| '\" |
| '\" Copyright (c) 1994 The Regents of the University of California. |
| '\" Copyright (c) 1994-1996 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: fileevent.n,v 1.5 2001/09/27 05:50:56 andreas_kupries Exp $ |
| '\" |
| '\" The definitions below are for supplemental macros used in Tcl/Tk |
| '\" manual entries. |
| '\" |
| '\" .AP type name in/out ?indent? |
| '\" Start paragraph describing an argument to a library procedure. |
| '\" type is type of argument (int, etc.), in/out is either "in", "out", |
| '\" or "in/out" to describe whether procedure reads or modifies arg, |
| '\" and indent is equivalent to second arg of .IP (shouldn't ever be |
| '\" needed; use .AS below instead) |
| '\" |
| '\" .AS ?type? ?name? |
| '\" Give maximum sizes of arguments for setting tab stops. Type and |
| '\" name are examples of largest possible arguments that will be passed |
| '\" to .AP later. If args are omitted, default tab stops are used. |
| '\" |
| '\" .BS |
| '\" Start box enclosure. From here until next .BE, everything will be |
| '\" enclosed in one large box. |
| '\" |
| '\" .BE |
| '\" End of box enclosure. |
| '\" |
| '\" .CS |
| '\" Begin code excerpt. |
| '\" |
| '\" .CE |
| '\" End code excerpt. |
| '\" |
| '\" .VS ?version? ?br? |
| '\" Begin vertical sidebar, for use in marking newly-changed parts |
| '\" of man pages. The first argument is ignored and used for recording |
| '\" the version when the .VS was added, so that the sidebars can be |
| '\" found and removed when they reach a certain age. If another argument |
| '\" is present, then a line break is forced before starting the sidebar. |
| '\" |
| '\" .VE |
| '\" End of vertical sidebar. |
| '\" |
| '\" .DS |
| '\" Begin an indented unfilled display. |
| '\" |
| '\" .DE |
| '\" End of indented unfilled display. |
| '\" |
| '\" .SO |
| '\" Start of list of standard options for a Tk widget. The |
| '\" options follow on successive lines, in four columns separated |
| '\" by tabs. |
| '\" |
| '\" .SE |
| '\" End of list of standard options for a Tk widget. |
| '\" |
| '\" .OP cmdName dbName dbClass |
| '\" Start of description of a specific option. cmdName gives the |
| '\" option's name as specified in the class command, dbName gives |
| '\" the option's name in the option database, and dbClass gives |
| '\" the option's class in the option database. |
| '\" |
| '\" .UL arg1 arg2 |
| '\" Print arg1 underlined, then print arg2 normally. |
| '\" |
| '\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $ |
| '\" |
| '\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages. |
| .if t .wh -1.3i ^B |
| .nr ^l \n(.l |
| .ad b |
| '\" # Start an argument description |
| .de AP |
| .ie !"\\$4"" .TP \\$4 |
| .el \{\ |
| . ie !"\\$2"" .TP \\n()Cu |
| . el .TP 15 |
| .\} |
| .ta \\n()Au \\n()Bu |
| .ie !"\\$3"" \{\ |
| \&\\$1 \\fI\\$2\\fP (\\$3) |
| .\".b |
| .\} |
| .el \{\ |
| .br |
| .ie !"\\$2"" \{\ |
| \&\\$1 \\fI\\$2\\fP |
| .\} |
| .el \{\ |
| \&\\fI\\$1\\fP |
| .\} |
| .\} |
| .. |
| '\" # define tabbing values for .AP |
| .de AS |
| .nr )A 10n |
| .if !"\\$1"" .nr )A \\w'\\$1'u+3n |
| .nr )B \\n()Au+15n |
| .\" |
| .if !"\\$2"" .nr )B \\w'\\$2'u+\\n()Au+3n |
| .nr )C \\n()Bu+\\w'(in/out)'u+2n |
| .. |
| .AS Tcl_Interp Tcl_CreateInterp in/out |
| '\" # BS - start boxed text |
| '\" # ^y = starting y location |
| '\" # ^b = 1 |
| .de BS |
| .br |
| .mk ^y |
| .nr ^b 1u |
| .if n .nf |
| .if n .ti 0 |
| .if n \l'\\n(.lu\(ul' |
| .if n .fi |
| .. |
| '\" # BE - end boxed text (draw box now) |
| .de BE |
| .nf |
| .ti 0 |
| .mk ^t |
| .ie n \l'\\n(^lu\(ul' |
| .el \{\ |
| .\" Draw four-sided box normally, but don't draw top of |
| .\" box if the box started on an earlier page. |
| .ie !\\n(^b-1 \{\ |
| \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' |
| .\} |
| .el \}\ |
| \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' |
| .\} |
| .\} |
| .fi |
| .br |
| .nr ^b 0 |
| .. |
| '\" # VS - start vertical sidebar |
| '\" # ^Y = starting y location |
| '\" # ^v = 1 (for troff; for nroff this doesn't matter) |
| .de VS |
| .if !"\\$2"" .br |
| .mk ^Y |
| .ie n 'mc \s12\(br\s0 |
| .el .nr ^v 1u |
| .. |
| '\" # VE - end of vertical sidebar |
| .de VE |
| .ie n 'mc |
| .el \{\ |
| .ev 2 |
| .nf |
| .ti 0 |
| .mk ^t |
| \h'|\\n(^lu+3n'\L'|\\n(^Yu-1v\(bv'\v'\\n(^tu+1v-\\n(^Yu'\h'-|\\n(^lu+3n' |
| .sp -1 |
| .fi |
| .ev |
| .\} |
| .nr ^v 0 |
| .. |
| '\" # Special macro to handle page bottom: finish off current |
| '\" # box/sidebar if in box/sidebar mode, then invoked standard |
| '\" # page bottom macro. |
| .de ^B |
| .ev 2 |
| 'ti 0 |
| 'nf |
| .mk ^t |
| .if \\n(^b \{\ |
| .\" Draw three-sided box if this is the box's first page, |
| .\" draw two sides but no top otherwise. |
| .ie !\\n(^b-1 \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c |
| .el \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c |
| .\} |
| .if \\n(^v \{\ |
| .nr ^x \\n(^tu+1v-\\n(^Yu |
| \kx\h'-\\nxu'\h'|\\n(^lu+3n'\ky\L'-\\n(^xu'\v'\\n(^xu'\h'|0u'\c |
| .\} |
| .bp |
| 'fi |
| .ev |
| .if \\n(^b \{\ |
| .mk ^y |
| .nr ^b 2 |
| .\} |
| .if \\n(^v \{\ |
| .mk ^Y |
| .\} |
| .. |
| '\" # DS - begin display |
| .de DS |
| .RS |
| .nf |
| .sp |
| .. |
| '\" # DE - end display |
| .de DE |
| .fi |
| .RE |
| .sp |
| .. |
| '\" # SO - start of list of standard options |
| .de SO |
| .SH "STANDARD OPTIONS" |
| .LP |
| .nf |
| .ta 5.5c 11c |
| .ft B |
| .. |
| '\" # SE - end of list of standard options |
| .de SE |
| .fi |
| .ft R |
| .LP |
| See the \\fBoptions\\fR manual entry for details on the standard options. |
| .. |
| '\" # OP - start of full description for a single option |
| .de OP |
| .LP |
| .nf |
| .ta 4c |
| Command-Line Name: \\fB\\$1\\fR |
| Database Name: \\fB\\$2\\fR |
| Database Class: \\fB\\$3\\fR |
| .fi |
| .IP |
| .. |
| '\" # CS - begin code excerpt |
| .de CS |
| .RS |
| .nf |
| .ta .25i .5i .75i 1i |
| .. |
| '\" # CE - end code excerpt |
| .de CE |
| .fi |
| .RE |
| .. |
| .de UL |
| \\$1\l'|0\(ul'\\$2 |
| .. |
| .TH fileevent n 7.5 Tcl "Tcl Built-In Commands" |
| .BS |
| '\" Note: do not modify the .SH NAME line immediately below! |
| .SH NAME |
| fileevent \- Execute a script when a channel becomes readable or writable |
| .SH SYNOPSIS |
| \fBfileevent \fIchannelId \fBreadable \fR?\fIscript\fR? |
| .sp |
| \fBfileevent \fIchannelId \fBwritable \fR?\fIscript\fR? |
| .BE |
| |
| .SH DESCRIPTION |
| .PP |
| This command is used to create \fIfile event handlers\fR. A file event |
| handler is a binding between a channel and a script, such that the script |
| is evaluated whenever the channel becomes readable or writable. File event |
| handlers are most commonly used to allow data to be received from another |
| process on an event-driven basis, so that the receiver can continue to |
| interact with the user while waiting for the data to arrive. If an |
| application invokes \fBgets\fR or \fBread\fR on a blocking channel when |
| there is no input data available, the process will block; until the input |
| data arrives, it will not be able to service other events, so it will |
| appear to the user to ``freeze up''. With \fBfileevent\fR, the process can |
| tell when data is present and only invoke \fBgets\fR or \fBread\fR when |
| they won't block. |
| .PP |
| .VS |
| The \fIchannelId\fR argument to \fBfileevent\fR refers to 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. |
| .VE |
| .PP |
| If the \fIscript\fR argument is specified, then \fBfileevent\fR |
| creates a new event handler: \fIscript\fR will be evaluated |
| whenever the channel becomes readable or writable (depending on the |
| second argument to \fBfileevent\fR). |
| In this case \fBfileevent\fR returns an empty string. |
| The \fBreadable\fR and \fBwritable\fR event handlers for a file |
| are independent, and may be created and deleted separately. |
| However, there may be at most one \fBreadable\fR and one \fBwritable\fR |
| handler for a file at a given time in a given interpreter. |
| If \fBfileevent\fR is called when the specified handler already |
| exists in the invoking interpreter, the new script replaces the old one. |
| .PP |
| If the \fIscript\fR argument is not specified, \fBfileevent\fR |
| returns the current script for \fIchannelId\fR, or an empty string |
| if there is none. |
| If the \fIscript\fR argument is specified as an empty string |
| then the event handler is deleted, so that no script will be invoked. |
| A file event handler is also deleted automatically whenever |
| its channel is closed or its interpreter is deleted. |
| .PP |
| A channel is considered to be readable if there is unread data |
| available on the underlying device. |
| A channel is also considered to be readable if there is unread |
| data in an input buffer, except in the special case where the |
| most recent attempt to read from the channel was a \fBgets\fR |
| call that could not find a complete line in the input buffer. |
| This feature allows a file to be read a line at a time in nonblocking mode |
| using events. |
| A channel is also considered to be readable if an end of file or |
| error condition is present on the underlying file or device. |
| It is important for \fIscript\fR to check for these conditions |
| and handle them appropriately; for example, if there is no special |
| check for end of file, an infinite loop may occur where \fIscript\fR |
| reads no data, returns, and is immediately invoked again. |
| .PP |
| A channel is considered to be writable if at least one byte of data |
| can be written to the underlying file or device without blocking, |
| or if an error condition is present on the underlying file or device. |
| .PP |
| Event-driven I/O works best for channels that have been |
| placed into nonblocking mode with the \fBfconfigure\fR command. |
| In blocking mode, a \fBputs\fR command may block if you give it |
| more data than the underlying file or device can accept, and a |
| \fBgets\fR or \fBread\fR command will block if you attempt to read |
| more data than is ready; no events will be processed while the |
| commands block. |
| In nonblocking mode \fBputs\fR, \fBread\fR, and \fBgets\fR never block. |
| See the documentation for the individual commands for information |
| on how they handle blocking and nonblocking channels. |
| .PP |
| The script for a file event is executed at global level (outside the |
| context of any Tcl procedure) in the interpreter in which the |
| \fBfileevent\fR command was invoked. |
| If an error occurs while executing the script then the |
| \fBbgerror\fR mechanism is used to report the error. |
| In addition, the file event handler is deleted if it ever returns |
| an error; this is done in order to prevent infinite loops due to |
| buggy handlers. |
| |
| .SH EXAMPLE |
| .PP |
| .CS |
| proc GetData {chan} { |
| if {![eof $chan]} { |
| puts [gets $chan] |
| } |
| } |
| |
| fileevent $chan readable [list GetData $chan] |
| |
| .CE |
| In this setup \fBGetData\fR will be called with the channel as an |
| argument whenever $chan becomes readable. |
| |
| .SH CREDITS |
| .PP |
| \fBfileevent\fR is based on the \fBaddinput\fR command created |
| by Mark Diekhans. |
| |
| .SH "SEE ALSO" |
| bgerror(n), fconfigure(n), gets(n), puts(n), read(n), Tcl_StandardChannels(3) |
| |
| .SH KEYWORDS |
| asynchronous I/O, blocking, channel, event handler, nonblocking, readable, |
| script, writable. |