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fifo(3tcl) fifo(3tcl) 





NAME


fifo - Create and manipulate u-turn fifo channels






SYNOPSIS


package require Tcl 


package require memchan 


fifo










DESCRIPTION



  

  
creates a stream-oriented in-memory channel and returns its handle. There
      is no restriction on the ultimate size of the channel, it will always grow
      as much as is necessary to accommodate the data written into it.
    
In contrast to the channels generated by memchan a
        channel created here effectively represents an U-turn. All data written
        into it can be read out, but only in the same order. This also means
        that a fifo channel is not seekable.

    
The channels created here can be transferred between
        interpreters in the same thread and between threads, but only as a
        whole. It is not possible to use them to create a bi- or unidirectional
        connection between two interpreters.

  




Memory channels created by fifo provide two read-only
    options which can be queried via the standard fconfigure command.
    These are



  

  
The value of this option is the number of bytes currently stored in the
      queried memory channel.

  

  
The value of this option is the number of bytes currently allocated by the
      queried memory channel. This number is at least as big as the value of
      -length.




As the channels generated by fifo grow as necessary they
    are always writable. This means that a writable fileevent-handler
    will fire continuously.


The channels are also readable if they contain more than zero
    bytes. Under this conditions a readable fileevent-handler will fire
    continuously.






NOTES


One possible application of memory channels created by
    memchan or fifo is as temporary storage device to collect data
    coming in over a pipe or a socket. If part of the processing of the incoming
    data is to read and process header bytes or similar fifo are easier to use
    as they do not require seeking back and forth to switch between the
    assimilation of headers at the beginning and writing new data at the
  end.






SEE ALSO


fifo2, memchan, null






KEYWORDS


channel, fifo, i/o, in-memory channel, memchan, stream






COPYRIGHT


Copyright (c) 1996-2003 Andreas Kupries <andreas_kupries@users.sourceforge.net>








  

    2.1
    Memory channels