fifo(3tcl)                                                                                                                              fifo(3tcl)

NAME

       fifo - Create and manipulate u-turn fifo channels

SYNOPSIS

       package require Tcl

       package require memchan

       fifo

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 con-
       tinuously.

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

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>

Memory channels                                                         2.1                                                             fifo(3tcl)