conterm/libc/nsec.c

66 lines
1.2 KiB
C

#include <u.h>
#include <libc.h>
static uvlong order = (uvlong) 0x0001020304050607ULL;
static void
be2vlong(vlong *to, uchar *f)
{
uchar *t, *o;
int i;
t = (uchar*)to;
o = (uchar*)&order;
for(i = 0; i < 8; i++)
t[o[i]] = f[i];
}
/*
* After a fork with fd's copied, both fd's are pointing to
* the same Chan structure. Since the offset is kept in the Chan
* structure, the seek's and read's in the two processes can
* compete at moving the offset around. Hence the retry loop.
*
* Since the bintime version doesn't need a seek, it doesn't
* have the loop.
*/
vlong
nsec(void)
{
char b[12+1];
static int f = -1;
static int usebintime;
int retries;
vlong t;
if(f < 0){
usebintime = 1;
f = open("/dev/bintime", OREAD|OCEXEC);
if(f < 0){
usebintime = 0;
f = open("/dev/nsec", OREAD|OCEXEC);
if(f < 0)
return 0;
}
}
if(usebintime){
if(read(f, b, sizeof(uvlong)) < 0)
goto error;
be2vlong(&t, (uchar*)b);
return t;
} else {
for(retries = 0; retries < 100; retries++){
if(seek(f, 0, 0) >= 0 && read(f, b, sizeof(b)-1) >= 0){
b[sizeof(b)-1] = 0;
return strtoll(b, 0, 0);
}
}
}
error:
close(f);
f = -1;
return 0;
}