      *
      * Returns an opaque token through @a tokenOut that must be passed to subsequent operations for this file descriptor.
      * Multiple calls to start watching the same file descriptor will return the same token.
      * StopWatchingSocket() must be called before closing the file descriptor.
      */
     virtual CHIP_ERROR StartWatchingSocket(int fd, SocketWatchToken * tokenOut) = 0;

     /**
      * Register a callback function.
      *
      * The callback will be invoked (with the CHIP stack lock held) when requested event(s) are ready.
      */
     virtual CHIP_ERROR SetCallback(SocketWatchToken token, SocketWatchCallback callback, intptr_t data) = 0;

     /**
      * Request a callback when the associated file descriptor is readable.
      */
     virtual CHIP_ERROR RequestCallbackOnPendingRead(SocketWatchToken token) = 0;

     /**
      * Request a callback when the associated file descriptor is writable.
      */
     virtual CHIP_ERROR RequestCallbackOnPendingWrite(SocketWatchToken token) = 0;

     /**
      * Cancel a request for a callback when the associated file descriptor is readable.
      */
     virtual CHIP_ERROR ClearCallbackOnPendingRead(SocketWatchToken token) = 0;

     /**
      * Cancel a request for a callback when the associated file descriptor is writable.
      */
     virtual CHIP_ERROR ClearCallbackOnPendingWrite(SocketWatchToken token) = 0;

     /**
      * Stop watching for events on the associated file descriptor.
      *
      * This MUST be called before the file descriptor is closed.
      * It is not necessary to clear callback requests before calling this function.
      */
     virtual CHIP_ERROR StopWatchingSocket(SocketWatchToken * tokenInOut) = 0;

     /**
      * Return a SocketWatchToken that is guaranteed not to be valid. Clients may use this to initialize variables.
      */
     virtual SocketWatchToken InvalidSocketWatchToken() = 0;
 };

 class LayerSocketsLoop;

 /**
  * EventLoopHandlers can be registered with a LayerSocketsLoop instance to enable
  * participation of those handlers in the processing cycle of the event loop. This makes
  * it possible to implement adapters that allow components utilizing a third-party event
  * loop API to participate in the Matter event loop, instead of having to run an entirely
  * separate event loop on another thread.
  *
  * Specifically, the `PrepareEvents` and `HandleEvents` methods of registered event loop
  * handlers will be called from the LayerSocketsLoop methods of the same names.
  *
  * @see LayerSocketsLoop::PrepareEvents
  * @see LayerSocketsLoop::HandleEvents
  */
 class EventLoopHandler : public chip::IntrusiveListNodeBase<>
 {
 public:
     virtual ~EventLoopHandler() {}

     /**
      * Prepares events and returns the next requested wake time.
      */
     virtual Clock::Timestamp PrepareEvents(Clock::Timestamp now) { return Clock::Timestamp::max(); }

     /**
      * Handles / dispatches pending events.
      * Every call to this method will have been preceded by a call to `PrepareEvents`.
      */
     virtual void HandleEvents() = 0;

 private:
     // mState is provided exclusively for use by the LayerSocketsLoop implementation
     // sub-class and can be accessed by it via the LayerSocketsLoop::LoopHandlerState() helper.
     friend class LayerSocketsLoop;
     intptr_t mState = 0;
 };

 class LayerSocketsLoop : public LayerSockets
 {
 public:
     virtual void Signal()          = 0;
     virtual void EventLoopBegins() = 0;
     virtual void PrepareEvents()   = 0;
     virtual void WaitForEvents()   = 0;
     virtual void HandleEvents()    = 0;
     virtual void EventLoopEnds()   = 0;

 #if !CHIP_SYSTEM_CONFIG_USE_DISPATCH
     virtual void AddLoopHandler(EventLoopHandler & handler)    = 0;
     virtual void RemoveLoopHandler(EventLoopHandler & handler) = 0;
 #endif // !CHIP_SYSTEM_CONFIG_USE_DISPATCH

 #if CHIP_SYSTEM_CONFIG_USE_DISPATCH
     virtual void SetDispatchQueue(dispatch_queue_t dispatchQueue) = 0;
     virtual dispatch_queue_t GetDispatchQueue()                   = 0;
 #elif CHIP_SYSTEM_CONFIG_USE_LIBEV
     virtual void SetLibEvLoop(struct ev_loop * aLibEvLoopP) = 0;
     virtual struct ev_loop * GetLibEvLoop()                 = 0;
 #endif // CHIP_SYSTEM_CONFIG_USE_DISPATCH/LIBEV

 protected:
     // Expose EventLoopHandler.mState as a non-const reference to sub-classes
     decltype(EventLoopHandler::mState) & LoopHandlerState(EventLoopHandler & handler) { return handler.mState; }
 };

 #endif // CHIP_SYSTEM_CONFIG_USE_SOCKETS || CHIP_SYSTEM_CONFIG_USE_NETWORK_FRAMEWORK

 } // namespace System
 } // namespace chip
	/*
	*
	* Copyright (c) 2020-2021 Project CHIP Authors
	* Copyright (c) 2016-2017 Nest Labs, Inc.
	*
	* 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.
	*/

	/**
	* @file
	* This file contains declarations of the
	* chip::System::Layer class and its related types, data and
	* functions.
	*/

	#pragma once

	#include <type_traits>
	#include <utility>

	// Include configuration headers
	#include <system/SystemConfig.h>

	#include <lib/core/CHIPCallback.h>

	#include <lib/support/CodeUtils.h>
	#include <lib/support/DLLUtil.h>
	#include <lib/support/LambdaBridge.h>
	#include <system/SystemClock.h>
	#include <system/SystemError.h>
	#include <system/SystemEvent.h>

	#if CHIP_SYSTEM_CONFIG_USE_SOCKETS \|\| CHIP_SYSTEM_CONFIG_USE_NETWORK_FRAMEWORK
	#include <lib/support/IntrusiveList.h>
	#include <system/SocketEvents.h>
	#endif // CHIP_SYSTEM_CONFIG_USE_SOCKETS \|\| CHIP_SYSTEM_USE_NETWORK_FRAMEWORK

	#if CHIP_SYSTEM_CONFIG_USE_DISPATCH
	#include <dispatch/dispatch.h>
	#elif CHIP_SYSTEM_CONFIG_USE_LIBEV
	#include <ev.h>
	#endif // CHIP_SYSTEM_CONFIG_USE_DISPATCH/LIBEV

	namespace chip {
	namespace System {

	class Layer;
	using TimerCompleteCallback = void ()(Layer aLayer, void * appState);

	/**
	* This provides access to timers according to the configured event handling model.
	*
	* The abstract class hierarchy is:
	* - Layer: Core timer methods.
	* - LayerFreeRTOS: Adds methods specific to CHIP_SYSTEM_CONFIG_USING_LWIP and CHIP_SYSTEM_CONFIG_USE_OPEN_THREAD_ENDPOINT.
	* - LayerSockets: Adds I/O event methods specific to CHIP_SYSTEM_CONFIG_USING_SOCKETS.
	* - LayerSocketsLoop: Adds methods for event-loop-based implementations.
	*
	* Threading notes:
	*
	* The SDK is not generally thread safe. System::Layer methods should only be called from
	* a single context, or otherwise externally synchronized. For platforms that use a CHIP
	* event loop thread, timer callbacks are invoked on that thread; for platforms that use
	* a CHIP lock, the lock is held.
	*/
	class DLL_EXPORT Layer
	{
	public:
	Layer() = default;
	virtual ~Layer() = default;

	/**
	* Initialize the Layer.
	*/
	virtual CHIP_ERROR Init() = 0;

	/**
	* Shut down the Layer.
	*
	* Some other layers hold pointers to System::Layer, so care must be taken
	* to ensure that they are not used after calling Shutdown().
	*/
	virtual void Shutdown() = 0;

	/**
	* True if this Layer is initialized. No method on Layer or its abstract descendants, other than this and `Init()`,
	* may be called from general code unless this is true. (Individual Impls may have looser constraints internally.)
	*/
	virtual bool IsInitialized() const = 0;

	/**
	* @brief
	* This method starts a one-shot timer. This method must be called while in the Matter context (from
	* the Matter event loop, or while holding the Matter stack lock).
	*
	* @note
	* Only a single timer is allowed to be started with the same @a aComplete and @a aAppState
	* arguments. If called with @a aComplete and @a aAppState identical to an existing timer,
	* the currently-running timer will first be cancelled.
	*
	* @param[in] aDelay Time before this timer fires.
	* @param[in] aComplete A pointer to the function called when timer expires.
	* @param[in] aAppState A pointer to the application state object used when timer expires.
	*
	* @return CHIP_NO_ERROR On success.
	* @return CHIP_ERROR_NO_MEMORY If a timer cannot be allocated.
	* @return Other Value indicating timer failed to start.
	*/
	virtual CHIP_ERROR StartTimer(Clock::Timeout aDelay, TimerCompleteCallback aComplete, void * aAppState) = 0;

	/**
	* @brief
	* This method extends the timer expiry to the provided aDelay. This method must be called while in the Matter context
	* (from the Matter event loop, or while holding the Matter stack lock).
	* aDelay is not added to the Remaining time of the timer. The finish line is pushed back to aDelay.
	*
	* @note The goal of this method is that the timer remaining time cannot be shrunk and only extended to a new time
	* If the provided new Delay is smaller than the timer's remaining time, the timer is left untouched.
	* In the other case the method acts like StartTimer
	*
	* @param[in] aDelay Time before this timer fires.
	* @param[in] aComplete A pointer to the function called when timer expires.
	* @param[in] aAppState A pointer to the application state object used when timer expires.
	*
	* @return CHIP_NO_ERROR On success.
	* @return CHIP_ERROR_INVALID_ARGUMENT If the provided aDelay value is 0
	* @return CHIP_ERROR_NO_MEMORY If a timer cannot be allocated.
	* @return Other Value indicating timer failed to start.
	*/
	virtual CHIP_ERROR ExtendTimerTo(Clock::Timeout aDelay, TimerCompleteCallback aComplete, void * aAppState) = 0;

	/**
	* @brief
	* This method searches for the timer matching the provided parameters.
	* and returns whether it is still "running" and waiting to trigger or not.
	*
	* @note This is used to verify by how long the ExtendTimer method extends the timer, as it may ignore an extension request
	* if it is shorter than the current timer's remaining time.
	*
	* @param[in] onComplete A pointer to the function called when timer expires.
	* @param[in] appState A pointer to the application state object used when timer expires.
	*
	* @return True if there is a current timer set to call, at some point in the future, the provided onComplete callback
	* with the corresponding appState context. False otherwise.
	*/
	virtual bool IsTimerActive(TimerCompleteCallback onComplete, void * appState) = 0;

	/**
	* @brief
	* This method searches for the timer matching the provided parameters
	* and returns the remaining time left before it expires.
	* @param[in] onComplete A pointer to the function called when timer expires.
	* @param[in] appState A pointer to the application state object used when timer expires.
	*
	* @return The remaining time left before the timer expires.
	*/
	virtual Clock::Timeout GetRemainingTime(TimerCompleteCallback onComplete, void * appState) = 0;

	/**
	* @brief This method cancels a one-shot timer, started earlier through @p StartTimer(). This method must
	* be called while in the Matter context (from the Matter event loop, or while holding the Matter
	* stack lock).
	*
	* @note
	* The cancellation could fail silently if the timer specified by the combination of the callback
	* function and application state object couldn't be found.
	*
	* @param[in] aOnComplete A pointer to the callback function used in calling @p StartTimer().
	* @param[in] aAppState A pointer to the application state object used in calling @p StartTimer().
	*
	*/
	virtual void CancelTimer(TimerCompleteCallback aOnComplete, void * aAppState) = 0;

	/**
	* @brief
	* Schedules a `TimerCompleteCallback` to be run as soon as possible in the Matter context.
	*
	* WARNING: This must only be called when already in the Matter context (from the Matter event loop, or
	* while holding the Matter stack lock). The `PlatformMgr::ScheduleWork()` equivalent method
	* is safe to call outside Matter context.
	*
	* @param[in] aComplete A pointer to a callback function to be called when this timer fires.
	* @param[in] aAppState A pointer to an application state object to be passed to the callback function as argument.
	*
	* @retval CHIP_ERROR_INCORRECT_STATE If the System::Layer has not been initialized.
	* @retval CHIP_ERROR_NO_MEMORY If the SystemLayer cannot allocate a new timer.
	* @retval CHIP_NO_ERROR On success.
	*/
	virtual CHIP_ERROR ScheduleWork(TimerCompleteCallback aComplete, void * aAppState) = 0;

	/**
	* @brief
	* Schedules a lambda object to be run as soon as possible in the Matter context.
	*
	* This is safe to call from any context and will guarantee execution in Matter context.
	* Note that the Lambda's capture have to fit within `CHIP_CONFIG_LAMBDA_EVENT_SIZE` bytes.
	*
	* @param[in] lambda The Lambda to execute in Matter context.
	*
	* @retval CHIP_NO_ERROR On success.
	* @retval other Platform-specific errors generated indicating the reason for failure.
	*/
	template <typename Lambda>
	CHIP_ERROR ScheduleLambda(const Lambda & lambda)
	{
	static_assert(std::is_invocable_v<Lambda>, "lambda argument must be an invocable with no arguments");
	LambdaBridge bridge;
	bridge.Initialize(lambda);
	return ScheduleLambdaBridge(std::move(bridge));
	}

	private:
	CHIP_ERROR ScheduleLambdaBridge(LambdaBridge && bridge);

	// Not copyable
	Layer(const Layer &) = delete;
	Layer & operator=(const Layer &) = delete;
	};

	#if CHIP_SYSTEM_CONFIG_USE_LWIP \|\| CHIP_SYSTEM_CONFIG_USE_OPEN_THREAD_ENDPOINT

	class LayerFreeRTOS : public Layer
	{
	};

	#endif // CHIP_SYSTEM_CONFIG_USE_LWIP

	#if CHIP_SYSTEM_CONFIG_USE_SOCKETS \|\| CHIP_SYSTEM_CONFIG_USE_NETWORK_FRAMEWORK

	class LayerSockets : public Layer
	{
	public:
	/**
	* Initialize watching for events on a file descriptor.
	*
	* Returns an opaque token through @a tokenOut that must be passed to subsequent operations for this file descriptor.
	* Multiple calls to start watching the same file descriptor will return the same token.
	* StopWatchingSocket() must be called before closing the file descriptor.
	*/
	virtual CHIP_ERROR StartWatchingSocket(int fd, SocketWatchToken * tokenOut) = 0;

	/**
	* Register a callback function.
	*
	* The callback will be invoked (with the CHIP stack lock held) when requested event(s) are ready.
	*/
	virtual CHIP_ERROR SetCallback(SocketWatchToken token, SocketWatchCallback callback, intptr_t data) = 0;

	/**
	* Request a callback when the associated file descriptor is readable.
	*/
	virtual CHIP_ERROR RequestCallbackOnPendingRead(SocketWatchToken token) = 0;

	/**
	* Request a callback when the associated file descriptor is writable.
	*/
	virtual CHIP_ERROR RequestCallbackOnPendingWrite(SocketWatchToken token) = 0;

	/**
	* Cancel a request for a callback when the associated file descriptor is readable.
	*/
	virtual CHIP_ERROR ClearCallbackOnPendingRead(SocketWatchToken token) = 0;

	/**
	* Cancel a request for a callback when the associated file descriptor is writable.
	*/
	virtual CHIP_ERROR ClearCallbackOnPendingWrite(SocketWatchToken token) = 0;

	/**
	* Stop watching for events on the associated file descriptor.
	*
	* This MUST be called before the file descriptor is closed.
	* It is not necessary to clear callback requests before calling this function.
	*/
	virtual CHIP_ERROR StopWatchingSocket(SocketWatchToken * tokenInOut) = 0;

	/**
	* Return a SocketWatchToken that is guaranteed not to be valid. Clients may use this to initialize variables.
	*/
	virtual SocketWatchToken InvalidSocketWatchToken() = 0;
	};

	class LayerSocketsLoop;

	/**
	* EventLoopHandlers can be registered with a LayerSocketsLoop instance to enable
	* participation of those handlers in the processing cycle of the event loop. This makes
	* it possible to implement adapters that allow components utilizing a third-party event
	* loop API to participate in the Matter event loop, instead of having to run an entirely
	* separate event loop on another thread.
	*
	* Specifically, the `PrepareEvents` and `HandleEvents` methods of registered event loop
	* handlers will be called from the LayerSocketsLoop methods of the same names.
	*
	* @see LayerSocketsLoop::PrepareEvents
	* @see LayerSocketsLoop::HandleEvents
	*/
	class EventLoopHandler : public chip::IntrusiveListNodeBase<>
	{
	public:
	virtual ~EventLoopHandler() {}

	/**
	* Prepares events and returns the next requested wake time.
	*/
	virtual Clock::Timestamp PrepareEvents(Clock::Timestamp now) { return Clock::Timestamp::max(); }

	/**
	* Handles / dispatches pending events.
	* Every call to this method will have been preceded by a call to `PrepareEvents`.
	*/
	virtual void HandleEvents() = 0;

	private:
	// mState is provided exclusively for use by the LayerSocketsLoop implementation
	// sub-class and can be accessed by it via the LayerSocketsLoop::LoopHandlerState() helper.
	friend class LayerSocketsLoop;
	intptr_t mState = 0;
	};

	class LayerSocketsLoop : public LayerSockets
	{
	public:
	virtual void Signal() = 0;
	virtual void EventLoopBegins() = 0;
	virtual void PrepareEvents() = 0;
	virtual void WaitForEvents() = 0;
	virtual void HandleEvents() = 0;
	virtual void EventLoopEnds() = 0;

	#if !CHIP_SYSTEM_CONFIG_USE_DISPATCH
	virtual void AddLoopHandler(EventLoopHandler & handler) = 0;
	virtual void RemoveLoopHandler(EventLoopHandler & handler) = 0;
	#endif // !CHIP_SYSTEM_CONFIG_USE_DISPATCH

	#if CHIP_SYSTEM_CONFIG_USE_DISPATCH
	virtual void SetDispatchQueue(dispatch_queue_t dispatchQueue) = 0;
	virtual dispatch_queue_t GetDispatchQueue() = 0;
	#elif CHIP_SYSTEM_CONFIG_USE_LIBEV
	virtual void SetLibEvLoop(struct ev_loop * aLibEvLoopP) = 0;
	virtual struct ev_loop * GetLibEvLoop() = 0;
	#endif // CHIP_SYSTEM_CONFIG_USE_DISPATCH/LIBEV

	protected:
	// Expose EventLoopHandler.mState as a non-const reference to sub-classes
	decltype(EventLoopHandler::mState) & LoopHandlerState(EventLoopHandler & handler) { return handler.mState; }
	};

	#endif // CHIP_SYSTEM_CONFIG_USE_SOCKETS \|\| CHIP_SYSTEM_CONFIG_USE_NETWORK_FRAMEWORK

	} // namespace System
	} // namespace chip