[libcamera-devel] [PATCH 05/11] libcamera: Add signal/slot communication mechanism

[Niklas Söderlund]

Hi Laurent,

Thanks for your patch.

On 2019-01-06 04:33:22 +0200, Laurent Pinchart wrote:
> Introduce a Signal class that allows connecting event sources (signals)
> to event listeners (slots) without adding any boilerplate code usually
> associated with the observer or listener design patterns.
> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

It takes some time to wrap your head around this one, but I like it.

Reviewed-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>

> ---
>  Documentation/Doxyfile.in     |   3 +-
>  include/libcamera/meson.build |   1 +
>  include/libcamera/signal.h    | 117 ++++++++++++++++++++++++++++++++++
>  src/libcamera/meson.build     |   1 +
>  src/libcamera/signal.cpp      |  44 +++++++++++++
>  5 files changed, 165 insertions(+), 1 deletion(-)
>  create mode 100644 include/libcamera/signal.h
>  create mode 100644 src/libcamera/signal.cpp
> 
> diff --git a/Documentation/Doxyfile.in b/Documentation/Doxyfile.in
> index b1a70d36eee5..558a1ce04377 100644
> --- a/Documentation/Doxyfile.in
> +++ b/Documentation/Doxyfile.in
> @@ -860,7 +860,8 @@ EXCLUDE_PATTERNS       =
>  # Note that the wildcards are matched against the file with absolute path, so to
>  # exclude all test directories use the pattern */test/*
>  
> -EXCLUDE_SYMBOLS        =
> +EXCLUDE_SYMBOLS        = libcamera::SlotBase \
> +                         libcamera::Slot
>  
>  # The EXAMPLE_PATH tag can be used to specify one or more files or directories
>  # that contain example code fragments that are included (see the \include
> diff --git a/include/libcamera/meson.build b/include/libcamera/meson.build
> index 3e04557d66b1..6f87689ea528 100644
> --- a/include/libcamera/meson.build
> +++ b/include/libcamera/meson.build
> @@ -2,6 +2,7 @@ libcamera_api = files([
>      'camera.h',
>      'camera_manager.h',
>      'libcamera.h',
> +    'signal.h',
>  ])
>  
>  install_headers(libcamera_api,
> diff --git a/include/libcamera/signal.h b/include/libcamera/signal.h
> new file mode 100644
> index 000000000000..fceb852158ec
> --- /dev/null
> +++ b/include/libcamera/signal.h
> @@ -0,0 +1,117 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2019, Google Inc.
> + *
> + * signal.h - Signal & slot implementation
> + */
> +#ifndef __LIBCAMERA_SIGNAL_H__
> +#define __LIBCAMERA_SIGNAL_H__
> +
> +#include <list>
> +#include <vector>
> +
> +namespace libcamera {
> +
> +template<typename... Args>
> +class Signal;
> +
> +template<typename... Args>
> +class SlotBase
> +{
> +public:
> +	SlotBase(void *obj)
> +		: obj_(obj) { }
> +	virtual ~SlotBase() { }
> +
> +	virtual void invoke(Args... args) = 0;
> +
> +protected:
> +	friend class Signal<Args...>;
> +	void *obj_;
> +};
> +
> +template<typename T, typename... Args>
> +class Slot : public SlotBase<Args...>
> +{
> +public:
> +	Slot(T *obj, void(T::*func)(Args...))
> +		: SlotBase<Args...>(obj), func_(func) { }
> +
> +	void invoke(Args... args) { (reinterpret_cast<T *>(this->obj_)->*func_)(args...); }
> +
> +private:
> +	friend class Signal<Args...>;
> +	void(T::*func_)(Args...);
> +};
> +
> +template<typename... Args>
> +class Signal
> +{
> +public:
> +	Signal() { }
> +	~Signal()
> +	{
> +		for (SlotBase<Args...> *slot : slots_)
> +			delete slot;
> +	}
> +
> +	template<typename T>
> +	void connect(T *object, void(T::*func)(Args...))
> +	{
> +		slots_.push_back(new Slot<T, Args...>(object, func));
> +	}
> +
> +	void disconnect()
> +	{
> +		for (SlotBase<Args...> *slot : slots_)
> +			delete slot;
> +		slots_.clear();
> +	}
> +
> +	template<typename T>
> +	void disconnect(T *object)
> +	{
> +		for (auto iter = slots_.begin(); iter != slots_.end(); ) {
> +			SlotBase<Args...> *slot = *iter;
> +			if (slot->obj_ == object) {
> +				iter = slots_.erase(iter);
> +				delete slot;
> +			} else {
> +				++iter;
> +			}
> +		}
> +	}
> +
> +	template<typename T>
> +	void disconnect(T *object, void(T::*func)(Args...))
> +	{
> +		for (auto iter = slots_.begin(); iter != slots_.end(); ) {
> +			SlotBase<Args...> *slot = *iter;
> +			if (slot->obj_ == object &&
> +			    reinterpret_cast<Slot<T, Args...> *>(slot)->func_ == func) {
> +				iter = slots_.erase(iter);
> +				delete slot;
> +			} else {
> +				++iter;
> +			}
> +		}
> +	}
> +
> +	void emit(Args... args)
> +	{
> +		/*
> +		 * Make a copy of the slots list as the slot could call the
> +		 * disconnect operation, invalidating the iterator.
> +		 */
> +		std::vector<SlotBase<Args...> *> slots{ slots_.begin(), slots_.end() };
> +		for (SlotBase<Args...> *slot : slots)
> +			slot->invoke(args...);
> +	}
> +
> +private:
> +	std::list<SlotBase<Args...> *> slots_;
> +};
> +
> +} /* namespace libcamera */
> +
> +#endif /* __LIBCAMERA_SIGNAL_H__ */
> diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
> index 78562299fc42..3ec86e75b57e 100644
> --- a/src/libcamera/meson.build
> +++ b/src/libcamera/meson.build
> @@ -6,6 +6,7 @@ libcamera_sources = files([
>      'media_device.cpp',
>      'media_object.cpp',
>      'pipeline_handler.cpp',
> +    'signal.cpp',
>  ])
>  
>  libcamera_headers = files([
> diff --git a/src/libcamera/signal.cpp b/src/libcamera/signal.cpp
> new file mode 100644
> index 000000000000..8b5a6c285c55
> --- /dev/null
> +++ b/src/libcamera/signal.cpp
> @@ -0,0 +1,44 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2019, Google Inc.
> + *
> + * signal.cpp - Signal & slot implementation
> + */
> +
> +namespace libcamera {
> +
> +/**
> + * \class Signal
> + * \brief Generic signal and slot communication mechanism
> + *
> + * Signals and slots are a language construct aimed at communication between
> + * objects through the observer pattern without the need for boilerplate code.
> + * See http://doc.qt.io/qt-5/signalsandslots.html for more information.
> + */
> +
> +/**
> + * \fn Signal::connect()
> + * \brief Connect the signal to a slot
> + */
> +
> +/**
> + * \fn Signal::disconnect()
> + * \brief Disconnect the signal from all slots
> + */
> +
> +/**
> + * \fn Signal::disconnect(T *object)
> + * \brief Disconnect the signal from all slots of the \a object
> + */
> +
> +/**
> + * \fn Signal::disconnect(T *object, void(T::*func)(Args...))
> + * \brief Disconnect the signal from a slot of the \a object
> + */
> +
> +/**
> + * \fn Signal::emit()
> + * \brief Emit the signal and call all connected slots
> + */
> +
> +} /* namespace libcamera */
> -- 
> Regards,
> 
> Laurent Pinchart
> 
> _______________________________________________
> libcamera-devel mailing list
> libcamera-devel at lists.libcamera.org
> https://lists.libcamera.org/listinfo/libcamera-devel

-- 
Regards,
Niklas Söderlund