Tcl_DoWhenIdle(3) Tcl Library Procedures Tcl_DoWhenIdle(3)
Tcl_DoWhenIdle, Tcl_CancelIdleCall - invoke a procedure when there are
no pending events
Tcl_IdleProc *proc (in) Procedure to invoke.
ClientData clientData (in) Arbitrary one-word value to pass
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, couldn't 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
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's 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 bet-
ter to use a timer handler with a zero timeout period.
callback, defer, idle callback
Tcl 7.5 Tcl_DoWhenIdle(3)