| 1 | '\" |
| 2 | '\" Copyright (c) 1994 The Regents of the University of California. |
| 3 | '\" Copyright (c) 1994-1996 Sun Microsystems, Inc. |
| 4 | '\" |
| 5 | '\" See the file "license.terms" for information on usage and redistribution |
| 6 | '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. |
| 7 | '\" |
| 8 | '\" RCS: @(#) $Id: fileevent.n,v 1.5.6.1 2004/10/27 12:52:40 dkf Exp $ |
| 9 | '\" |
| 10 | '\" The definitions below are for supplemental macros used in Tcl/Tk |
| 11 | '\" manual entries. |
| 12 | '\" |
| 13 | '\" .AP type name in/out ?indent? |
| 14 | '\" Start paragraph describing an argument to a library procedure. |
| 15 | '\" type is type of argument (int, etc.), in/out is either "in", "out", |
| 16 | '\" or "in/out" to describe whether procedure reads or modifies arg, |
| 17 | '\" and indent is equivalent to second arg of .IP (shouldn't ever be |
| 18 | '\" needed; use .AS below instead) |
| 19 | '\" |
| 20 | '\" .AS ?type? ?name? |
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| 22 | '\" name are examples of largest possible arguments that will be passed |
| 23 | '\" to .AP later. If args are omitted, default tab stops are used. |
| 24 | '\" |
| 25 | '\" .BS |
| 26 | '\" Start box enclosure. From here until next .BE, everything will be |
| 27 | '\" enclosed in one large box. |
| 28 | '\" |
| 29 | '\" .BE |
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| 31 | '\" |
| 32 | '\" .CS |
| 33 | '\" Begin code excerpt. |
| 34 | '\" |
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| 37 | '\" |
| 38 | '\" .VS ?version? ?br? |
| 39 | '\" Begin vertical sidebar, for use in marking newly-changed parts |
| 40 | '\" of man pages. The first argument is ignored and used for recording |
| 41 | '\" the version when the .VS was added, so that the sidebars can be |
| 42 | '\" found and removed when they reach a certain age. If another argument |
| 43 | '\" is present, then a line break is forced before starting the sidebar. |
| 44 | '\" |
| 45 | '\" .VE |
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| 47 | '\" |
| 48 | '\" .DS |
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| 50 | '\" |
| 51 | '\" .DE |
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| 53 | '\" |
| 54 | '\" .SO |
| 55 | '\" Start of list of standard options for a Tk widget. The |
| 56 | '\" options follow on successive lines, in four columns separated |
| 57 | '\" by tabs. |
| 58 | '\" |
| 59 | '\" .SE |
| 60 | '\" End of list of standard options for a Tk widget. |
| 61 | '\" |
| 62 | '\" .OP cmdName dbName dbClass |
| 63 | '\" Start of description of a specific option. cmdName gives the |
| 64 | '\" option's name as specified in the class command, dbName gives |
| 65 | '\" the option's name in the option database, and dbClass gives |
| 66 | '\" the option's class in the option database. |
| 67 | '\" |
| 68 | '\" .UL arg1 arg2 |
| 69 | '\" Print arg1 underlined, then print arg2 normally. |
| 70 | '\" |
| 71 | '\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $ |
| 72 | '\" |
| 73 | '\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages. |
| 74 | .if t .wh -1.3i ^B |
| 75 | .nr ^l \n(.l |
| 76 | .ad b |
| 77 | '\" # Start an argument description |
| 78 | .de AP |
| 79 | .ie !"\\$4"" .TP \\$4 |
| 80 | .el \{\ |
| 81 | . ie !"\\$2"" .TP \\n()Cu |
| 82 | . el .TP 15 |
| 83 | .\} |
| 84 | .ta \\n()Au \\n()Bu |
| 85 | .ie !"\\$3"" \{\ |
| 86 | \&\\$1 \\fI\\$2\\fP (\\$3) |
| 87 | .\".b |
| 88 | .\} |
| 89 | .el \{\ |
| 90 | .br |
| 91 | .ie !"\\$2"" \{\ |
| 92 | \&\\$1 \\fI\\$2\\fP |
| 93 | .\} |
| 94 | .el \{\ |
| 95 | \&\\fI\\$1\\fP |
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| 98 | .. |
| 99 | '\" # define tabbing values for .AP |
| 100 | .de AS |
| 101 | .nr )A 10n |
| 102 | .if !"\\$1"" .nr )A \\w'\\$1'u+3n |
| 103 | .nr )B \\n()Au+15n |
| 104 | .\" |
| 105 | .if !"\\$2"" .nr )B \\w'\\$2'u+\\n()Au+3n |
| 106 | .nr )C \\n()Bu+\\w'(in/out)'u+2n |
| 107 | .. |
| 108 | .AS Tcl_Interp Tcl_CreateInterp in/out |
| 109 | '\" # BS - start boxed text |
| 110 | '\" # ^y = starting y location |
| 111 | '\" # ^b = 1 |
| 112 | .de BS |
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| 116 | .if n .nf |
| 117 | .if n .ti 0 |
| 118 | .if n \l'\\n(.lu\(ul' |
| 119 | .if n .fi |
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| 121 | '\" # BE - end boxed text (draw box now) |
| 122 | .de BE |
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| 126 | .ie n \l'\\n(^lu\(ul' |
| 127 | .el \{\ |
| 128 | .\" Draw four-sided box normally, but don't draw top of |
| 129 | .\" box if the box started on an earlier page. |
| 130 | .ie !\\n(^b-1 \{\ |
| 131 | \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' |
| 132 | .\} |
| 133 | .el \}\ |
| 134 | \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' |
| 135 | .\} |
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| 138 | .br |
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| 140 | .. |
| 141 | '\" # VS - start vertical sidebar |
| 142 | '\" # ^Y = starting y location |
| 143 | '\" # ^v = 1 (for troff; for nroff this doesn't matter) |
| 144 | .de VS |
| 145 | .if !"\\$2"" .br |
| 146 | .mk ^Y |
| 147 | .ie n 'mc \s12\(br\s0 |
| 148 | .el .nr ^v 1u |
| 149 | .. |
| 150 | '\" # VE - end of vertical sidebar |
| 151 | .de VE |
| 152 | .ie n 'mc |
| 153 | .el \{\ |
| 154 | .ev 2 |
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| 158 | \h'|\\n(^lu+3n'\L'|\\n(^Yu-1v\(bv'\v'\\n(^tu+1v-\\n(^Yu'\h'-|\\n(^lu+3n' |
| 159 | .sp -1 |
| 160 | .fi |
| 161 | .ev |
| 162 | .\} |
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| 164 | .. |
| 165 | '\" # Special macro to handle page bottom: finish off current |
| 166 | '\" # box/sidebar if in box/sidebar mode, then invoked standard |
| 167 | '\" # page bottom macro. |
| 168 | .de ^B |
| 169 | .ev 2 |
| 170 | 'ti 0 |
| 171 | 'nf |
| 172 | .mk ^t |
| 173 | .if \\n(^b \{\ |
| 174 | .\" Draw three-sided box if this is the box's first page, |
| 175 | .\" draw two sides but no top otherwise. |
| 176 | .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 |
| 177 | .el \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c |
| 178 | .\} |
| 179 | .if \\n(^v \{\ |
| 180 | .nr ^x \\n(^tu+1v-\\n(^Yu |
| 181 | \kx\h'-\\nxu'\h'|\\n(^lu+3n'\ky\L'-\\n(^xu'\v'\\n(^xu'\h'|0u'\c |
| 182 | .\} |
| 183 | .bp |
| 184 | 'fi |
| 185 | .ev |
| 186 | .if \\n(^b \{\ |
| 187 | .mk ^y |
| 188 | .nr ^b 2 |
| 189 | .\} |
| 190 | .if \\n(^v \{\ |
| 191 | .mk ^Y |
| 192 | .\} |
| 193 | .. |
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| 195 | .de DS |
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| 199 | .. |
| 200 | '\" # DE - end display |
| 201 | .de DE |
| 202 | .fi |
| 203 | .RE |
| 204 | .sp |
| 205 | .. |
| 206 | '\" # SO - start of list of standard options |
| 207 | .de SO |
| 208 | .SH "STANDARD OPTIONS" |
| 209 | .LP |
| 210 | .nf |
| 211 | .ta 5.5c 11c |
| 212 | .ft B |
| 213 | .. |
| 214 | '\" # SE - end of list of standard options |
| 215 | .de SE |
| 216 | .fi |
| 217 | .ft R |
| 218 | .LP |
| 219 | See the \\fBoptions\\fR manual entry for details on the standard options. |
| 220 | .. |
| 221 | '\" # OP - start of full description for a single option |
| 222 | .de OP |
| 223 | .LP |
| 224 | .nf |
| 225 | .ta 4c |
| 226 | Command-Line Name: \\fB\\$1\\fR |
| 227 | Database Name: \\fB\\$2\\fR |
| 228 | Database Class: \\fB\\$3\\fR |
| 229 | .fi |
| 230 | .IP |
| 231 | .. |
| 232 | '\" # CS - begin code excerpt |
| 233 | .de CS |
| 234 | .RS |
| 235 | .nf |
| 236 | .ta .25i .5i .75i 1i |
| 237 | .. |
| 238 | '\" # CE - end code excerpt |
| 239 | .de CE |
| 240 | .fi |
| 241 | .RE |
| 242 | .. |
| 243 | .de UL |
| 244 | \\$1\l'|0\(ul'\\$2 |
| 245 | .. |
| 246 | .TH fileevent n 7.5 Tcl "Tcl Built-In Commands" |
| 247 | .BS |
| 248 | '\" Note: do not modify the .SH NAME line immediately below! |
| 249 | .SH NAME |
| 250 | fileevent \- Execute a script when a channel becomes readable or writable |
| 251 | .SH SYNOPSIS |
| 252 | \fBfileevent \fIchannelId \fBreadable \fR?\fIscript\fR? |
| 253 | .sp |
| 254 | \fBfileevent \fIchannelId \fBwritable \fR?\fIscript\fR? |
| 255 | .BE |
| 256 | |
| 257 | .SH DESCRIPTION |
| 258 | .PP |
| 259 | This command is used to create \fIfile event handlers\fR. A file event |
| 260 | handler is a binding between a channel and a script, such that the script |
| 261 | is evaluated whenever the channel becomes readable or writable. File event |
| 262 | handlers are most commonly used to allow data to be received from another |
| 263 | process on an event-driven basis, so that the receiver can continue to |
| 264 | interact with the user while waiting for the data to arrive. If an |
| 265 | application invokes \fBgets\fR or \fBread\fR on a blocking channel when |
| 266 | there is no input data available, the process will block; until the input |
| 267 | data arrives, it will not be able to service other events, so it will |
| 268 | appear to the user to ``freeze up''. With \fBfileevent\fR, the process can |
| 269 | tell when data is present and only invoke \fBgets\fR or \fBread\fR when |
| 270 | they won't block. |
| 271 | .PP |
| 272 | .VS |
| 273 | The \fIchannelId\fR argument to \fBfileevent\fR refers to an open |
| 274 | channel such as a Tcl standard channel (\fBstdin\fR, \fBstdout\fR, |
| 275 | or \fBstderr\fR), the return value from an invocation of \fBopen\fR |
| 276 | or \fBsocket\fR, or the result of a channel creation command provided |
| 277 | by a Tcl extension. |
| 278 | .VE |
| 279 | .PP |
| 280 | If the \fIscript\fR argument is specified, then \fBfileevent\fR |
| 281 | creates a new event handler: \fIscript\fR will be evaluated |
| 282 | whenever the channel becomes readable or writable (depending on the |
| 283 | second argument to \fBfileevent\fR). |
| 284 | In this case \fBfileevent\fR returns an empty string. |
| 285 | The \fBreadable\fR and \fBwritable\fR event handlers for a file |
| 286 | are independent, and may be created and deleted separately. |
| 287 | However, there may be at most one \fBreadable\fR and one \fBwritable\fR |
| 288 | handler for a file at a given time in a given interpreter. |
| 289 | If \fBfileevent\fR is called when the specified handler already |
| 290 | exists in the invoking interpreter, the new script replaces the old one. |
| 291 | .PP |
| 292 | If the \fIscript\fR argument is not specified, \fBfileevent\fR |
| 293 | returns the current script for \fIchannelId\fR, or an empty string |
| 294 | if there is none. |
| 295 | If the \fIscript\fR argument is specified as an empty string |
| 296 | then the event handler is deleted, so that no script will be invoked. |
| 297 | A file event handler is also deleted automatically whenever |
| 298 | its channel is closed or its interpreter is deleted. |
| 299 | .PP |
| 300 | A channel is considered to be readable if there is unread data |
| 301 | available on the underlying device. |
| 302 | A channel is also considered to be readable if there is unread |
| 303 | data in an input buffer, except in the special case where the |
| 304 | most recent attempt to read from the channel was a \fBgets\fR |
| 305 | call that could not find a complete line in the input buffer. |
| 306 | This feature allows a file to be read a line at a time in nonblocking mode |
| 307 | using events. |
| 308 | A channel is also considered to be readable if an end of file or |
| 309 | error condition is present on the underlying file or device. |
| 310 | It is important for \fIscript\fR to check for these conditions |
| 311 | and handle them appropriately; for example, if there is no special |
| 312 | check for end of file, an infinite loop may occur where \fIscript\fR |
| 313 | reads no data, returns, and is immediately invoked again. |
| 314 | .PP |
| 315 | A channel is considered to be writable if at least one byte of data |
| 316 | can be written to the underlying file or device without blocking, |
| 317 | or if an error condition is present on the underlying file or device. |
| 318 | .PP |
| 319 | Event-driven I/O works best for channels that have been |
| 320 | placed into nonblocking mode with the \fBfconfigure\fR command. |
| 321 | In blocking mode, a \fBputs\fR command may block if you give it |
| 322 | more data than the underlying file or device can accept, and a |
| 323 | \fBgets\fR or \fBread\fR command will block if you attempt to read |
| 324 | more data than is ready; no events will be processed while the |
| 325 | commands block. |
| 326 | In nonblocking mode \fBputs\fR, \fBread\fR, and \fBgets\fR never block. |
| 327 | See the documentation for the individual commands for information |
| 328 | on how they handle blocking and nonblocking channels. |
| 329 | .PP |
| 330 | The script for a file event is executed at global level (outside the |
| 331 | context of any Tcl procedure) in the interpreter in which the |
| 332 | \fBfileevent\fR command was invoked. |
| 333 | If an error occurs while executing the script then the |
| 334 | \fBbgerror\fR mechanism is used to report the error. |
| 335 | In addition, the file event handler is deleted if it ever returns |
| 336 | an error; this is done in order to prevent infinite loops due to |
| 337 | buggy handlers. |
| 338 | .SH EXAMPLE |
| 339 | In this setup \fBGetData\fR will be called with the channel as an |
| 340 | argument whenever $chan becomes readable. |
| 341 | .CS |
| 342 | proc GetData {chan} { |
| 343 | if {![eof $chan]} { |
| 344 | puts [gets $chan] |
| 345 | } |
| 346 | } |
| 347 | |
| 348 | \fBfileevent\fR $chan readable [list GetData $chan] |
| 349 | .CE |
| 350 | |
| 351 | .SH CREDITS |
| 352 | .PP |
| 353 | \fBfileevent\fR is based on the \fBaddinput\fR command created |
| 354 | by Mark Diekhans. |
| 355 | |
| 356 | .SH "SEE ALSO" |
| 357 | bgerror(n), fconfigure(n), gets(n), puts(n), read(n), Tcl_StandardChannels(3) |
| 358 | |
| 359 | .SH KEYWORDS |
| 360 | asynchronous I/O, blocking, channel, event handler, nonblocking, readable, |
| 361 | script, writable. |