10 信号处理5

1. 多次设置进程的处理方式时，进程会使用最新的处理方式：

实例中，alarm使用默认处理方式。

#include "stdio.h"
#include "sys/types.h"
#include "signal.h"
#include "stdio.h"
#include "stdlib.h"
void myfun(int signum)
{
  int i;
  i=0;
  while(i < 10)
  {
printf("process signal signum=%d\n",signum);
sleep(1);
i++;
  }
  return; // return main
}
int main()
{ 
  int i;
  i=0;
  signal(14,myfun);
  printf("alarm before\n");
  alarm(9);
  printf("alarm after\n");
  signal(14,SIG_IGN);
  signal(14,SIG_DFL);
  while(i< 20)
  {
i++;
sleep(1);
printf("process things,i=%d\n",i);
  }
  return 0;
}

执行结果：

alex@alex-virtual-machine:/extra/process/010$ gcc signal_2.c
alex@alex-virtual-machine:/extra/process/010$ ./a.out
alarm before
alarm after
process things,i=1
process things,i=2
process things,i=3
process things,i=4
process things,i=5
process things,i=6
process things,i=7
process things,i=8
Alarm clock

2. 示例二，进程间信号通信：子进程向父进程发送信号：

a. exit函数传递的信号是SIGCHLD，17

b. 子进程结束时，父进程收到exit信号，通过wait(NULL)函数回收资源。

#include "stdio.h"
#include "sys/types.h"
#include "signal.h"
#include "stdio.h"
#include "stdlib.h"
void myfun(int signum)
{
  int i;
  i=0;
  while(i <5)
  {
printf("receive signum=%d,i=%d\n",signum,i);
sleep(1);
i++;
  }
  return;
}
void myfun1(int signum)
{
  printf("receive signum=%d\n",signum);
  wait(NULL);
  return ;
}

int main()
{
  pid_t pid;
  pid=fork();
  if(pid > 0 )
  {
int i;
i=0;
signal(10,myfun);
signal(17,myfun1);
while(1)
{
     printf("parent process things,i=%d\n",i);
 sleep(1);
 i++;
}
  }
  if(pid ==  0)
  {
sleep(10);
kill(getppid(),10);
sleep(10);
exit(0);//kill(getppid(),17)
  }
  return 0;
}

执行结果：

alex@alex-virtual-machine:/extra/process/010$ gcc signal_3.c
alex@alex-virtual-machine:/extra/process/010$ ls
a.out  signal_2.c  signal_3.c
alex@alex-virtual-machine:/extra/process/010$ ./a.out
parent process things,i=0
parent process things,i=1
parent process things,i=2
parent process things,i=3
parent process things,i=4
parent process things,i=5
parent process things,i=6
parent process things,i=7
parent process things,i=8
parent process things,i=9
receive signum=10,i=0
receive signum=10,i=1
receive signum=10,i=2
receive signum=10,i=3
receive signum=10,i=4
parent process things,i=10
parent process things,i=11
parent process things,i=12
parent process things,i=13
parent process things,i=14
receive signum=17
parent process things,i=15
parent process things,i=16
parent process things,i=17
^C