----- Original Message -----
From: "Will W" <[EMAIL PROTECTED]>
>
> Everyone's fascination with sysread() got me to poking around in the
> camel and cookbook a bit-- and I still can't see the advantage here of
> doing a low-level system call over using read(), which is generally
> buffered for optimal efficiency on whatever system your using. sysread()
> makes a lot of sense on a port, but on a disk file I'm not seeing the
> why of it-- maybe someone will enlighten me.
>
To have a closer look at 'read' versus 'sysread' I did a benchmark test.
I found that 'sysread' took (almost exactly) twice as long as 'read'.
So that was a pretty pertinent point you raised, Will.
Guess I'd have to agree that I, too, don't see the advantage of using
sysread in preference to read.
I also ran the same code using the trick with '$/' (which is also mentioned
in perlvar, btw). Not surprisingly it's pretty much the same speed as
'read'.
Here's a cut'n'paste of both the code I ran and the result I got. Sorry if
it gets wrapped inconveniently.
use Benchmark;
timethese (1, {
'sysread' => 'open (READ, "d:/pscrpt/tab.new")
or die "Cannot open READ: $!";
binmode READ;
while (sysread(READ, $read, 4) == 4) {
$mod = unpack("I", $read);
}
print "$mod\n";
close (READ) or die "Cannot close READ: $!";',
'read' => 'open (READ, "d:/pscrpt/tab.new")
or die "Cannot open READ: $!";
binmode READ;
while (read(READ, $read, 4) == 4) {
$mod = unpack("I", $read);
}
print "$mod\n";
close (READ) or die "Cannot close READ: $!";',
'local' => '{
local $/;
$/ = \4;
open (READ, "d:/pscrpt/tab.new")
or die "Cannot open READ: $!";
binmode READ;
while (<READ>) {
$mod = unpack("I", $_);
}
print "$mod\n";
close (READ) or die "Cannot close READ: $!";
}',
});
##########################################
Benchmark: timing 1 iterations of local, read, sysread...
27112421
local: 25 wallclock secs (24.90 usr + 0.09 sys = 24.98 CPU) @ 0.04/s
(n=1)
(warning: too few iterations for a reliable count)
27112421
read: 26 wallclock secs (26.42 usr + 0.10 sys = 26.52 CPU) @ 0.04/s
(n=1)
(warning: too few iterations for a reliable count)
27112421
sysread: 53 wallclock secs (34.20 usr + 17.39 sys = 51.59 CPU) @ 0.02/s
(n=1)
(warning: too few iterations for a reliable count)
Cheers,
Rob
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