plucky (3) fifo.3tcl.gz

NAME

       fifo - Create and manipulate u-turn fifo channels

SYNOPSIS

       package require Tcl

       package require memchan

       fifo

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DESCRIPTION

       fifo   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

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

       -allocated
              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>