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
       continues  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.   varName  must  globally
       scoped  (either  with a call to global for the varName, or
       with the full namespace path specification).

       In some cases the vwait command may not return immediately
       after  varName  is  set.   This  can  happen  if the event
       handler 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
