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
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.
typedef void Tcl_IdleProc(ClientData clientData);
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.