Tcl_GetTime(3tcl) Tcl Library Procedures Tcl_GetTime(3tcl)
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NAME
Tcl_GetTime, Tcl_SetTimeProc, Tcl_QueryTimeProc - get date and time
SYNOPSIS
#include <tcl.h>
Tcl_GetTime(timePtr)
Tcl_SetTimeProc(getProc, scaleProc, clientData)
Tcl_QueryTimeProc(getProcPtr, scaleProcPtr, clientDataPtr)
ARGUMENTS
Tcl_Time *timePtr (out) Points to memory in which to
store the date and time informa-
tion.
Tcl_GetTimeProc getProc (in) Pointer to handler function re-
placing Tcl_GetTime's access to
the OS.
Tcl_ScaleTimeProc scaleProc (in) Pointer to handler function for
the conversion of time delays in
the virtual domain to real-time.
ClientData clientData (in) Value passed through to the two
handler functions.
Tcl_GetTimeProc *getProcPtr (out) Pointer to place the currently
registered get handler function
into.
Tcl_ScaleTimeProc *scaleProcPtr (out) Pointer to place the currently
registered scale handler func-
tion into.
ClientData *clientDataPtr (out) Pointer to place the currently
registered pass-through value
into.
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DESCRIPTION
The Tcl_GetTime function retrieves the current time as a Tcl_Time
structure in memory the caller provides. This structure has the fol-
lowing definition:
typedef struct Tcl_Time {
long sec;
long usec;
} Tcl_Time;
On return, the sec member of the structure is filled in with the number
of seconds that have elapsed since the epoch: the epoch is the point in
time of 00:00 UTC, 1 January 1970. This number does not count leap
seconds - an interval of one day advances it by 86400 seconds regard-
less of whether a leap second has been inserted.
The usec member of the structure is filled in with the number of mi-
croseconds that have elapsed since the start of the second designated
by sec. The Tcl library makes every effort to keep this number as pre-
cise 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 usec field is derived from a performance counter
and is highly precise.)
VIRTUALIZED TIME
The Tcl_SetTimeProc function registers two related handler functions
with the core. The first handler function is a replacement for Tcl_Get-
Time, or rather the OS access made by Tcl_GetTime. The other handler
function is used by the Tcl notifier to convert wait/block times from
the virtual domain into real time.
The Tcl_QueryTimeProc 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.
The signatures of the handler functions are as follows:
typedef void Tcl_GetTimeProc(
Tcl_Time *timebuf,
ClientData clientData);
typedef void Tcl_ScaleTimeProc(
Tcl_Time *timebuf,
ClientData clientData);
The timebuf fields contain the time to manipulate, and the clientData
fields contain a pointer supplied at the time the handler functions
were registered.
Any handler pair specified has to return data which is consistent be-
tween them. In other words, setting one handler of the pair to some-
thing assuming a 10-times slowdown, and the other handler of the pair
to something assuming a two-times slowdown is wrong and not allowed.
The set handler functions are allowed to run the delivered time back-
wards, however this should be avoided. We have to allow it as the na-
tive 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.
SEE ALSO
clock(3tcl)
KEYWORDS
date, time
Tcl 8.4 Tcl_GetTime(3tcl)
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