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vwait(n)                                    Tcl Built-In Commands                                   vwait(n)



____________________________________________________________________________________________________________

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 be 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  com-plete, complete,
       plete, so it cannot return either.

EXAMPLES
       Run  the event-loop continually until some event calls exit.  (You can use any variable not mentioned
       elsewhere, but the name forever reminds you at a glance of the intent.)
              vwait forever

       Wait five seconds for a connection to a server socket, otherwise close the socket and  continue  run-ning running
       ning the script:
              # Initialise the state
              after 5000 set state timeout
              set server [socket -server accept 12345]
              proc accept {args} {
                 global state connectionInfo
                 set state accepted
                 set connectionInfo $args
              }

              # Wait for something to happen
              vwait state

              # Clean up events that could have happened
              close $server
              after cancel set state timeout

              # Do something based on how the vwait finished...
              switch $state {
                 timeout {
                    puts "no connection on port 12345"
                 }
                 accepted {
                    puts "connection: $connectionInfo"
                    puts [lindex $connectionInfo 0] "Hello there!"
                 }
              }


SEE ALSO
       global(n), update(n)


KEYWORDS
       event, variable, wait



Tcl                                                  8.0                                            vwait(n)