'\" '\" Copyright (c) 1990-1994 The Regents of the University of California. '\" Copyright (c) 1994-1997 Sun Microsystems, Inc. '\" '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" '\" RCS: @(#) $Id: CrtFileHdlr.3,v 1.2 2001/09/14 01:42:08 zlaski Exp $ '\" .so man.macros .TH Tcl_CreateFileHandler 3 8.0 Tcl "Tcl Library Procedures" .BS .SH NAME Tcl_CreateFileHandler, Tcl_DeleteFileHandler \- associate procedure callbacks with files or devices (Unix only) .SH SYNOPSIS .nf \fB#include <tcl.h>\fR .VS .sp \fBTcl_CreateFileHandler\fR(\fIfd, mask, proc, clientData\fR) .sp \fBTcl_DeleteFileHandler\fR(\fIfd\fR) .VE .SH ARGUMENTS .AS Tcl_FileProc clientData .VS .AP int fd in Unix file descriptor for an open file or device. .VE .AP int mask in Conditions under which \fIproc\fR should be called: OR-ed combination of \fBTCL_READABLE\fR, \fBTCL_WRITABLE\fR, and \fBTCL_EXCEPTION\fR. May be set to 0 to temporarily disable a handler. .AP Tcl_FileProc *proc in Procedure to invoke whenever the file or device indicated by \fIfile\fR meets the conditions specified by \fImask\fR. .AP ClientData clientData in Arbitrary one-word value to pass to \fIproc\fR. .BE .SH DESCRIPTION .PP .VS \fBTcl_CreateFileHandler\fR arranges for \fIproc\fR to be invoked in the future whenever I/O becomes possible on a file or an exceptional condition exists for the file. The file is indicated by \fIfd\fR, and the conditions of interest .VE are indicated by \fImask\fR. For example, if \fImask\fR is \fBTCL_READABLE\fR, \fIproc\fR will be called when the file is readable. The callback to \fIproc\fR is made by \fBTcl_DoOneEvent\fR, so \fBTcl_CreateFileHandler\fR is only useful in programs that dispatch events through \fBTcl_DoOneEvent\fR or through Tcl commands such as \fBvwait\fR. .PP \fIProc\fR should have arguments and result that match the type \fBTcl_FileProc\fR: .CS typedef void Tcl_FileProc( ClientData \fIclientData\fR, int \fImask\fR); .CE The \fIclientData\fR parameter to \fIproc\fR is a copy of the \fIclientData\fR argument given to \fBTcl_CreateFileHandler\fR when the callback was created. Typically, \fIclientData\fR points to a data structure containing application-specific information about the file. \fIMask\fR is an integer mask indicating which of the requested conditions actually exists for the file; it will contain a subset of the bits in the \fImask\fR argument to \fBTcl_CreateFileHandler\fR. .PP .PP There may exist only one handler for a given file at a given time. If \fBTcl_CreateFileHandler\fR is called when a handler already exists for \fIfd\fR, then the new callback replaces the information that was previously recorded. .PP \fBTcl_DeleteFileHandler\fR may be called to delete the file handler for \fIfd\fR; if no handler exists for the file given by \fIfd\fR then the procedure has no effect. .PP The purpose of file handlers is to enable an application to respond to events while waiting for files to become ready for I/O. For this to work correctly, the application may need to use non-blocking I/O operations on the files for which handlers are declared. Otherwise the application may block if it reads or writes too much data; while waiting for the I/O to complete the application won't be able to service other events. Use \fBTcl_SetChannelOption\fR with \fB\-blocking\fR to set the channel into blocking or nonblocking mode as required. .PP .VS Note that these interfaces are only supported by the Unix implementation of the Tcl notifier. .VE .SH KEYWORDS callback, file, handler