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

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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
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43
od.c
View File

@@ -1,8 +1,10 @@
/* See LICENSE file for copyright and license details. */
#include <fcntl.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "queue.h"
#include "util.h"
@@ -124,20 +126,23 @@ once:
}
}
static void
od(FILE *fp, char *fname, int last)
static int
od(int fd, char *fname, int last)
{
static unsigned char *line;
static size_t lineoff;
static off_t addr;
unsigned char buf[BUFSIZ];
size_t i, n, size = sizeof(buf);
size_t i, size = sizeof(buf);
ssize_t n;
while (skip - addr > 0) {
n = fread(buf, 1, MIN(skip - addr, sizeof(buf)), fp);
n = read(fd, buf, MIN(skip - addr, sizeof(buf)));
if (n < 0)
weprintf("read %s:", fname);
if (n <= 0)
return n;
addr += n;
if (feof(fp) || ferror(fp))
return;
}
if (!line)
line = emalloc(linelen);
@@ -145,7 +150,7 @@ od(FILE *fp, char *fname, int last)
for (;;) {
if (max >= 0)
size = MIN(max - (addr - skip), size);
if (!(n = fread(buf, 1, size, fp)))
if ((n = read(fd, buf, size)) <= 0)
break;
for (i = 0; i < n; i++, addr++) {
line[lineoff++] = buf[i];
@@ -155,10 +160,15 @@ od(FILE *fp, char *fname, int last)
}
}
}
if (n < 0) {
weprintf("read %s:", fname);
return n;
}
if (lineoff && last)
printline(line, lineoff, addr - lineoff);
if (last)
printline((unsigned char *)"", 0, addr);
return 0;
}
static int
@@ -196,7 +206,7 @@ usage(void)
int
main(int argc, char *argv[])
{
FILE *fp;
int fd;
struct type *t;
int ret = 0, len;
char *s;
@@ -293,25 +303,26 @@ main(int argc, char *argv[])
linelen *= 2;
if (!argc) {
od(stdin, "<stdin>", 1);
if (od(0, "<stdin>", 1) < 0)
ret = 1;
} else {
for (; *argv; argc--, argv++) {
if (!strcmp(*argv, "-")) {
*argv = "<stdin>";
fp = stdin;
} else if (!(fp = fopen(*argv, "r"))) {
weprintf("fopen %s:", *argv);
fd = 0;
} else if ((fd = open(*argv, O_RDONLY)) < 0) {
weprintf("open %s:", *argv);
ret = 1;
continue;
}
od(fp, *argv, (!*(argv + 1)));
if (fp != stdin && fshut(fp, *argv))
if (od(fd, *argv, (!*(argv + 1))) < 0)
ret = 1;
if (fd != 0)
close(fd);
}
}
ret |= fshut(stdin, "<stdin>") | fshut(stdout, "<stdout>") |
fshut(stderr, "<stderr>");
ret |= fshut(stdout, "<stdout>") | fshut(stderr, "<stderr>");
return ret;
}