BadTimer.cpp

// clang++ BadTimer.cpp -fPIC -shared -O3 -std=c++11 -o BadTimer.dylib
#include <chrono>

class BadTimer {
	private:
		std::chrono::high_resolution_clock::time_point startTime;
		std::chrono::high_resolution_clock::time_point endTime;
		std::chrono::duration<double> timeSpan;
	public:
		BadTimer( void );
		double getElapsedTime( void );
};

BadTimer::BadTimer( void ) {
	startTime = std::chrono::high_resolution_clock::now( );
}

double BadTimer::getElapsedTime( void ) {
	endTime = std::chrono::high_resolution_clock::now( );
	timeSpan = std::chrono::duration_cast<std::chrono::duration<double>>(endTime - startTime);
	return timeSpan.count( );
}

extern "C" {
	void* startTimer( void ) {
		return new BadTimer;
	}

	double getDuration( BadTimer *badTimer ) {
		return badTimer->getElapsedTime( );
	}

	void freeTimer( BadTimer *badTimer ) {
		delete badTimer;
	}
}

BadTimer.lua

ffi = require"ffi"
ffi.cdef[[
void* startTimer( void );
double getDuration( void* );
void freeTimer( void* );
]]
badTimer = ffi.load"./BadTimer.dylib"

bad = badTimer.startTimer( )
print(("%g us"):format(badTimer.getDuration(bad)*1000000))
print(("%g us"):format(badTimer.getDuration(bad)*1000000))
print(("%g us"):format(badTimer.getDuration(bad)*1000000))
badTimer.freeTimer(bad)