fcopy.n

linux系统下的音频通信

'\"
'\" Copyright (c) 1993 The Regents of the University of California.
'\" Copyright (c) 1994-1997 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\" 
'\" SCCS: @(#) fcopy.n 1.4 97/06/19 11:10:07
'\" 
.so man.macros
.TH fcopy n 8.0 Tcl "Tcl Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
fcopy \- Copy data from one channel to another.
.SH SYNOPSIS
\fBfcopy \fIinchan\fR \fIoutchan\fR ?\fB\-size \fIsize\fR? ?\fB\-command \fIcallback\fR?
.BE

.SH DESCRIPTION
.PP
The \fBfcopy\fP command copies data from one I/O channel, \fIinchan\fR to another I/O channel, \fIoutchan\fR.
The \fBfcopy\fP command leverages the buffering in the Tcl I/O system to
avoid extra copies and to avoid buffering too much data in
main memory when copying large files to slow destinations like
network sockets.
.PP
The \fBfcopy\fP 
command transfers data from \fIinchan\fR until end of file
or \fIsize\fP bytes have been 
transferred. If no \fB\-size\fP argument is given,
then the copy goes until end of file.
All the data read from \fIinchan\fR is copied to \fIoutchan\fR.
Without the \fB\-command\fP option, \fBfcopy\fP blocks until the copy is complete
and returns the number of bytes written to \fIoutchan\fR.
.PP
The \fB\-command\fP argument makes \fBfcopy\fP work in the background.
In this case it returns immediately and the \fIcallback\fP is invoked
later when the copy completes.
The \fIcallback\fP is called with
one or two additional 
arguments that indicates how many bytes were written to \fIoutchan\fR.
If an error occurred during the background copy, the second argument is the
error string associated with the error.
With a background copy,
it is not necessary to put \fIinchan\fR or \fIoutchan\fR into
non-blocking mode; the \fBfcopy\fP command takes care of that automatically.
However, it is necessary to enter the event loop by using
the \fBvwait\fP command or by using Tk.
.PP
You are not allowed to do other I/O operations with
\fIinchan\fR or \fIoutchan\fR during a background fcopy.
If either \fIinchan\fR or \fIoutchan\fR get closed
while the copy is in progress, the current copy is stopped
and the command callback is \fInot\fP made.
If \fIinchan\fR is closed,
then all data already queued for \fIoutchan\fR is written out.
.PP
Note that \fIinchan\fR can become readable during a background copy.
You should turn off any \fBfileevent\fP handlers during a background
copy so those handlers do not interfere with the copy.
Any I/O attempted by a \fBfileevent\fP handler will get a "channel busy" error.
.PP
\fBFcopy\fR translates end-of-line sequences in \fIinchan\fR and \fIoutchan\fR
according to the \fB\-translation\fR option
for these channels.
See the manual entry for \fBfconfigure\fR for details on the
\fB\-translation\fR option.
The translations mean that the number of bytes read from \fIinchan\fR
can be different than the number of bytes written to \fIoutchan\fR.
Only the number of bytes written to \fIoutchan\fR is reported,
either as the return value of a synchronous \fBfcopy\fP or
as the argument to the callback for an asynchronous \fBfcopy\fP.

.SH EXAMPLE
.PP
This first example shows how the callback gets
passed the number of bytes transferred.
It also uses vwait to put the application into the event loop.
Of course, this simplified example could be done without the command 
callback.
.DS
proc Cleanup {in out bytes {error {}}} {
    global total
    set total $bytes
    close $in
    close $out
    if {[string length $error] != 0} {
	# error occurred during the copy
    }
}
set in [open $file1]
set out [socket $server $port]
fcopy $in $out -command [list Cleanup $in $out]
vwait total

.DE
.PP
The second example copies in chunks and tests for end of file
in the command callback
.DS
proc CopyMore {in out chunk bytes {error {}}} {
    global total done
    incr total $bytes
    if {([string length $error] != 0) || [eof $in] {
	set done $total
	close $in
	close $out
    } else {
	fcopy $in $out -command [list CopyMore $in $out $chunk] \\
	    -size $chunk
    }
}
set in [open $file1]
set out [socket $server $port]
set chunk 1024
set total 0
fcopy $in $out -command [list CopyMore $in $out $chunk] -size $chunk
vwait done

.DE

.SH "SEE ALSO"
eof(n), fblocked(n), fconfigure(n)

.SH KEYWORDS
blocking, channel, end of line, end of file, nonblocking, read, translation