12-06-2005
Quote:
Originally Posted by Bhups
cum to the rescue sir
....a beginner conjures ur help
...???
You can't squeeze blood from a stone. The standard unix date command doesn't do milliseconds. Posix says: "The resolution of the system clock is unspecified.", but they make it clear elsewhere that a resolution of at least one second is required. Posix does demand that the system clock system calls supply an interface that supports microseconds. But you may not write a portable unix program that needs milliseconds. But as a practical matter, all modern systems will have at least millisecond resolution. But you won't find a standard unix utiliity that supports milliseconds. So you need another program to call from your shell script. Either GNU date or that little utility in the linked thread will do. And don't expect it to work well on any real old unix systems. In fact, even on a modern computer, several milliseconds may occur between the time your script obtains the milliseconds and communicates the timestamp to the outside world. Scripts need to fork and exec external programs to do stuff. That is not conducive to millisecond resolution.You may need to write your program in completely in C and/or use realtime extentions.
(Hmmmm: Vino is dividing the output of %N by 1000000 which implies that %N returns
nanoseconds. I'll have to look into that. It's not obvious how to get nanoseconds....)
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LEARN ABOUT MOJAVE
clock_getres
CLOCK_GETTIME(3) BSD Library Functions Manual CLOCK_GETTIME(3)
NAME
clock_gettime, clock_settime, clock_getres, clock_gettime_nsec_np -- get/set date and time
SYNOPSIS
#include <time.h>
int
clock_gettime(clockid_t clock_id, struct timespec *tp);
int
clock_settime(clockid_t clock_id, const struct timespec *tp);
int
clock_getres(clockid_t clock_id, struct timespec *tp);
uint64_t
clock_gettime_nsec_np(clockid_t clock_id);
DESCRIPTION
The clock_gettime() and clock_settime() functions allow the calling process to retrieve or set the value used by a clock which is specified
by clock_id.
clock_id can be a value from one of 5 predefined values:
CLOCK_REALTIME the system's real time (i.e. wall time) clock, expressed as the amount of time since the Epoch. This is the same as the
value returned by gettimeofday(2).
CLOCK_MONOTONIC clock that increments monotonically, tracking the time since an arbitrary point, and will continue to increment while the
system is asleep.
CLOCK_MONOTONIC_RAW
clock that increments monotonically, tracking the time since an arbitrary point like CLOCK_MONOTONIC. However, this clock
is unaffected by frequency or time adjustments. It should not be compared to other system time sources.
CLOCK_MONOTONIC_RAW_APPROX
like CLOCK_MONOTONIC_RAW, but reads a value cached by the system at context switch. This can be read faster, but at a
loss of accuracy as it may return values that are milliseconds old.
CLOCK_UPTIME_RAW clock that increments monotonically, in the same manner as CLOCK_MONOTONIC_RAW, but that does not increment while the sys-
tem is asleep. The returned value is identical to the result of mach_absolute_time() after the appropriate mach_timebase
conversion is applied.
CLOCK_UPTIME_RAW_APPROX
like CLOCK_UPTIME_RAW, but reads a value cached by the system at context switch. This can be read faster, but at a loss
of accuracy as it may return values that are milliseconds old.
CLOCK_PROCESS_CPUTIME_ID
clock that tracks the amount of CPU (in user- or kernel-mode) used by the calling process.
CLOCK_THREAD_CPUTIME_ID
clock that tracks the amount of CPU (in user- or kernel-mode) used by the calling thread.
The structure pointed to by tp is defined in <sys/time.h> as:
struct timespec {
time_t tv_sec; /* seconds */
long tv_nsec; /* and nanoseconds */
};
Only the CLOCK_REALTIME clock can be set, and only the superuser may do so.
The resolution of a clock is returned by the clock_getres() call. This value is placed in a (non-null) *tp. This value may be smaller than
the actual precision of the underlying clock, but represents a lower bound on the resolution.
As a non-portable extension, the clock_gettime_nsec_np() function will return the clock value in 64-bit nanoseconds.
RETURN VALUES
A 0 return value indicates that the call succeeded. A -1 return value indicates an error occurred, and in this case an error code is stored
into the global variable errno. For clock_gettime_nsec_np() a return value of non-0 indicates success. A 0 return value indicates an error
occurred and an error code is stored in errno.
ERRORS
clock_gettime(), clock_settime(), clock_getres(), and clock_gettime_nsec_np() will fail if:
[EINVAL] clock_id is not a valid value.
[EFAULT] The tp argument address referenced invalid memory.
In addition, clock_settime() may return the following errors:
[EPERM] A user other than the superuser attempted to set the time.
[EINVAL] clock_id specifies a clock that isn't settable, tp specifies a nanosecond value less than zero or greater than 1000 mil-
lion, or a value outside the range of the specified clock.
SEE ALSO
date(1), getitimer(2), gettimeofday(2),
HISTORY
These functions first appeared in Mac OSX 10.12
STANDARDS
The clock_gettime(), clock_settime(), and clock_getres() system calls conform to IEEE Std 1003.1b-1993 (``POSIX.1'').
cleck_gettime_nsec_np() is a non-portable Darwin extension. The clock IDs CLOCK_MONOTONIC_RAW and CLOCK_UPTIME_RAW are extensions to the
POSIX interface.
BSD
January 26, 2016 BSD