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(3tcl), update(3tcl)

KEYWORDS

       event, variable, wait