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

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NAME

       vwait - Process events until a variable is written

SYNOPSIS

       vwait varName
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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 complete,  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 running 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)