Tcl_DoWhenIdle(3) Tcl Library Procedures Tcl_DoWhenIdle(3)
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NAME
Tcl_DoWhenIdle, Tcl_CancelIdleCall - invoke a procedure when there
are no pending events
SYNOPSIS
#include <tcl.h> Tcl_DoWhenIdle(
proc, clientData)
Tcl_CancelIdleCall(
proc, clientData)
ARGUMENTS
Tcl_IdleProc
*proc (in) Procedure to invoke.
ClientData
clientData (in) Arbitrary one-word value to
pass to
proc.
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DESCRIPTION
Tcl_DoWhenIdle arranges for
proc to be invoked when the application
becomes idle. The application is considered to be idle when
Tcl_DoOneEvent has been called, could not find any events to handle,
and is about to go to sleep waiting for an event to occur. At this
point all pending
Tcl_DoWhenIdle handlers are invoked. For each call
to
Tcl_DoWhenIdle there will be a single call to
proc; after
proc is
invoked the handler is automatically removed.
Tcl_DoWhenIdle is only
usable in programs that use
Tcl_DoOneEvent to dispatch events.
Proc should have arguments and result that match the type
Tcl_IdleProc:
typedef void
Tcl_IdleProc(
ClientData
clientData);
The
clientData parameter to
proc is a copy of the
clientData argument
given to
Tcl_DoWhenIdle. Typically,
clientData points to a data
structure containing application-specific information about what
proc should do.
Tcl_CancelIdleCall may be used to cancel one or more previous calls
to
Tcl_DoWhenIdle: if there is a
Tcl_DoWhenIdle handler registered
for
proc and
clientData, then it is removed without invoking it. If
there is more than one handler on the idle list that refers to
proc and
clientData, all of the handlers are removed. If no existing
handlers match
proc and
clientData then nothing happens.
Tcl_DoWhenIdle is most useful in situations where (a) a piece of work
will have to be done but (b) it is possible that something will
happen in the near future that will change what has to be done or
require something different to be done.
Tcl_DoWhenIdle allows the
actual work to be deferred until all pending events have been
processed. At this point the exact work to be done will presumably
be known and it can be done exactly once.
For example,
Tcl_DoWhenIdle might be used by an editor to defer
display updates until all pending commands have been processed.
Without this feature, redundant redisplays might occur in some
situations, such as the processing of a command file.
BUGS
At present it is not safe for an idle callback to reschedule itself
continuously. This will interact badly with certain features of Tk
that attempt to wait for all idle callbacks to complete. If you
would like for an idle callback to reschedule itself continuously, it
is better to use a timer handler with a zero timeout period.
SEE ALSO
after(n),
Tcl_CreateFileHandler(3),
Tcl_CreateTimerHandler(3)KEYWORDS
callback, defer, idle callback
Tcl 7.5 Tcl_DoWhenIdle(3)
