92 lines
3.5 KiB
Groff
92 lines
3.5 KiB
Groff
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'\"
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'\" Copyright (c) 1990-1994 The Regents of the University of California.
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'\" Copyright (c) 1994-1997 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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.TH Tcl_CreateFileHandler 3 8.0 Tcl "Tcl Library Procedures"
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.so man.macros
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.BS
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.SH NAME
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Tcl_CreateFileHandler, Tcl_DeleteFileHandler \- associate procedure callbacks with files or devices (Unix only)
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.SH SYNOPSIS
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.nf
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\fB#include <tcl.h>\fR
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.sp
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\fBTcl_CreateFileHandler\fR(\fIfd, mask, proc, clientData\fR)
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.sp
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\fBTcl_DeleteFileHandler\fR(\fIfd\fR)
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.SH ARGUMENTS
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.AS Tcl_FileProc clientData
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.AP int fd in
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Unix file descriptor for an open file or device.
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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 \fBTCL_READABLE\fR, \fBTCL_WRITABLE\fR,
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and \fBTCL_EXCEPTION\fR. May be set to 0 to temporarily disable
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a handler.
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.AP Tcl_FileProc *proc in
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Procedure to invoke whenever the file or device indicated
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by \fIfile\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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\fBTcl_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 \fIfd\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 \fBTCL_READABLE\fR, \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 \fBTcl_DoOneEvent\fR, so
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\fBTcl_CreateFileHandler\fR is only useful in programs that dispatch
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events through \fBTcl_DoOneEvent\fR or through Tcl commands such
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as \fBvwait\fR.
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.PP
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\fIProc\fR should have arguments and result that match the
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type \fBTcl_FileProc\fR:
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.PP
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.CS
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typedef void \fBTcl_FileProc\fR(
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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 parameter to \fIproc\fR is a copy
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of the \fIclientData\fR
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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 time.
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If \fBTcl_CreateFileHandler\fR is called when a handler already
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exists for \fIfd\fR, then the new callback replaces the information
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that was previously recorded.
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.PP
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\fBTcl_DeleteFileHandler\fR may be called to delete the
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file handler for \fIfd\fR; if no handler exists for the
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file given by \fIfd\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 respond to
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events while waiting for files to become ready for I/O. For this to work
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correctly, the application may need to use non-blocking I/O operations on
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the files for which handlers are declared. Otherwise the application may
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block if it reads or writes too much data; while waiting for the I/O to
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complete the application will not be able to service other events. Use
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\fBTcl_SetChannelOption\fR with \fB\-blocking\fR to set the channel into
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blocking or nonblocking mode as required.
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.PP
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Note that these interfaces are only supported by the Unix
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implementation of the Tcl notifier.
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.SH "SEE ALSO"
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fileevent(n), Tcl_CreateTimerHandler(3), Tcl_DoWhenIdle(3)
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.SH KEYWORDS
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callback, file, handler
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