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 information.
- Tcl_GetTimeProc getProc (in)
- Pointer to handler function replacing 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 function
into.
- ClientData *clientDataPtr (out)
- Pointer to place the currently registered pass-through value into.
DESCRIPTION¶
The
Tcl_GetTime function retrieves the current time as a
Tcl_Time
structure in memory the caller provides. This structure has the following
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 regardless of
whether a leap second has been inserted.
The
usec member of the structure is filled in with the number of
microseconds that have elapsed since the start of the second designated by
sec. 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
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_GetTime,
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 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.
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.
SEE ALSO¶
clock(3tcl)
KEYWORDS¶
date, time