diff options
Diffstat (limited to 'doc/close.n')
| -rw-r--r-- | doc/close.n | 20 |
1 files changed, 15 insertions, 5 deletions
diff --git a/doc/close.n b/doc/close.n index 800ee8a..c4b1612 100644 --- a/doc/close.n +++ b/doc/close.n @@ -5,7 +5,7 @@ '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" -'\" RCS: @(#) $Id: close.n,v 1.14 2008/10/17 10:22:25 dkf Exp $ +'\" RCS: @(#) $Id: close.n,v 1.15 2008/12/18 01:14:16 ferrieux Exp $ '\" .so man.macros .TH close n 7.5 Tcl "Tcl Built-In Commands" @@ -14,19 +14,20 @@ .SH NAME close \- Close an open channel .SH SYNOPSIS -\fBclose \fIchannelId\fR +\fBclose \fIchannelId\fR ?r(ead)|w(rite)? .BE .SH DESCRIPTION .PP -Closes the channel given by \fIchannelId\fR. +Closes or half-closes the channel given by \fIchannelId\fR. .PP \fIChannelId\fR must be an identifier for an open channel such as a Tcl standard channel (\fBstdin\fR, \fBstdout\fR, or \fBstderr\fR), the return value from an invocation of \fBopen\fR or \fBsocket\fR, or the result of a channel creation command provided by a Tcl extension. .PP -All buffered output is flushed to the channel's output device, +The single-argument form is a simple "full-close": +all buffered output is flushed to the channel's output device, any buffered input is discarded, the underlying file or device is closed, and \fIchannelId\fR becomes unavailable for use. .PP @@ -56,6 +57,15 @@ The command returns an empty string, and may generate an error if an error occurs while flushing output. If a command in a command pipeline created with \fBopen\fR returns an error, \fBclose\fR generates an error (similar to the \fBexec\fR command.) +.PP +The two-argument form is a "half-close": given a bidirectional channel like a socket or command pipeline and a (possibly abbreviated) direction, it closes only the substream going in that direction. This means a shutdown() on a socket, and a close() of one end of a pipe for a command pipeline. Then, the Tcl-level channel data structure is either kept or freed depending on whether the other direction is still open. +.PP +A single-argument close on an already half-closed bi-channel is defined to just "finish the job. A half-close on an already closed half, or on a wrong-sided unidirectional channel, raises an error. +.PP +In the case of a command pipeline, the child-reaping duty falls upon the shoulders of the last close or half-close, which is thus allowed to report an abnormal exit error. +.PP +Currently only sockets and command pipelines support half-close. A future extension will allow reflected and stacked channels to do so. + .SH EXAMPLE .PP This illustrates how you can use Tcl to ensure that files get closed @@ -76,4 +86,4 @@ proc withOpenFile {filename channelVar script} { .SH "SEE ALSO" file(n), open(n), socket(n), eof(n), Tcl_StandardChannels(3) .SH KEYWORDS -blocking, channel, close, nonblocking +blocking, channel, close, nonblocking, half-close |