- 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
- DESCRIPTION
- BUGS
- SEE
ALSO
- KEYWORDS
Tcl_DoWhenIdle, Tcl_CancelIdleCall — invoke a procedure when there
are no pending events
#include <tcl.h>
Tcl_DoWhenIdle(proc, clientData)
Tcl_CancelIdleCall(proc, clientData)
- Tcl_IdleProc *proc (in)
- Procedure to invoke.
- ClientData clientData (in)
- Arbitrary one-word value to pass to proc.
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.
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.
after, Tcl_CreateFileHandler,
Tcl_CreateTimerHandler
callback, defer, idle callback
Copyright © 1990 The Regents of the University of
California.
Copyright © 1994-1996 Sun Microsystems, Inc.