alarm和pause函数

末蓝、 2022-06-12 12:50 182阅读 0赞

NOTE:部分文字说明出自《UNIX环境高级编程》

1. alarm函数

每个进程只能有一个闹钟时钟。如果在调用alarm时，以前已为该进程设置过时钟，而且它还没超时，则将该闹钟的余值作为本次alarm函数调用的值返回。以前登记的时钟则被新值代替。如果闹钟到时，默认操作为终止该进程，但是大多数进程会捕捉该信号然后进行相应的处理。

代码说明1：

\#include "unistd.h"  
\#include "stdio.h"  
  
int main()  
\{  
int ret = 0;  
int alarm\_num = 10,sleep\_num = 3;  
  
printf("Begin to first count alarm %d seconds.\\n",alarm\_num);  
ret = alarm(alarm\_num);  
printf("Begin to sleep count %d seconds.\\n",sleep\_num);  
sleep(sleep\_num);  
printf("End sleep,first\_ret = %d\\n",ret);  
 alarm\_num = 2;  
printf("Begin to second count alarm %d seconds.\\n",alarm\_num);  
 ret = alarm(alarm\_num); //重新赋值给闹钟2秒  
printf("second ret = %d\\n",ret);  
while(1);  
return 0;  
\}  
  
编译：

\[elbort@elbort test1\]$ gcc -Wall -o test test.c  
  
结果显示：

\[elbort@elbort test1\]$ ./test  
Begin to first count alarm 10 seconds.  
Begin to sleep count 3 seconds.  
End sleep,first\_ret = 0  
Begin to second count alarm 2 seconds.  
second ret = 7 //重新给闹钟赋值前，闹钟运行了3秒，所以返回值为10-3=7。

注意：这里等了两秒  
闹钟 //闹钟到时，默认终止该进程  
\[elbort@elbort test1\]$

代码说明2：添加对闹钟信号处理

\#include "unistd.h"  
\#include "stdio.h"  
\#include "signal.h"  
\#include "stdlib.h"  
void sig\_alrm()  
\{  
printf("catch a alarm signal!\\n");  
exit(0);  
\}  
  
int main()  
\{  
int ret = 0;  
int alarm\_num = 10,sleep\_num = 3;  
signal(SIGALRM,sig\_alrm);  
printf("Begin to first count alarm %d seconds.\\n",alarm\_num);  
ret = alarm(alarm\_num);  
printf("Begin to sleep cont %d seconds.\\n",sleep\_num);  
sleep(sleep\_num);  
printf("End sleep,first\_ret = %d\\n",ret);  
alarm\_num = 2;  
printf("Begin to second count alarm %d seconds.\\n",alarm\_num);  
ret = alarm(alarm\_num);  
printf("second ret = %d\\n",ret);  
while(1);  
return 0;  
\}

运行结果：

\[elbort@elbort test1\]$ ./test  
Begin to first count alarm 10 seconds.  
Begin to sleep cont 3 seconds.  
End sleep,first\_ret = 0  
Begin to second count alarm 2 seconds.  
second ret = 7  
catch a alarm signal! //进入获得闹钟信号处理函数  
\[elbort@elbort test1\]$

如果有以前为进程登记的尚未超时的闹钟时钟，而且本次调用的seconds值是0，则取消以前的闹钟，其余值仍作为alarm函数的返回值。

代码说明：

\#include "unistd.h"  
\#include "stdio.h"  
  
int main()  
\{  
int ret;  
ret = alarm(8);  
printf("First ret = %d\\n",ret);  
printf("Here sleep 2 seconds.\\n");  
sleep(2);  
ret = alarm(0);  
printf("Second ret = %d\\n",ret);  
printf("Here sleep 10 seconds.\\n");  
sleep(10);  
printf("The alarm is cancle.The process don't catch the SIGALRM\\n");  
return 0;  
\}  
  
运行结果：

\[elbort@elbort test1\]$ ./test1  
First ret = 0  
Here sleep 2 seconds.  
Second ret = 6  
Here sleep 10 seconds.  
The alarm is cancle.The process don't catch the SIGALRM  
\[elbort@elbort test1\]$

2.pause函数

2. pause函数:

pause函数使调用进程挂起, 直到捕捉到一个信号. 它的原型如下:

\#include  < unistd.h >   
  
 int  pause();  
  
返回 \- 1 , 并将errno设置为EINTR.

这个函数很简单, 由字面意思就可以理解出来"暂停". pause只有在执行了一个信号处理程序并从其返回时, pause才返回.

代码说明：

\#include "unistd.h"  
\#include "stdio.h"  
\#include "signal.h"  
\#include "stdlib.h"  
\#include <sys/types.h>  
  
pid\_t main\_pid;  
void sig\_alrm()  
\{  
printf("catch a alarm signal!\\n");  
kill(main\_pid,SIGCONT);  
\}  
int main()  
\{  
  
int alarm\_num = 5;  
main\_pid = getpid();  
signal(SIGALRM,sig\_alrm);  
printf("Begin to count alarm %d seconds.\\n",alarm\_num);  
alarm(alarm\_num);  
pause();  
printf("main catch SIGCONT.\\n");  
return 0;  
\}  
  
结果显示：

\[elbort@elbort test1\]$ ./h  
Begin to count alarm 5 seconds.  
catch a alarm signal!  
main catch SIGCONT.  
\[elbort@elbort test1\]$