Resource Guard

Use the fexibility of lambda expressions to prevent resource leak.

Motivation

To avoid resource leak when porting legacy code most time we have to create several micro classes using RAII idom. To prevent the proliferation of these micro classes we could optionally use lambda expressions.

Example

// ...
#include <ResourceGuard.h>

class App
{
public:
	App() {
		ResourceGuardChain algorithms;
	
		if(init_device() != OK) {
			throw std::runtime_error("init_device() failed\n");
		}

		algorithms.add(new ResourceGuard([](){
			close_device();
		}));

		if(open_window() != OK) {
			throw std::runtime_error("open_window() failed\n");
		}

		algorithms.add(new ResourceGuard([](){
			close_window();
		}));

		if(create_opengl_context() != OK) {
			throw std::runtime_error("create_opengl_context() failed\n");
		}

		algorithms.freeAll();
	}
	
	~App() {
		destroy_opengl_context();
		close_window();
		close_device();
	}
};

int main() {
	try {
		App app;
		std::cout << "app successful created\n";
	} catch (std::exception& e) {
		std::cerr << "exception occurs: " << e.what() << '\n';
		return -1;
	}

	return 0;
}

one possible output is:

trying init device... device initialized
try opening window... window opened
trying create a opengl context... context created
app successful created

But if something went wrong and the context couldn't be create, we got:

trying init device... device initialized
try opening window... window opened
trying create a opengl context... can't create context
close_window()
close_device()
exception occurs: create_opengl_context() failed

Note the destructors were called in the reverse order.

For simple tasks, one could use a single resource guard:

App() {
	if(init_device() != OK) {
		throw std::runtime_error("init_device() failed\n");
	}

	ResourceGuard device_guard([](){
		close_device();
	});

	open_window_with_opengl_context();

	device_guard.free();
}

Macro version

When working with c++11 and c++14 you should use the macro version of the library.

App() {
	ResourceGuardChain algorithms;

	if(init_device() != OK) {
		throw std::runtime_error("init_device() failed\n");
	}

	ADD_RESOURCE_GUARD(algorithms, [](){
		close_device();
	});
	...
	algorithms.freeAll();
}

or single resource guard:

App() {
	if(init_device() != OK) {
		throw std::runtime_error("init_device() failed\n");
	}
	
	SINGLE_RESOURCE_GUARD(device_guard, ([](){
		close_device();
	});

	open_window_with_opengl_context();
	
	device_guard.free();
}

Build

Resource Guard is a header only file. Just download ResourceGuard.h and place it in a folder your compile can find.

Compatibility

• Macro version should works with all c++11 and latter compliance compilers.
• Class version should works with all c++17 and latter compliance compilers. One exception is vs2015 because it doesn't fully support all c++17 features.