libcamera: signal: Split Slot implementation to reusable classes

Move the Slot* classes to bound_method.{h,cpp} and rename them to
Bound*Method*. They will be reused to implement asynchronous method
invocation similar to cross-thread signal delivery.

This is only a move and rename, no functional changes are included.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

include/libcamera/bound_method.h

@@ -0,0 +1,131 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * bound_method.h - Method bind and invocation
+ */
+#ifndef __LIBCAMERA_BOUND_METHOD_H__
+#define __LIBCAMERA_BOUND_METHOD_H__
+
+#include <tuple>
+#include <type_traits>
+
+namespace libcamera {
+
+class Object;
+template<typename... Args>
+class Signal;
+class SignalBase;
+
+class BoundMethodBase
+{
+public:
+	BoundMethodBase(void *obj, Object *object)
+		: obj_(obj), object_(object) {}
+	virtual ~BoundMethodBase() {}
+
+	template<typename T, typename std::enable_if<!std::is_same<Object, T>::value>::type * = nullptr>
+	bool match(T *obj) { return obj == obj_; }
+	bool match(Object *object) { return object == object_; }
+
+	void disconnect(SignalBase *signal);
+
+	void activatePack(void *pack);
+	virtual void invokePack(void *pack) = 0;
+
+protected:
+	void *obj_;
+	Object *object_;
+};
+
+template<typename... Args>
+class BoundMethodArgs : public BoundMethodBase
+{
+private:
+#ifndef __DOXYGEN__
+	/*
+	 * This is a cheap partial implementation of std::integer_sequence<>
+	 * from C++14.
+	 */
+	template<int...>
+	struct sequence {
+	};
+
+	template<int N, int... S>
+	struct generator : generator<N-1, N-1, S...> {
+	};
+
+	template<int... S>
+	struct generator<0, S...> {
+		typedef sequence<S...> type;
+	};
+#endif
+
+	using PackType = std::tuple<typename std::remove_reference<Args>::type...>;
+
+	template<int... S>
+	void invokePack(void *pack, sequence<S...>)
+	{
+		PackType *args = static_cast<PackType *>(pack);
+		invoke(std::get<S>(*args)...);
+		delete args;
+	}
+
+public:
+	BoundMethodArgs(void *obj, Object *object)
+		: BoundMethodBase(obj, object) {}
+
+	void invokePack(void *pack) override
+	{
+		invokePack(pack, typename generator<sizeof...(Args)>::type());
+	}
+
+	virtual void activate(Args... args) = 0;
+	virtual void invoke(Args... args) = 0;
+};
+
+template<typename T, typename... Args>
+class BoundMemberMethod : public BoundMethodArgs<Args...>
+{
+public:
+	using PackType = std::tuple<typename std::remove_reference<Args>::type...>;
+
+	BoundMemberMethod(T *obj, Object *object, void (T::*func)(Args...))
+		: BoundMethodArgs<Args...>(obj, object), func_(func) {}
+
+	void activate(Args... args)
+	{
+		if (this->object_)
+			BoundMethodBase::activatePack(new PackType{ args... });
+		else
+			(static_cast<T *>(this->obj_)->*func_)(args...);
+	}
+
+	void invoke(Args... args)
+	{
+		(static_cast<T *>(this->obj_)->*func_)(args...);
+	}
+
+private:
+	friend class Signal<Args...>;
+	void (T::*func_)(Args...);
+};
+
+template<typename... Args>
+class BoundStaticMethod : public BoundMethodArgs<Args...>
+{
+public:
+	BoundStaticMethod(void (*func)(Args...))
+		: BoundMethodArgs<Args...>(nullptr, nullptr), func_(func) {}
+
+	void activate(Args... args) { (*func_)(args...); }
+	void invoke(Args... args) {}
+
+private:
+	friend class Signal<Args...>;
+	void (*func_)(Args...);
+};
+
+}; /* namespace libcamera */
+
+#endif /* __LIBCAMERA_BOUND_METHOD_H__ */