Adserver Plugins

CMakeLists.txt

cmake_minimum_required(VERSION 3.0)
project(plugins)

########
add_library(mylib
	mylib.cpp
)
target_compile_options(mylib PRIVATE -fPIC)

########
add_library(plugin SHARED
	plugin.cpp
)
target_link_libraries(plugin
	mylib
)
target_compile_options(plugin PRIVATE -fvisibility=hidden)

########
add_executable(a.out
	main.cpp
)
target_link_libraries(a.out
	mylib
)

main.cpp

#include "mylib.h"
#include "plugin.h"

#include <iostream>
#include <dlfcn.h>

class MyClassMain final : public MyClass
{
public:
	MyClassMain() { ++libInc; }

	void set(int val) final { MyClass::set(val + 10); }
};

int
main()
{
	void* plugin = dlopen("./libplugin.so", RTLD_NOW | RTLD_LOCAL);
	if (plugin == nullptr)
	{
		std::cout << "Couldn't load plugin\n";
		return -1;
	}

	makeInstanceFunc* makeInstanceF = (makeInstanceFunc*)dlsym(plugin, "_Z12makeInstancev");
	if (makeInstanceF == nullptr)
	{
		std::cout << "Couldn't load makeInstance\n";
		return -1;
	}
	pluginPrintInfoFunc* pluginPrintInfoF = (pluginPrintInfoFunc*)dlsym(plugin, "_Z15pluginPrintInfov");
	if (pluginPrintInfoF == nullptr)
	{
		std::cout << "Couldn't load pluginPrintInfo\n";
		return -1;
	}

	std::cout << "Main::libInc: " << libInc << '\n';
	pluginPrintInfoF();

	{
		MyClassMain c;
		c.set(10);
		std::cout << "Main class, val = " << c.get() << '\n';

		std::cout << "Main::libInc: " << libInc << '\n';
		pluginPrintInfoF();
	}
	for (int i = 0; i < 2; ++i)
	{
		MyClass* c = makeInstanceF();
		c->set(10);
		std::cout << "Plugin class, val = " << c->get() << '\n';

		std::cout << "Main::libInc: " << libInc << '\n';
		pluginPrintInfoF();

		delete c;
	}

	dlclose(plugin);
	return 0;
}

mylib.cpp

#include "mylib.h"

MyClass::MyClass() : myVal(0) {}

void MyClass::set(int val) { myVal = val; }

int libInc = 0;

mylib.h

#pragma once

class MyClass
{
public:
	MyClass();
	virtual ~MyClass() = default;

	virtual void set(int val);

	int get() const { return myVal; }

private:
	int myVal;
};

extern int libInc;

plugin.cpp

#include "plugin.h"
#include "mylib.h"

#include <iostream>

namespace
{
class MyClassPlugin final : public MyClass
{
public:
	MyClassPlugin() { ++libInc; }

private:
	void set(int val) final { MyClass::set(val * 10); }
};
}

MyClass* makeInstance()
{
	return new MyClassPlugin();
}

void pluginPrintInfo()
{
	std::cout << "Plugin::libInc: " << libInc << '\n';
}

plugin.h

#pragma once

#include "mylib.h"

#define PLUGIN_API __attribute__((__visibility__("default")))

PLUGIN_API MyClass* makeInstance();

using makeInstanceFunc = decltype(makeInstance);

PLUGIN_API void pluginPrintInfo();

using pluginPrintInfoFunc = decltype(pluginPrintInfo);