原文：https://www.cnblogs.com/machao/p/5882302.html
参考：
https://blog.csdn.net/peisir/article/details/54799662
参考博文： volatile，让我保持原样
device.c
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
int g_ready = 0;
//int volatile g_ready = 0;
void* init_device(void* args)
{
sleep(5);
g_ready = 1;
printf("init_device() - device status : g_ready = %d
", g_ready);
}
void launch_device()
{
pthread_t tid = 0;
pthread_create(&tid, NULL, init_device, NULL);
}
mai#include <stdio.h>
#include <pthread.h>
extern volatile const int g_ready;
//extern const volatile int g_ready;
int main()
{
launch_device();
while( g_ready == 0 )
{
sleep(1);
printf("main() - launching device : g_ready = %d
", g_ready);
}
printf("main() - device status : g_ready = %d
", g_ready);
return 0;
使用带优化选项的编译命令：
gcc -O3 main.c device.c -lpthread -o test.out
观察结论：
1、volatile 和const只在本文件有效
2、将main.c中的
extern volatile const int g_ready改为
extern volatile const char g_ready,依然可以编译通过。参考《 volatile，让我保持原样》中关于编译链接过程的描述，编译只是针对本文件。