fbt/sbase
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

Don't use buffered IO (fread) when not appropriate

Browse Source 
fread reads the entire requested size (BUFSIZ), which causes tools to
block if only small amounts of data are available at a time. At best,
this causes unnecessary copies and inefficiency, at worst, tools like
tee and cat are almost unusable in some cases since they only display
large chunks of data at a time.
This commit is contained in:
Michael Forney
2017-01-01 17:00:33 -08:00
committed by Anselm R Garbe
parent 5cb3a1eba1
commit 9a3b12525b
5 changed files with 83 additions and 69 deletions
Download Patch File Download Diff File Expand all files Collapse all files

39
tee.c
View File

@@ -1,6 +1,7 @@
/* See LICENSE file for copyright and license details. */
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>
#include "util.h"
@@ -13,14 +14,15 @@ usage(void)
int
main(int argc, char *argv[])
{
FILE **fps = NULL;
size_t i, n, nfps;
int ret = 0, aflag = 0, iflag = 0;
int *fds = NULL;
size_t i, nfds;
ssize_t n;
int ret = 0, aflag = O_TRUNC, iflag = 0;
char buf[BUFSIZ];
ARGBEGIN {
case 'a':
aflag = 1;
aflag = O_APPEND;
break;
case 'i':
iflag = 1;
@@ -31,31 +33,28 @@ main(int argc, char *argv[])
if (iflag && signal(SIGINT, SIG_IGN) == SIG_ERR)
eprintf("signal:");
nfps = argc + 1;
fps = ecalloc(nfps, sizeof(*fps));
nfds = argc + 1;
fds = ecalloc(nfds, sizeof(*fds));
for (i = 0; i < argc; i++) {
if (!(fps[i] = fopen(argv[i], aflag ? "a" : "w"))) {
weprintf("fopen %s:", argv[i]);
if ((fds[i] = open(argv[i], O_WRONLY|O_CREAT|aflag, 0666)) < 0) {
weprintf("open %s:", argv[i]);
ret = 1;
}
}
fps[i] = stdout;
fds[i] = 1;
while ((n = fread(buf, 1, sizeof(buf), stdin))) {
for (i = 0; i < nfps; i++) {
if (fps[i] && fwrite(buf, 1, n, fps[i]) != n) {
fshut(fps[i], (i != argc) ? argv[i] : "<stdout>");
fps[i] = NULL;
while ((n = read(0, buf, sizeof(buf))) > 0) {
for (i = 0; i < nfds; i++) {
if (fds[i] >= 0 && writeall(fds[i], buf, n) < 0) {
weprintf("write %s:", (i != argc) ? argv[i] : "<stdout>");
fds[i] = -1;
ret = 1;
}
}
}
ret |= fshut(stdin, "<stdin>");
for (i = 0; i < nfps; i++)
if (fps[i])
ret |= fshut(fps[i], (i != argc) ? argv[i] : "<stdout>");
if (n < 0)
eprintf("read <stdin>:");
return ret;
}