[root@localhost test]# cat bgwriter.c
#include<stdio.h>
#include<stdlib.h>
#include<signal.h>
#include "bgwriter.h"
#include "guc.h"
//some conditions make it change, eg:signal
int BgWriterDelay=100;
void sighandler(int sig);
int main()
{
 
  signal(SIGHUP,sighandler);
  for (;;)
  {
    sleep(1);
  }
}
void sighandler(int sig)
{
  changeDelay();
  fprintf(stderr,"BgWriterDelay is now %d.\n",BgWriterDelay);
  //here I just want to demo, so close it
  exit(0);
}
[root@localhost test]#
/////////////////////////////////////////////////////////////////
下面的 "bgwriter.h" and "guc.h" and "guc.c"，也都是假的。只是为了模拟。
/////////////////////////////////////////////////////////////////
[root@localhost test]# cat bgwriter.h
extern int BgWriterDelay;
[root@localhost test]#

[root@localhost test]# cat guc.h
extern void changeDelay();
[root@localhost test]#cat guc.c
#include "bgwriter.h"
void changeDelay()
{
  //to simulate reading configuration file etc.
  BgWriterDelay=500;
}
[root@localhost test]#
 
/////////////////////////////////////////////////////////////////
给 SIGHUP 信号
 
[root@localhost test]# gcc bgwriter.c guc.c -o bgwriter.o
[root@localhost test]# ./bgwriter.o
[root@localhost ~]# ps -ef|grep bgwriter.o
root      5475  5297  0 15:08 pts/6    00:00:00 ./bgwriter.o
root      5500  5479  0 15:08 pts/7    00:00:00 grep bgwriter.o
[root@localhost ~]# kill -s SIGHUP 5475
[root@localhost ~]#
BgWriterDelay is now 500.
[root@localhost test]#