NAME
       vwait - Process events until a variable is written

SYNOPSIS
       vwait varName


DESCRIPTION
       This  command enters the Tcl event loop to process events,
       blocking the application if no events are ready.  It  con-
       tinues processing events until some event handler sets the
       value of variable varName.  Once varName has been set, the
       vwait  command  will  return  as soon as the event handler
       that modified varName completes.

       In some cases the vwait command may not return immediately
       after  varName  is set.  This can happen if the event han-
       dler that sets varName does not complete immediately.  For
       example,  if an event handler sets varName and then itself
       calls vwait to wait for a different variable, then it  may
       not  return  for  a  long time.  During this time the top-
       level vwait is blocked waiting for the  event  handler  to
       complete, so it cannot return either.


KEYWORDS
       event, variable, wait
