sigaction 和 signal 函数

喜欢ヅ旅行 2022-06-12 13:22 195阅读 0赞

1.sigaction 函数

NAME  
sigaction - examine and change a signal action  
  
SYNOPSIS  
\#include <signal.h>  
  
int sigaction(int sig,  const struct sigaction \* act, struct sigaction \* oact);

### Parameters ###

***sig***

(Input) A signal from the list defined in [ ControlSignals Table][ControlSignals Table] .

***\*act***

(Input) A pointer to the sigaction structure that describesthe action to be taken for the signal. Can be NULL.

If *act* is a NULL pointer, signal handling is unchanged. **sigaction()** can be used to inquire about the current handling ofsignal*sig*.

If *act* is not NULL, the action specified in the sigaction structure becomes the new action associated with*sig*.

***\*oact***

(Output) A pointer to a storage location where **sigaction()**can store a sigaction structure. This structure contains theaction currently associated with *sig*. Can be NULL.

If *oact* is a NULL pointer, **sigaction()** does notstore this information.

structure sigaction：

<table> 
 <tbody> 
  <tr> 
   <th align="center"><strong>Member Type</strong></th> 
   <th align="center"><strong>Member Name</strong></th> 
   <th align="center"><strong>Description</strong></th> 
  </tr> 
  <tr> 
   <td align="left">void(*) (int)</td> 
   <td align="left">sa_handler</td> 
   <td align="left">Pointer to a signal-catching function or one of the macros SIG_IGN or SIG_DFL.</td> 
  </tr> 
  <tr> 
   <td align="left">sigset_t</td> 
   <td align="left">sa_mask</td> 
   <td align="left">Additional set of signals to<span style="color:#CC0000"> be blocked during execution of signal-catching function.</span></td> 
  </tr> 
  <tr> 
   <td align="left">int</td> 
   <td align="left">sa_flags</td> 
   <td align="left">Special flags to affect behaviour of signal.</td> 
  </tr> 
  <tr> 
   <td align="left">void(*) (int, siginfo_t *, void *)</td> 
   <td align="left">sa_sigaction</td> 
   <td align="left">Pointer to a signal-catching function.</td> 
  </tr> 
 </tbody> 
</table>

代码说明：

\#include "signal.h"  
\#include "stdio.h"  
\#include "unistd.h"  
  
  
void fun\_int()  
\{  
printf("\\n\*\*\*\*\*\*\*fun\_int catch SIGINT\*\*\*\*\*\\n");  
printf("I'm sleeping......\\n");  
sleep(10);  
printf("\\n\*\*\*\*\*\*\*\*\*leave fun\_int\*\*\*\*\*\*\*\*\*\*\\n");  
\}  
  
int main()  
\{  
struct sigaction new,old;  
new.sa\_handler = &fun\_int;  
sigfillset(&new.sa\_mask);  
sigdelset(&new.sa\_mask,SIGINT);  
sigaction(SIGINT,&new,NULL);  
printf("Initial finish, please send the signal\\n");  
while(1);  
\}

结果显示1：

\[elbort@elbort test1\]$ ./test  
Initial finish, please send the signal  
^C //接收到SIGINT，调用相应的函数  
\*\*\*\*\*\*\*fun\_int catch SIGINT\*\*\*\*\*  
I'm sleeping......  
^\\^\\^C^C //设置了阻塞，其他信号只会阻塞在执行函数里  
\*\*\*\*\*\*\*\*\*leave fun\_int\*\*\*\*\*\*\*\*\*\*  
  
\*\*\*\*\*\*\*fun\_int catch SIGINT\*\*\*\*\* //退出信号执行函数，之前在执行函数中的信号被释放，首先对比注册登记信号函数，故虽然SIGQUIT首先接收，还是执行SIGINT  
I'm sleeping......  
  
\*\*\*\*\*\*\*\*\*leave fun\_int\*\*\*\*\*\*\*\*\*\*  
退出(吐核) //信号只会登记一次，重复无效，执行完SIGINT，现在轮到SIGQUIT  
\[elbort@elbort test1\]$

结果显示2：

\[elbort@elbort test1\]$ ./test  
Initial finish, please send the signal  
^\\退出(吐核)  //设置的阻塞只会在执行信号函数里  
\[elbort@elbort test1\]$

2.signal函数

功能和sigaction类似，是sigaction的简化版，不能对执行函数运行时进行信号屏蔽。

代码说明：

\#include "signal.h"  
\#include "stdio.h"  
\#include "unistd.h"  
  
void fun\_int()  
\{  
printf("\\n\*\*\*\*\*\*\*fun\_int catch SIGINT\*\*\*\*\*\\n");  
printf("I'm sleeping......\\n");  
sleep(10);  
printf("\\n\*\*\*\*\*\*\*\*\*leave fun\_int\*\*\*\*\*\*\*\*\*\*\\n");  
\}  
  
  
int main()  
\{  
signal(SIGINT,fun\_int);  
printf("Initial finish, please send the signal\\n");  
while(1);  
  
\}

结果显示：

\[elbort@elbort test1\]$ ./test  
Initial finish, please send the signal  
^C  
\*\*\*\*\*\*\*fun\_int catch SIGINT\*\*\*\*\*  
I'm sleeping......  
^C^C //重复发送SIGINT信号，重复运行该执行函数（据说版本不同，这里现象不同，网上说有的重复调用会调用默认执行函数，在这则是终止该进程，但我的测试版本没出现这种情况）  
\*\*\*\*\*\*\*\*\*leave fun\_int\*\*\*\*\*\*\*\*\*\*  
  
\*\*\*\*\*\*\*fun\_int catch SIGINT\*\*\*\*\*  
I'm sleeping......  
^C^C^\\退出(吐核) //接收到SIGQUIT直接退出  
\[elbort@elbort test1\]$

个人总结：

在运行上面代码，我发现当进程在调用接收到的signal函数时，向该进程再次发送同样的信号（在本例中该信号是SIGINT），该进程并不会立刻对该信号进行处理，只是将其进行压栈，等到信号函数完成后退出再检测是否调用该信号函数。而且在信号阻塞期间接收的各种信号，不论先后，当信号函数结束后，会优先检查信号注册函数表，查看是否有相匹配的信号处理，如有则调用该函数，如无则默认处理阻塞后被释放的信号（可看sigaction 结果显示1）。

[ControlSignals Table]: http://publib.boulder.ibm.com/infocenter/iseries/v5r3/topic/apis/sigactn.htm#TBLSIGTBL1