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'\"
'\" Copyright (c) 2001 Kevin B. Kenny <kennykb@acm.org>.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH Tcl_GetTime 3 8.4 Tcl "Tcl Library Procedures"
.so man.macros
.BS
.SH NAME
Tcl_GetTime, Tcl_SetTimeProc, Tcl_QueryTimeProc \- get date and time
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
\fBTcl_GetTime\fR(\fItimePtr\fR)
.sp
\fBTcl_SetTimeProc\fR(\fIgetProc, scaleProc, clientData\fR)
.sp
\fBTcl_QueryTimeProc\fR(\fIgetProcPtr, scaleProcPtr, clientDataPtr\fR)
.fi
.SH ARGUMENTS
.AS Tcl_GetTimeProc *getProc in
.AP Tcl_Time *timePtr out
Points to memory in which to store the date and time information.
.AP Tcl_GetTimeProc getProc in
Pointer to handler function replacing \fBTcl_GetTime\fR's access to the OS.
.AP Tcl_ScaleTimeProc scaleProc in
Pointer to handler function for the conversion of time delays in the
virtual domain to real-time.
.AP void *clientData in
Value passed through to the two handler functions.
.AP Tcl_GetTimeProc *getProcPtr out
Pointer to place the currently registered get handler function into.
.AP Tcl_ScaleTimeProc *scaleProcPtr out
Pointer to place the currently registered scale handler function into.
.AP void **clientDataPtr out
Pointer to place the currently registered pass-through value into.
.BE
.SH DESCRIPTION
.PP
The \fBTcl_GetTime\fR function retrieves the current time as a
\fITcl_Time\fR structure in memory the caller provides. This
structure has the following definition:
.PP
.CS
typedef struct {
long long \fIsec\fR;
long \fIusec\fR;
} \fBTcl_Time\fR;
.CE
.PP
On return, the \fIsec\fR member of the structure is filled in with the
number of seconds that have elapsed since the \fIepoch:\fR the epoch
is the point in time of 00:00 UTC, 1 January 1970. This number does
\fInot\fR count leap seconds; an interval of one day advances it by
86400 seconds regardless of whether a leap second has been inserted.
.PP
The \fIusec\fR member of the structure is filled in with the number of
microseconds that have elapsed since the start of the second
designated by \fIsec\fR. The Tcl library makes every effort to keep
this number as precise as possible, subject to the limitations of the
computer system. On multiprocessor variants of Windows, this number
may be limited to the 10- or 20-ms granularity of the system clock.
(On single-processor Windows systems, the \fIusec\fR field is derived
from a performance counter and is highly precise.)
.SS "VIRTUALIZED TIME"
.PP
The \fBTcl_SetTimeProc\fR function registers two related handler functions
with the core. The first handler function is a replacement for
\fBTcl_GetTime\fR, or rather the OS access made by
\fBTcl_GetTime\fR. The other handler function is used by the Tcl
notifier to convert wait/block times from the virtual domain into real
time.
.PP
The \fBTcl_QueryTimeProc\fR function returns the currently registered
handler functions. If no external handlers were set then this will
return the standard handlers accessing and processing the native time
of the OS. The arguments to the function are allowed to be NULL; and
any argument which is NULL is ignored and not set.
.PP
The signatures of the handler functions are as follows:
.PP
.CS
typedef void \fBTcl_GetTimeProc\fR(
Tcl_Time *\fItimebuf\fR,
void *\fIclientData\fR);
typedef void \fBTcl_ScaleTimeProc\fR(
Tcl_Time *\fItimebuf\fR,
void *\fIclientData\fR);
.CE
.PP
The \fItimebuf\fR fields contain the time to manipulate, and the
\fIclientData\fR fields contain a pointer supplied at the time the handler
functions were registered.
.PP
Any handler pair specified has to return data which is consistent between
them. In other words, setting one handler of the pair to something assuming a
10-times slowdown, and the other handler of the pair to something assuming a
two-times slowdown is wrong and not allowed.
.PP
The set handler functions are allowed to run the delivered time backwards,
however this should be avoided. We have to allow it as the native time can run
backwards as the user can fiddle with the system time one way or other. Note
that the insertion of the hooks will not change the behavior of the Tcl core
with regard to this situation, i.e. the existing behavior is retained.
.SH "SEE ALSO"
clock(n)
.SH KEYWORDS
date, time
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