[libcamera-devel] [PATCH v2 05/11] libcamera: Add signal/slot communication mechanism
Laurent Pinchart
laurent.pinchart at ideasonboard.com
Tue Jan 8 00:11:45 CET 2019
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>
Reviewed-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
---
Changes since v1:
- Improve documentation
- Add support for static slots
---
Documentation/Doxyfile.in | 4 +-
include/libcamera/meson.build | 1 +
include/libcamera/signal.h | 154 ++++++++++++++++++++++++++++++++++
src/libcamera/meson.build | 1 +
src/libcamera/signal.cpp | 84 +++++++++++++++++++
5 files changed, 243 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..aac20839c837 100644
--- a/Documentation/Doxyfile.in
+++ b/Documentation/Doxyfile.in
@@ -860,7 +860,9 @@ 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::SlotMember \
+ libcamera::SlotStatic
# 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..458db1ac0060
--- /dev/null
+++ b/include/libcamera/signal.h
@@ -0,0 +1,154 @@
+/* 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 SlotMember : public SlotBase<Args...>
+{
+public:
+ SlotMember(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 SlotStatic : public SlotBase<Args...>
+{
+public:
+ SlotStatic(void(*func)(Args...))
+ : SlotBase<Args...>(nullptr), func_(func) { }
+
+ void invoke(Args... args) { (*func_)(args...); }
+
+private:
+ friend class Signal<Args...>;
+ void(*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 SlotMember<T, Args...>(object, func));
+ }
+
+ void connect(void(*func)(Args...))
+ {
+ slots_.push_back(new SlotStatic<Args...>(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 the obj_ pointer matches the object types must
+ * match, so we can safely case to SlotMember<T, Args>.
+ */
+ if (slot->obj_ == object &&
+ reinterpret_cast<SlotMember<T, Args...> *>(slot)->func_ == func) {
+ iter = slots_.erase(iter);
+ delete slot;
+ } else {
+ ++iter;
+ }
+ }
+ }
+
+ void disconnect(void(*func)(Args...))
+ {
+ for (auto iter = slots_.begin(); iter != slots_.end(); ) {
+ SlotBase<Args...> *slot = *iter;
+ if (slot->obj_ == nullptr &&
+ reinterpret_cast<SlotStatic<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..0fd3bb2a34a1
--- /dev/null
+++ b/src/libcamera/signal.cpp
@@ -0,0 +1,84 @@
+/* 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.
+ *
+ * Signals model events that can be observed from objects unrelated to the event
+ * source. Slots are functions that are called in response to a signal. Signals
+ * can be connected to and disconnected from slots dynamically at runtime. When
+ * a signal is emitted, all connected slots are called sequentially in the order
+ * they have been connected.
+ *
+ * Signals are defined with zero, one or more typed parameters. They are emitted
+ * with a value for each of the parameters, and those values are passed to the
+ * connected slots.
+ *
+ * Slots are normal static or class member functions. In order to be connected
+ * to a signal, their signature must match the signal type (taking the same
+ * arguments as the signal and returning void).
+ *
+ * Connecting a signal to a slot results in the slot being called with the
+ * arguments passed to the emit() function when the signal is emitted. Multiple
+ * slots can be connected to the same signal, and multiple signals can connected
+ * to the same slot. Duplicate connections between a signal and a slot are
+ * allowed and result in the slot being called multiple times for the same
+ * signal emission.
+ */
+
+/**
+ * \fn Signal::connect(T *object, void(T::*func)(Args...))
+ * \brief Connect the signal to a member function slot
+ * \param object The slot object pointer
+ * \param func The slot member function
+ */
+
+/**
+ * \fn Signal::connect(void(*func)(Args...))
+ * \brief Connect the signal to a static function slot
+ * \param func The slot static function
+ */
+
+/**
+ * \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 the \a object slot member function \a func
+ */
+
+/**
+ * \fn Signal::disconnect(void(*func)(Args...))
+ * \brief Disconnect the signal from the slot static function \a func
+ */
+
+/**
+ * \fn Signal::emit(Args... args)
+ * \brief Emit the signal and call all connected slots
+ *
+ * Emitting a signal calls all connected slots synchronously and sequentially in
+ * the order the slots have been connected. The arguments passed to the emit()
+ * function are passed to the slot functions unchanged. If a slot modifies one
+ * of the arguments (when passed by pointer or reference), the modification is
+ * thus visible to all subsequently called slots.
+ */
+
+} /* namespace libcamera */
--
Regards,
Laurent Pinchart
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