| Allegro CL version 8.2 Unrevised from 8.1 to 8.2. 8.1 version |
Arguments: stream
In brief, if the argument stream is an integer,
read-no-hang-p views that
integer as an output file-descriptor, and it just checks the
file-descriptor for readiness. If stream is a
stream, its input-handle is queried to see if reading can be
done. True is returned if reading can be done, else nil
is returned. If the handle is itself a stream (an
encapsulation), the stream is examined in a way similar to a listen,
but an eof or an error situation always causes a return of true.
The actual implementation is more complicated and probably of interest only to strategy-level programmers. See Simple-stream Description in streams.htm for a discussion of different sorts of programmers.
If stream is a dual-channel stream that has the
record-end set to -1, read-no-hang-p will call device-finish-record with
:listen
as the value of the
blocking argument and
:prime-input
as the value of the
action, and return nil if that call returns
nil
, or t
if that
call returns :eof
.
For other stream types, the buffer is checked for emptiness. If it is
not empty, t
is returned (after a possible
record-end check - see below).
If the buffer is empty, then device-read is called with a
blocking argument of nil
. Any eof or error condition will result in
t
being returned, and if no octets were read
otherwise, nil
is returned.
If stream is a dual-channel stream with
record-end set, and if the read was able to get some data, or if the
buffer was not empty to start with, the the record end is checked. If
the record has ended, then device-finish-record is called with null
blocking argument and action
:input
, and if it returns nil
, nil
is returned.
Otherwise, t
is returned.
See streams.htm for information on the simple-streams implementation in Allegro CL.
Copyright (c) 1998-2016, Franz Inc. Oakland, CA., USA. All rights reserved.
This page was not revised from the 8.1 page.
Created 2010.1.21.
| Allegro CL version 8.2 Unrevised from 8.1 to 8.2. 8.1 version |