Ubuntu Manpage: fifo - Create and manipulate u-turn fifo channels

Provided by: tcl-memchan_2.3+dfsg-1build1_amd64

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.

KEYWORDS

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

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