When sending SIGHUP to bgwriter

Hi:

I am now reading the bgwriter.c’s source code, and found :

pqsignal(SIGHUP, BgSigHupHandler); /* set flag to read config file */

So I tried to use Kill –s SIGHUP to confirm it.

I found that if I directly send SIGHUP to bgwriter, it has no response.
If I send SIGHUP to its parent—postgres, I will found the postresql.conf
really re-read.

[root(at)localhost ~]# ps -ef|grep post
postgres 4628 4535 0 13:30 pts/1 00:00:00 ./postgres -D
/usr/local/pgsql/data
postgres 4630 4628 0 13:30 ? 00:00:00 postgres: checkpointer
process
postgres 4631 4628 0 13:30 ? 00:00:00 postgres: writer process

postgres 4632 4628 0 13:30 ? 00:00:00 postgres: wal writer
process
postgres 4633 4628 0 13:30 ? 00:00:00 postgres: autovacuum
launcher process
postgres 4634 4628 0 13:30 ? 00:00:00 postgres: stats collector
process
postgres 4689 4592 0 13:31 pts/2 00:00:00 ./psql
postgres 4690 4628 0 13:31 ? 00:00:00 postgres: postgres postgres
[local] idle
root 4694 4638 0 13:31 pts/3 00:00:00 grep post
When using
# kill -s SIGHUP 4631
I found in psql, "show bgwriter_delay" is same to original value(200ms).

When using
# kill -s SIGHUP 4628
I found in psql, "show bgwriter_delay" showed the newly saved value of
postgresql.conf(300ms)

At the same time , postgres in background print the follwing output:
LOG: received SIGHUP, reloading configuration files
LOG: parameter "bgwriter_delay" changed to "300ms"

What confused me is that postgres as parent, can transfer the SIGHUP, and
call the BgSigHupHandler, but why directly send SIGHUP to bgwriter does not
work?
Is there some place which hold code like "execl" and make bgwriter does not
response to SIGHUP directly?

I have test simple parent and child like following, both parent and child
will response to signal.

//////////////////////////////////////////
[root(at)localhost test]# cat testfork.c
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <signal.h>
int test=0;
void sighandler(int sig);
int main()
{
signal(SIGHUP,sighandler);
pid_t pid;

pid=fork();
if (pid < 0)
{
printf("Fork failured!\n");
}else if (pid == 0)
{
printf("This is child thread!\n");
test=100;
for (;;)
{
sleep(1);
}
}else
{
printf("Child process %d created!\n", pid);
for (;;)
{
sleep(1);
}
}
return 0;
}
void sighandler(int sig)
{
fprintf(stderr,"my test is:%d\n",test);
}
[root(at)localhost test]#./testfork.o
[root(at)localhost ~]# ps -ef|grep testfork
root 6157 5297 0 17:35 pts/6 00:00:00
./testfork.o
root 6158 6157 0 17:35 pts/6 00:00:00
./testfork.o
root 6160 5479 0 17:35 pts/7 00:00:00
grep testfork
[root(at)localhost ~]# kill -s SIGHUP 6158
[root(at)localhost ~]#my test is:100

[root(at)localhost ~]# kill -s SIGHUP 6157
[root(at)localhost ~]#my test is 0
//////////////////////////////////////////