Accessing shared memory from different core

Accessing shared memory from different core Result

pi@raspberrypi:~/multi/build $ ./main 
total num = 10000000
cntx0y0 = 47 (0.0000047000)
cntx1y1 = 9893013 (0.9893013000)
cntx1y0 = 4 (0.0000004000)
cntx0y1 = 106935 (0.0106935000)

CMakeLists.txt

cmake_minimum_required(VERSION 3.0)

set(ProjectName "main")
project(${ProjectName})

# Compile option
if(NOT MSVC)
	set(CMAKE_C_FLAGS "-Wall")
	set(CMAKE_C_FLAGS_RELEASE "-O2 -DNDEBUG")
	set(CMAKE_C_FLAGS_DEBUG "-g3 -O0")
	set(CMAKE_CXX_FLAGS "${CMAKE_C_FLAGS} -std=c++11 -lstdc++")
	set(CMAKE_CXX_FLAGS_RELEASE ${CMAKE_C_FLAGS_RELEASE})
	set(CMAKE_CXX_FLAGS_DEBUG ${CMAKE_C_FLAGS_DEBUG})
	if (NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
		message(STATUS "No build type selected, default to Release")
		set(CMAKE_BUILD_TYPE "Release" CACHE STRING "Build type (default Debug)" FORCE)
	endif()
endif()

find_package(OpenMP REQUIRED)
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OpenMP_C_FLAGS}")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")

# Create executable file
add_executable(${ProjectName} Main.cpp)
target_link_libraries(${ProjectName} pthread)

Main.cpp

#if 1
#include <stdio.h>
#include <unistd.h>

int x;
int y;
int readx;
int ready;

int main()
{
	const long LOOP_NUM_MAX = 10000000;
	long cntx0y0 = 0;
	long cntx1y1 = 0;
	long cntx1y0 = 0;
	long cntx0y1 = 0;
	
	long cnt = 1;
	for (cnt = 1; cnt < LOOP_NUM_MAX; cnt++) {
		x = 0;
		y = 0;
		readx = 0;
		ready = 0;
		#pragma omp parallel
		#pragma omp sections
		{
			#pragma omp section
			{
				// usleep(0);
				x = 1;
				y = 1;
			}
			#pragma omp section
			{
				// usleep(0);
				ready = y;
				readx = x;
			}
		}
		if (readx == 0 && ready == 0) cntx0y0++;
		if (readx == 1 && ready == 1) cntx1y1++;
		if (readx == 1 && ready == 0) cntx1y0++;
		if (readx == 0 && ready == 1) cntx0y1++;	// should not happen

		// if (cntx0y1 > 0) break;
	}
	printf("total num = %ld\n", cnt);
	printf("cntx0y0 = %ld (%.010lf)\n", cntx0y0, cntx0y0 / (double)cnt);
	printf("cntx1y1 = %ld (%.010lf)\n", cntx1y1, cntx1y1 / (double)cnt);
	printf("cntx1y0 = %ld (%.010lf)\n", cntx1y0, cntx1y0 / (double)cnt);
	printf("cntx0y1 = %ld (%.010lf)\n", cntx0y1, cntx0y1 / (double)cnt);
	
	return 0;
}
#endif


#if 0
#include <stdio.h>
#include <unistd.h>
#include <thread>

int x;
int y;
int readx;
int ready;

void func0()
{
	usleep(1);
	x = 1;
	y = 1;

}

void func1()
{
	usleep(1);
	ready = y;
	readx = x;
}

int main()
{
	const int LOOP_NUM_MAX = 10000;
	int cntx0y0 = 0;
	int cntx1y1 = 0;
	int cntx1y0 = 0;
	int cntx0y1 = 0;
	int cnt = 1;
	for (cnt = 1; cnt < LOOP_NUM_MAX; cnt++) {
		x = 0;
		y = 0;
		readx = 0;
		ready = 0;
		std::thread th0(func0);
		std::thread th1(func1);
		th0.join();
		th1.join();
		if (readx == 0 && ready == 0) cntx0y0++;
		if (readx == 1 && ready == 1) cntx1y1++;
		if (readx == 1 && ready == 0) cntx1y0++;
		if (readx == 0 && ready == 1) cntx0y1++;	// should not happen
		if (cntx0y1 > 0) break;
	}

	printf("cntx0y0 = %d (%.010lf)\n", cntx0y0, cntx0y0 / (double)cnt);
	printf("cntx1y1 = %d (%.010lf)\n", cntx1y1, cntx1y1 / (double)cnt);
	printf("cntx1y0 = %d (%.010lf)\n", cntx1y0, cntx1y0 / (double)cnt);
	printf("cntx0y1 = %d (%.010lf)\n", cntx0y1, cntx0y1 / (double)cnt);

	return 0;
}
#endif