Tcl/Tk Documentation > TclLib > DoWhenIdle
- Tcl_IdleProc *proc (in)
- Procedure to invoke.
- ClientData clientData (in)
- Arbitrary one-word value to pass to proc.
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.callback, defer, idle callback