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Full Discussion: semaphore access speed
Top Forums Programming semaphore access speed Post 302237918 by otheus on Thursday 18th of September 2008 04:10:44 PM
Old 09-18-2008
Here's one answer: your time measurement is buggy. See man on ftime() under Linux:

Quote:
This function is obsolete. Don't use it. If the time in seconds suffices, time(2) can
be used; gettimeofday(2) gives microseconds; clock_gettime(3) gives nanoseconds but
is not yet widely available.

Under libc4 and libc5 the millitm field is meaningful. But early glibc2 is buggy and
returns 0 there; glibc 2.1.1 is correct again.
 

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FTIME(3)						     Linux Programmer's Manual							  FTIME(3)

NAME
ftime - return date and time SYNOPSIS
#include <sys/timeb.h> int ftime(struct timeb *tp); DESCRIPTION
This function returns the current time as seconds and milliseconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC). The time is returned in tp, which is declared as follows: struct timeb { time_t time; unsigned short millitm; short timezone; short dstflag; }; Here time is the number of seconds since the Epoch, and millitm is the number of milliseconds since time seconds since the Epoch. The timezone field is the local timezone measured in minutes of time west of Greenwich (with a negative value indicating minutes east of Green- wich). The dstflag field is a flag that, if nonzero, indicates that Daylight Saving time applies locally during the appropriate part of the year. POSIX.1-2001 says that the contents of the timezone and dstflag fields are unspecified; avoid relying on them. RETURN VALUE
This function always returns 0. (POSIX.1-2001 specifies, and some systems document, a -1 error return.) ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7). +----------+---------------+---------+ |Interface | Attribute | Value | +----------+---------------+---------+ |ftime() | Thread safety | MT-Safe | +----------+---------------+---------+ CONFORMING TO
4.2BSD, POSIX.1-2001. POSIX.1-2008 removes the specification of ftime(). This function is obsolete. Don't use it. If the time in seconds suffices, time(2) can be used; gettimeofday(2) gives microseconds; clock_gettime(2) gives nanoseconds but is not as widely available. BUGS
Early glibc2 is buggy and returns 0 in the millitm field; glibc 2.1.1 is correct again. SEE ALSO
gettimeofday(2), time(2) COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. GNU
2017-09-15 FTIME(3)
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