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man pages section 3: Extended Library Functions, Volume 1

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Updated: Wednesday, July 27, 2022
 
 

Tcl_DoWhenIdle (3tcl)

Name

Tcl_DoWhenIdle - invoke a procedure when there are no pending events

Synopsis

#include <tcl.h>

Tcl_DoWhenIdle(proc, clientData)

Tcl_CancelIdleCall(proc, clientData)

Description

Tcl_DoWhenIdle(3tcl)        Tcl Library Procedures        Tcl_DoWhenIdle(3tcl)



______________________________________________________________________________

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.
______________________________________________________________________________

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 struc-
       ture 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 bet-
       ter to use a timer handler with a zero timeout period.


ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       +---------------+------------------+
       |ATTRIBUTE TYPE | ATTRIBUTE VALUE  |
       +---------------+------------------+
       |Availability   | runtime/tcl-8    |
       +---------------+------------------+
       |Stability      | Uncommitted      |
       +---------------+------------------+

SEE ALSO
       after(n), Tcl_CreateFileHandler(3), Tcl_CreateTimerHandler(3)

KEYWORDS
       callback, defer, idle callback



NOTES
       Source  code  for open source software components in Oracle Solaris can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-
       code-downloads.html.

       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source was downloaded from  http://prdownloads.sourceforge.net/tcl/tcl-
       core8.6.7-src.tar.gz.

       Further information about this software can be found on the open source
       community website at https://www.tcl.tk/.



Tcl                                   7.5                 Tcl_DoWhenIdle(3tcl)