[libcamera-devel] [PATCH 05/11] libcamera: Add signal/slot communication mechanism
Laurent Pinchart
laurent.pinchart at ideasonboard.com
Mon Jan 7 17:49:59 CET 2019
Hi Jacopo,
On Monday, 7 January 2019 16:46:54 EET Jacopo Mondi wrote:
> On Sun, Jan 06, 2019 at 04:33:22AM +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>
> > ---
> >
> > 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
>
> Why exclude from generated documentation?
Because they're internal to the Signal implementation. I have to define those
classes in the header file as they're templates, but they're not part of any
API. I thus don't think we need API documentation (especially given how
trivial each function is).
> > # 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;
> > +
>
> A few questions here:
>
> > +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_;
> > +};
>
> 1) what is the purpose of the non-invokable SlotBase if only Slot is then
> actually used? Do you expect to have more derived classes? I assume
> so, how would you instanciate one or the other from a Signal instance?
The reason I need SlotBase is to implement the function of the Signal class
that don't have a typename T template argument. For instance I can't do
~Signal()
{
for (Slot<T, Args...> *slot : slots_)
delete slot;
}
as there's no typename T here.
> > +
> > +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...);
>
> As invoke is public, do you need to declare Signal as friend class?
The most disconnect(T *object, void(T::*func)(Args...)) variant needs to
access func_.
> > +};
> >
> > +
> > +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...);
> > + }
>
> Why are all these methods inline when this practice has been
> discouraged for all other components of the library?
Because templates have to be inlined, as they're compiled when they are
specialized with type parameters. If there's a way to move these functions to
the .cpp file, please let me know :-)
> > +
> > +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
More information about the libcamera-devel
mailing list