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Diffstat (limited to 'doc/close.n')
| -rw-r--r-- | doc/close.n | 38 |
1 files changed, 31 insertions, 7 deletions
diff --git a/doc/close.n b/doc/close.n index 4ef3c7d..2577cc5 100644 --- a/doc/close.n +++ b/doc/close.n @@ -12,19 +12,19 @@ .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 @@ -54,10 +54,32 @@ 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 +.VS 8.6 +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. +.VE 8.6 .SH EXAMPLE +.PP This illustrates how you can use Tcl to ensure that files get closed even when errors happen by combining \fBcatch\fR, \fBclose\fR and \fBreturn\fR: +.PP .CS proc withOpenFile {filename channelVar script} { upvar 1 $channelVar chan @@ -69,9 +91,11 @@ proc withOpenFile {filename channelVar script} { return -options $options $result } .CE - .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 +'\" Local Variables: +'\" mode: nroff +'\" fill-column: 78 +'\" End: |