111 lines
4.3 KiB
Groff
111 lines
4.3 KiB
Groff
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'\"
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'\" Copyright (c) 1990 The Regents of the University of California.
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'\" All rights reserved.
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'\"
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'\" Permission is hereby granted, without written agreement and without
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'\" license or royalty fees, to use, copy, modify, and distribute this
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'\" documentation for any purpose, provided that the above copyright
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'\" notice and the following two paragraphs appear in all copies.
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'\"
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'\" IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
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'\" FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
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'\" ARISING OUT OF THE USE OF THIS DOCUMENTATION, EVEN IF THE UNIVERSITY OF
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'\" CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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'\"
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'\" THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
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'\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
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'\" AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
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'\" ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATION TO
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'\" PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
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'\"
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'\" $Header: /user6/ouster/wish/man/RCS/FileHndlr.3,v 1.7 93/04/01 09:41:21 ouster Exp $ SPRITE (Berkeley)
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'\"
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.so man.macros
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.HS Tk_CreateFileHandler tkc
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.BS
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.SH NAME
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Tk_CreateFileHandler, Tk_DeleteFileHandler \- associate procedure callback with a file or device
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.SH SYNOPSIS
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.nf
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\fB#include <tk.h>\fR
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.sp
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\fBTk_CreateFileHandler\fR(\fIid, mask, proc, clientData\fR)
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.sp
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\fBTk_DeleteFileHandler\fR(\fIid\fR)
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.SH ARGUMENTS
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.AS Tk_FileProc clientData
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.AP int id in
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Integer identifier for an open file or device (such as returned by
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\fBopen\fR system call).
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.AP int mask in
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Conditions under which \fIproc\fR should be called:
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OR-ed combination of \fBTK_READABLE\fR, \fBTK_WRITABLE\fR,
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and \fBTK_EXCEPTION\fR.
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.AP Tk_FileProc *proc in
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Procedure to invoke whenever the file or device indicated
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by \fIid\fR meets 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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\fBTk_CreateFileHandler\fR arranges for \fIproc\fR to be
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invoked in the future whenever I/O becomes possible on a file
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or an exceptional condition exists for the file. The file
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is indicated by \fIid\fR, and the conditions of interest
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are indicated by \fImask\fR. For example, if \fImask\fR
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is \fBTK_READABLE\fR, then \fIproc\fR will be called when
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the file is readable.
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The callback to \fIproc\fR is made by \fBTk_DoOneEvent\fR, so
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\fBTk_CreateFileHandler\fR is only useful
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in programs that dispatch events
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through \fBTk_DoOneEvent\fR or through other Tk procedures that
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call \fBTk_DoOneEvent\fR, such as \fBTk_MainLoop\fR.
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.PP
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\fIProc\fP should have arguments and result that match the
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type \fBTk_FileProc\fR:
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.nf
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.RS
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typedef void Tk_FileProc(
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.RS
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ClientData \fIclientData\fR,
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int \fImask\fR);
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.RE
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.RE
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.fi
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The \fIclientData\fP parameter to \fIproc\fR is a copy
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of the \fIclientData\fP
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argument given to \fBTcl_CreateFileHandler\fR when the callback
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was created. Typically, \fIclientData\fR points to a data
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structure containing application-specific information about
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the file. \fIMask\fR is an integer mask indicating which
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of the requested conditions actually exists for the file; it
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will contain a subset of the bits in the \fImask\fR argument
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to \fBTcl_CreateFileHandler\fR.
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.PP
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There may exist only one handler for a given file at a given
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time. If \fBTk_CreateEventHandler\fR is called when a handler
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already exists for \fIid\fR, then the \fImask\fR, \fIproc\fR,
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and \fIclientData\fR for the new call to
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\fBTk_CreateEventHandler\fR replace the information that was
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previously recorded.
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.PP
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\fBTk_DeleteFileHandler\fR may be called to delete the
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file handler for \fIid\fR; if no handler exists for the
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file given by \fIid\fR then the procedure has no effect.
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.PP
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The purpose of file handlers is to enable an application to
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respond to X events and other events while waiting for files
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to become ready for I/O. For this to work correctly, the
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application must use non-blocking I/O operations on the
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files for which handlers are declared. Otherwise the application
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may be put to sleep if it specifies too large an input or
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output buffer; while waiting for the I/O to complete the
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application won't be able to service other events. In BSD-based
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UNIX systems, non-blocking I/O can be specified for a file using
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the \fBfcntl\fR kernel call with the \fBFNDELAY\fR flag.
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.SH KEYWORDS
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callback, file, handler
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