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
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>