Re: persistant psql feature suggestion

On Sun, Jun 29, 2003 at 02:15:26PM -0400, Andrew Dunstan wrote:
> We don't need to read and write on the same fd.
> 
> The real right way is to detect when the psql client exits - possible when
> the perl program spawns it, like shown below.
> 
> As always, TIMTOWTDI
> 
> andrew
> 
> --------------------------
> 
> use strict;
> use IO::Handle;
> use POSIX ":sys_wait_h";
> 
> my $curpos;
> my $fifofile = shift || usage();
> my $database = shift || usage();
> 
> open(FILE,$fifofile) || die $!;
> my $psqlpid = open(OUTPIPE,"|-");
> unless (defined($psqlpid)) { die $!; }
> if ($psqlpid == 0)
>   {
>     exec("psql -a $database") || die $!;
>   }
> 
> # must be parent here
> sub REAPER
>   {
>     my $waitedpid;
>     while (($waitedpid = waitpid(-1,WNOHANG)) > 0)
>       {
>  if ($waitedpid == $psqlpid) { exit 0; }
>       }
>     $SIG{CHLD} = \&REAPER;  # loathe sysV
>   }
> 
> $SIG{CHLD} = \&REAPER;
> 
> OUTPIPE->autoflush();
> 
> for (;;)
>   {
>     for ($curpos = tell(FILE); $_ = <FILE>; $curpos = tell(FILE))
>       {
>          print OUTPIPE $_;
>       }
>     sleep(1);
>     seek(FILE, $curpos, 0);
>   }
> 
> 
> sub usage
>   {
>     print STDERR "usage: ",$0," fifofile database\n";
>     exit 1;
>   }

I dropped into autopilot without considering James Pye's
original phrase:

"The ability for psql to remain in the background reading 
from stdin and writing to stdout until explicitly killed"

I went straight to thinking about handling the psql output 
which matched /ERROR/ differently from other output.

I like your solution. But I think I'd code it:

my $psqlpid = open(OUTPIPE,"|-") || die qq(cant fork: $!);

Sometimes I'm too stupid to remember that that perl gives 
you the fork (the knife and the kitchen sink) even if you 
dont realize you asked for it;-)

Cheers,

JPK