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

[Laurent Pinchart]

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
 
 # 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