oasis-root

times.3p (6049B)

'\" et
.TH TIMES "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
times
\(em get process and waited-for child process times
.SH SYNOPSIS
.LP
.nf
#include <sys/times.h>
.P
clock_t times(struct tms *\fIbuffer\fP);
.fi
.SH DESCRIPTION
The
\fItimes\fR()
function shall fill the
.BR tms
structure pointed to by
.IR buffer
with time-accounting information. The
.BR tms
structure is defined in
.IR <sys/times.h> .
.P
All times are measured in terms of the number of clock ticks used.
.P
The times of a terminated child process shall be included in the
.IR tms_cutime
and
.IR tms_cstime
elements of the parent when
\fIwait\fR(),
\fIwaitid\fR(),
or
\fIwaitpid\fR()
returns the process ID of this terminated child. If a child process
has not waited for its children, their times shall not be included in
its times.
.IP " *" 4
The
.IR tms_utime
structure member is the CPU time charged for the execution of user
instructions of the calling process.
.IP " *" 4
The
.IR tms_stime
structure member is the CPU time charged for execution by the system on
behalf of the calling process.
.IP " *" 4
The
.IR tms_cutime
structure member is the sum of the
.IR tms_utime
and
.IR tms_cutime
times of the child processes.
.IP " *" 4
The
.IR tms_cstime
structure member is the sum of the
.IR tms_stime
and
.IR tms_cstime
times of the child processes.
.SH "RETURN VALUE"
Upon successful completion,
\fItimes\fR()
shall return the elapsed real time, in clock ticks, since an arbitrary
point in the past (for example, system start-up time). This point does
not change from one invocation of
\fItimes\fR()
within the process to another. The return value may overflow the
possible range of type
.BR clock_t .
If
\fItimes\fR()
fails, (\fBclock_t\fR)\-1 shall be returned and
.IR errno
set to indicate the error.
.SH ERRORS
The
\fItimes\fR()
function shall fail if:
.TP
.BR EOVERFLOW
The return value would overflow the range of
.BR clock_t .
.LP
.IR "The following sections are informative."
.SH EXAMPLES
.SS "Timing a Database Lookup"
.P
The following example defines two functions,
\fIstart_clock\fR()
and
\fIend_clock\fR(),
that are used to time a lookup. It also defines variables of type
.BR clock_t
and
.BR tms
to measure the duration of transactions. The
\fIstart_clock\fR()
function saves the beginning times given by the
\fItimes\fR()
function. The
\fIend_clock\fR()
function gets the ending times and prints the difference between the
two times.
.sp
.RS 4
.nf
#include <sys/times.h>
#include <stdio.h>
\&...
void start_clock(void);
void end_clock(char *msg);
\&...
static clock_t st_time;
static clock_t en_time;
static struct tms st_cpu;
static struct tms en_cpu;
\&...
void
start_clock()
{
    st_time = times(&st_cpu);
}
.P
/* This example assumes that the result of each subtraction
   is within the range of values that can be represented in
   an integer type. */
void
end_clock(char *msg)
{
    en_time = times(&en_cpu);
.P
    fputs(msg,stdout);
    printf("Real Time: %jd, User Time %jd, System Time %jd\en",
        (intmax_t)(en_time - st_time),
        (intmax_t)(en_cpu.tms_utime - st_cpu.tms_utime),
        (intmax_t)(en_cpu.tms_stime - st_cpu.tms_stime));
}
.fi
.P
.RE
.SH "APPLICATION USAGE"
Applications should use \fIsysconf\fP(_SC_CLK_TCK)
to determine the number of clock ticks per second as it may vary from
system to system.
.SH RATIONALE
The accuracy of the times reported is intentionally left unspecified to
allow implementations flexibility in design, from uniprocessor to
multi-processor networks.
.P
The inclusion of times of child processes is recursive, so that a
parent process may collect the total times of all of its descendants.
But the times of a child are only added to those of its parent when its
parent successfully waits on the child. Thus, it is not guaranteed
that a parent process can always see the total times of all its
descendants; see also the discussion of the term ``realtime'' in
.IR "\fIalarm\fR\^(\|)".
.P
If the type
.BR clock_t
is defined to be a signed 32-bit integer, it overflows in somewhat more
than a year if there are 60 clock ticks per second,
or less than a year if there are 100. There are individual systems
that run continuously for longer than that. This volume of POSIX.1\(hy2017 permits an
implementation to make the reference point for the returned value be
the start-up time of the process, rather than system start-up time.
.P
The term ``charge'' in this context has nothing to do with billing
for services. The operating system accounts for time used in this
way. That information must be correct, regardless of how that
information is used.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIalarm\fR\^(\|)",
.IR "\fIexec\fR\^",
.IR "\fIfork\fR\^(\|)",
.IR "\fIsysconf\fR\^(\|)",
.IR "\fItime\fR\^(\|)",
.IR "\fIwait\fR\^(\|)",
.IR "\fIwaitid\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<sys_times.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .