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library: make dynamic buffer management more efficient

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When dynamic buffers were recently introduced for read
of the status, stat and statm subdirectories one extra
call to read() was required for end-of-file detection.

This patch avoids most all such extra calls to read().

Additionally, the frequency of memory reallocations is
reduced by overallocating each increase more than 25%.

Reference)s):
commit a45dace4b82c9cdcda7020ca5665153b1e81275f

Signed-off-by: Jim Warner <james.warner@comcast.net>
Signed-off-by: Craig Small <csmall@enc.com.au>
This commit is contained in:
Jim Warner 2013-03-29 00:00:00 -05:00 committed by Craig Small
parent c2707dc2d7
commit 6d605f521c
1 changed files with 8 additions and 5 deletions
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13
proc/readproc.c
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@ -534,28 +534,31 @@ static void statm2proc(const char* s, proc_t *restrict P) {
static int file2str(const char *directory, const char *what, struct utlbuf_s *ub) {
#define readMAX 4096
#define buffMIN (tot_read + num + 1) // +1 for the '\0' delimiter
#define buffMIN (tot_read + num + 1) // +1 for the '\0' delimiter
#define buffGRW (30 + (buffMIN * 5) / 4) // grow by more than 25%
char path[PROCPATHLEN], chunk[readMAX];
int fd, num, tot_read = 0;
int fd, num, eof = 0, tot_read = 0;
/* on first use we preallocate a buffer of minimum size to emulate
former 'local static' behavior -- even if this read fails, that
buffer will likely soon be used for another sudirectory anyway */
buffer will likely soon be used for another subdirectory anyway */
if (ub->buf) ub->buf[0] = '\0';
else ub->buf = xcalloc((ub->siz = readMAX));
sprintf(path, "%s/%s", directory, what);
if (-1 == (fd = open(path, O_RDONLY, 0))) return -1;
while (0 < (num = read(fd, chunk, readMAX))) {
while (!eof && 0 < (num = read(fd, chunk, readMAX))) {
if (ub->siz < buffMIN)
ub->buf = xrealloc(ub->buf, (ub->siz = buffMIN));
ub->buf = xrealloc(ub->buf, (ub->siz = buffGRW));
memcpy(ub->buf + tot_read, chunk, num);
tot_read += num;
eof = (num < readMAX);
};
ub->buf[tot_read] = '\0';
close(fd);
return tot_read;
#undef readMAX
#undef buffMIN
#undef buffGRW
}
static char** file2strvec(const char* directory, const char* what) {