From: lm@mcvoy.com (Larry McVoy)
Subject: [TUHS] the sin of buffering [offshoot of excise process from a pipeline]
Date: Mon, 14 Jul 2014 19:40:42 -0700 [thread overview]
Message-ID: <20140715024042.GD13698@mcvoy.com> (raw)
In-Reply-To: <201407150231.s6F2VRK0022875@coolidge.cs.dartmouth.edu>
On Mon, Jul 14, 2014 at 10:31:27PM -0400, Doug McIlroy wrote:
> > Err, why is buffering data in the process a sin? (Or was this just a
> humourous aside?)
>
> Process A spawns process B, which reads stdin with buffering. B gets
> all it deserves from stdin and exits. What's left in the buffer,
> intehded for A, is lost. Sinful.
It really depends on what you want. That buffering is a big win for
some use cases. Even on today's processors reading a byte at a time via
read(2) is costly. Like 5000x more costly on the laptop I'm typing on:
calvin:~/tmp lmdd opat=1 move=100m of=XXX
104.8576 MB in 0.1093 secs, 959.5578 MB/sec
calvin:~/tmp time a.out fd < XXX
real 0m14.754s
user 0m1.516s
sys 0m13.201s
calvin:~/tmp time a.out stdio < XXX
real 0m0.003s
user 0m0.000s
sys 0m0.000s
calvin:~/tmp bc
14.754/.003
4918.00000000000000000000
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define unless(x) if (!(x))
#define streq(a, b) !strcmp(a, b)
main(int ac, char **av)
{
char c;
unless (ac == 2) exit(1);
if (streq(av[1], "stdio")) {
while ((c = fgetc(stdin)) != EOF)
;
} else {
while (read(0, &c, 1) == 1)
;
}
exit(0);
}
next prev parent reply other threads:[~2014-07-15 2:40 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-15 2:31 Doug McIlroy
2014-07-15 2:40 ` Larry McVoy [this message]
2014-07-15 18:55 ` scj
2014-07-15 23:43 Doug McIlroy
2014-07-16 0:32 ` Larry McVoy
2014-07-16 3:53 ` John Cowan
2014-07-16 4:05 ` Larry McVoy
2014-07-16 6:03 ` John Cowan
2014-07-16 14:30 ` Larry McVoy
2014-07-16 14:56 ` Dan Cross
2014-07-16 15:41 ` Larry McVoy
2014-07-16 21:46 Noel Chiappa
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