dlopen.3: Clarify that constructors are called only when library is first loaded

[thirdparty/man-pages.git] / man3 / clock.3

diff --git a/man3/clock.3 b/man3/clock.3
index b25d2ba23f6b9beb40fb177895e4559ea5e7c4ae..174c18babf3ffdf7993a542424f09b851cc9acaa 100644 (file)
--- a/man3/clock.3
+++ b/man3/clock.3
@@ -1,5 +1,6 @@
-.\" (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
+.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
 .\"
+.\" %%%LICENSE_START(VERBATIM)
 .\" Permission is granted to make and distribute verbatim copies of this
 .\" manual provided the copyright notice and this permission notice are
 .\" preserved on all copies.
@@ -19,34 +20,51 @@
 .\"
 .\" Formatted or processed versions of this manual, if unaccompanied by
 .\" the source, must acknowledge the copyright and authors of this work.
-.\" License.
+.\" %%%LICENSE_END
+.\"
 .\" Modified Sat Jul 24 21:27:01 1993 by Rik Faith (faith@cs.unc.edu)
-.\" Modified 14 Jun 2002, Michael Kerrisk <mtk-manpages@gmx.net>
-.\"    Added notes on differences from other Unix systems with respect to
+.\" Modified 14 Jun 2002, Michael Kerrisk <mtk.manpages@gmail.com>
+.\"    Added notes on differences from other UNIX systems with respect to
 .\"    waited-for children.
-.TH CLOCK 3  2002-06-14 "GNU" "Linux Programmer's Manual"
+.TH CLOCK 3  2017-09-15 "GNU" "Linux Programmer's Manual"
 .SH NAME
-clock \- Determine processor time
+clock \- determine processor time
 .SH SYNOPSIS
 .nf
 .B #include <time.h>
-.sp
+.PP
 .B clock_t clock(void);
 .fi
 .SH DESCRIPTION
 The
 .BR clock ()
 function returns an approximation of processor time used by the program.
-.SH "RETURN VALUE"
+.SH RETURN VALUE
 The value returned is the CPU time used so far as a
-.BR clock_t ;
+.IR clock_t ;
 to get the number of seconds used, divide by
 .BR CLOCKS_PER_SEC .
 If the processor time used is not available or its value cannot
-be represented, the function returns the value (clock_t)\-1.
-.SH "CONFORMING TO"
-C89, C99, POSIX.1-2001.
-POSIX requires that CLOCKS_PER_SEC equals 1000000 independent
+be represented, the function returns the value
+.IR (clock_t)\ \-1 .
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lb lb lb
+l l l.
+Interface      Attribute       Value
+T{
+.BR clock ()
+T}     Thread safety   MT-Safe
+.TE
+.sp 1
+.SH CONFORMING TO
+POSIX.1-2001, POSIX.1-2008, C89, C99.
+XSI requires that
+.B CLOCKS_PER_SEC
+equals 1000000 independent
 of the actual resolution.
 .SH NOTES
 The C standard allows for arbitrary values at the start of the program;
@@ -55,8 +73,9 @@ subtract the value returned from a call to
 at the start of the program to get maximum portability.
 .PP
 Note that the time can wrap around.
-On a 32bit system where
-CLOCKS_PER_SEC equals 1000000 this function will return the same
+On a 32-bit system where
+.B CLOCKS_PER_SEC
+equals 1000000 this function will return the same
 value approximately every 72 minutes.
 .PP
 On several other implementations,
@@ -69,7 +88,7 @@ collected via
 Linux does not include the times of waited-for children in the
 value returned by
 .BR clock ().
-.\" I have seen this behaviour on Irix 6.3, and the OSF/1, HP/UX, and
+.\" I have seen this behavior on Irix 6.3, and the OSF/1, HP/UX, and
 .\" Solaris manual pages say that clock() also does this on those systems.
 .\" POSIX.1-2001 doesn't explicitly allow this, nor is there an
 .\" explicit prohibition. -- MTK
@@ -77,6 +96,18 @@ The
 .BR times (2)
 function, which explicitly returns (separate) information about the
 caller and its children, may be preferable.
-.SH "SEE ALSO"
+.PP
+In glibc 2.17 and earlier,
+.BR clock ()
+was implemented on top of
+.BR times (2).
+For improved accuracy,
+since glibc 2.18, it is implemented on top of
+.BR clock_gettime (2)
+(using the
+.BR CLOCK_PROCESS_CPUTIME_ID
+clock).
+.SH SEE ALSO
+.BR clock_gettime (2),
 .BR getrusage (2),
 .BR times (2)