writing to a file using print

[Brad.Walker]

I am attempting to write to a file use the print keyword. I'm doing the following:

     print $test_file $random_data

$random_data is a 1MB string and $test_file is the file handle that was opened up using the 3 argument version of open.

The problem that I'm encountering is the Perl interpreter is breaking this large write into 4K writes at the system call level. I don't really want this because I'm trying to do some NFS performance measurements and the breakup of writes is causing me problems. I know that I could use syswrite, but was hoping to stay away from this.

Thanks.
-brad w.

[dorko]

Brad,

Looks like you're "suffering from buffering".

Try turning buffering off by adding the following line before your print statement:


$|++;

Cheers,

Brent

[geekphilosopher]

Or, if you want to follow the lead of The Damian in Perl Best Practices, you can do:

$| = 1;

[dorko]

This whole discussion gives me nasty flashbacks to a time when I couldn't have been more wrong. At that point I switched from $| = 1; to $|++;.

I've mostly gotten over it... :)

Cheers,

Brent

[ikegami]

Do you get the same problem with syswrite? It doesn't use the buffering system used by print. It might still not work, though, because syswrite is not guaranteed to write everything it is asked to write (in a single call).

my $written = syswrite($test_file, $buf, length($buf));
die("Unable to write to file: $!\n")
   if not defined $written;
die("Unable to write whole string in one call\n")
   if $written != length($buf);

For comparison, syswrite is normally used as follows:

my $offset   = 0;
my $to_write = length($buf);
while ($to_write > 0) {
   my $written = syswrite($test_file, $buf, $to_write, $offset);
   die("Unable to write to file: $!\n")
      if not defined $written;
   $to_write -= $written;
   $offset   += $written;
}