93 lines
3.7 KiB
Groff
93 lines
3.7 KiB
Groff
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'\"
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'\" Copyright (c) 1996 Sun Microsystems, Inc.
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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'\" SCCS: @(#) CrtChnlHdlr.3 1.10 96/03/14 10:54:43
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.so man.macros
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.TH Tcl_CreateChannelHandler 3 7.5 Tcl "Tcl Library Procedures"
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.BS
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'\" Note: do not modify the .SH NAME line immediately below!
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.SH NAME
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Tcl_CreateChannelHandler, Tcl_DeleteChannelHandler \- call a procedure when a channel becomes readable or writable
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.SH SYNOPSIS
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.nf
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.nf
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\fB#include <tcl.h>\fR
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.sp
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void
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\fBTcl_CreateChannelHandler\fR(\fIchannel, mask, proc, clientData\fR)
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.sp
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void
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\fBTcl_DeleteChannelHandler\fR(\fIchannel, proc, clientData\fR)
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.sp
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.SH ARGUMENTS
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.AS Tcl_ChannelProc clientData
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.AP Tcl_Channel channel in
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Tcl channel such as returned by \fBTcl_CreateChannel\fR.
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.AP int mask in
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Conditions under which \fIproc\fR should be called: OR-ed combination of
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\fBTCL_READABLE\fR, \fBTCL_WRITABLE\fR and \fBTCL_EXCEPTION\fR. Specify
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a zero value to temporarily disable an existing handler.
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.AP Tcl_FileProc *proc in
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Procedure to invoke whenever the channel indicated by \fIchannel\fR meets
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the conditions specified by \fImask\fR.
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.AP ClientData clientData in
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Arbitrary one-word value to pass to \fIproc\fR.
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.BE
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.SH DESCRIPTION
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.PP
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\fBTcl_CreateChannelHandler\fR arranges for \fIproc\fR to be called in the
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future whenever input or output becomes possible on the channel identified
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by \fIchannel\fR, or whenever an exceptional condition exists for
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\fIchannel\fR. The conditions of interest under which \fIproc\fR will be
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invoked are specified by the \fImask\fR argument.
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See the manual entry for \fBfileevent\fR for a precise description of
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what it means for a channel to be readable or writable.
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\fIProc\fR must conform to the following prototype:
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.CS
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typedef void Tcl_ChannelProc(
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ClientData \fIclientData\fR,
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int \fImask\fR);
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.CE
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.PP
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The \fIclientData\fR argument is the same as the value passed to
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\fBTcl_CreateChannelHandler\fR when the handler was created. Typically,
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\fIclientData\fR points to a data structure containing application-specific
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information about the channel. \fIMask\fR is an integer mask indicating
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which of the requested conditions actually exists for the channel; it will
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contain a subset of the bits from the \fImask\fR argument to
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\fBTcl_CreateChannelHandler\fR when the handler was created.
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.PP
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Each channel handler is identified by a unique combination of \fIchannel\fR,
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\fIproc\fR and \fIclientData\fR.
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There may be many handlers for a given channel as long as they don't
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have the same \fIchannel\fR, \fIproc\fR, and \fIclientData\fR.
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If \fBTcl_CreateChannelHandler\fR is invoked when there is already a handler
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for \fIchannel\fR, \fIproc\fR, and \fIclientData\fR, then no new
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handler is created; instead, the \fImask\fR is changed for the
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existing handler.
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.PP
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\fBTcl_DeleteChannelHandler\fR deletes a channel handler identified by
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\fIchannel\fR, \fIproc\fR and \fIclientData\fR; if no such handler exists,
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the call has no effect.
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.PP
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Channel handlers are invoked via the Tcl event mechanism, so they
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are only useful in applications that are event-driven.
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Note also that the conditions specified in the \fImask\fR argument
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to \fIproc\fR may no longer exist when \fIproc\fR is invoked: for
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example, if there are two handlers for \fBTCL_READABLE\fR on the same
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channel, the first handler could consume all of the available input
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so that the channel is no longer readable when the second handler
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is invoked.
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For this reason it may be useful to use nonblocking I/O on channels
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for which there are event handlers.
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.SH "SEE ALSO"
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Notifier(3), Tcl_CreateChannel(3), Tcl_OpenFileChannel(3), vwait(n).
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.SH KEYWORDS
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blocking, callback, channel, events, handler, nonblocking.
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