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Full Discussion: semaphore access speed
Top Forums Programming semaphore access speed Post 302238477 by otheus on Saturday 20th of September 2008 08:15:24 AM
Old 09-20-2008
Quote:
Originally Posted by jim mcnamara
PS call utimes(struct tms *) to actual times, plus granularity is CLK_TCK, usually way better than time().

gettimeofday can be used to get wall time even more accurately as well. utimes() returns clock_t wall time.
Jim, utimes() doesn't do what you think it does. Gettimeofday is more correct, but then the code is a bit more complicated. Microsecond differences would not produce the disparities in performance he is seeing.
 

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UTIME(2)						     Linux Programmer's Manual							  UTIME(2)

NAME
utime, utimes - change access and/or modification times of an inode SYNOPSIS
#include <sys/types.h> #include <utime.h> int utime(const char *filename, struct utimbuf *buf); #include <sys/time.h> int utimes(char *filename, struct timeval *tvp); DESCRIPTION
utime changes the access and modification times of the inode specified by filename to the actime and modtime fields of buf respectively. If buf is NULL, then the access and modification times of the file are set to the current time. The utimbuf structure is: struct utimbuf { time_t actime; /* access time */ time_t modtime; /* modification time */ }; In the Linux DLL 4.4.1 libraries, utimes is just a wrapper for utime: tvp[0].tv_sec is actime, and tvp[1].tv_sec is modtime. The timeval structure is: struct timeval { long tv_sec; /* seconds */ long tv_usec; /* microseconds */ }; RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately. ERRORS
Other errors may occur. EACCES Permission to write the file is denied. ENOENT filename does not exist. CONFORMING TO
utime: SVr4, SVID, POSIX. SVr4 documents additional error conditions EFAULT, EINTR, ELOOP, EMULTIHOP, ENAMETOOLONG, ENOLINK, ENOTDIR, ENO- LINK, ENOTDIR, EPERM, EROFS. utimes: BSD 4.3 SEE ALSO
stat(2) Linux 1995-06-10 UTIME(2)
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