linux c 编程，while循环里，判断标志位的值，是变量的值是0，就打印出来，并赋值1，定时器里每1s，给变量直接赋值0，
但是定时器中修改了值之后，while里进不了if，必须要加个usleep延时才行
代码：
void signal_handler(int m)
{
printf("******m_socket_flag = %d \n", m_socket_flag);
m_socket_flag = 0;
}
int main(int argc, char *argv[])
{
signal(SIGALRM, signal_handler);
set_timer(1); //定时1s，并在1s后启动
int h;
while (1)
{
usleep(1);
if (0 == m_socket_flag)
{
h++;
printf("m_socket_flag = %d /// h = %d\n", m_socket_flag,h);
m_socket_flag = 1;
}
}
}
加入了usleep(1)延时1us，则输出正常：
m_socket_flag = 0 /// h = 1
******m_socket_flag = 1
m_socket_flag = 0 /// h = 2
******m_socket_flag = 1
m_socket_flag = 0 /// h = 3
******m_socket_flag = 1
m_socket_flag = 0 /// h = 4
******m_socket_flag = 1
m_socket_flag = 0 /// h = 5
******m_socket_flag = 1
m_socket_flag = 0 /// h = 6
******m_socket_flag = 1
m_socket_flag = 0 /// h = 7
******m_socket_flag = 1
m_socket_flag = 0 /// h = 8
去掉usleep之后，就进不了if了：
m_socket_flag = 0 /// h = 1
******m_socket_flag = 1
******m_socket_flag = 0
******m_socket_flag = 0
******m_socket_flag = 0
******m_socket_flag = 0
******m_socket_flag = 0
******m_socket_flag = 0
******m_socket_flag = 0
请教各位，这是什么原因呢？一是想知道原因，二是发现即使有usleep的情况下，时间长了，也有一定概率，不能进if
