Tribblix: manual page: Tcl

Tcl_GetTime(3) Tcl Library Procedures Tcl_GetTime(3)

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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
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.
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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
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.

KEYWORDS