2 '\" Copyright (c
) 1994 The Regents of the University of California
.
3 '\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
5 '\" See the file "license.terms" for information on usage and redistribution
6 '\" of
this file
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8 '\" RCS
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(#) $Id: fileevent.n,v 1.1 2003/12/20 03:31:54 bbbush Exp $
10 '\" The definitions below are
for supplemental macros used
in Tcl
/Tk
13 '\" .AP type name in/out ?indent?
14 '\" Start paragraph describing an argument to a library procedure
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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
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17 '\" and indent is equivalent to second arg of .IP (shouldn't ever be
18 '\" needed; use .AS below instead)
21 '\" Give maximum sizes of arguments
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22 '\" name are examples of largest possible arguments that will be passed
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26 '\" Start box enclosure. From here until next .BE, everything will be
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33 '\" Begin code excerpt
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38 '\" .VS ?version? ?br?
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56 '\" options follow on successive lines, in four columns separated
60 '\" End of list of standard options for a Tk widget.
62 '\" .OP cmdName dbName dbClass
63 '\" Start of description of a specific option
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64 '\" option's name
as specified
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class command
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65 '\" the option's name
in the option database
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66 '\" the option's
class in the option database
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69 '\" Print arg1 underlined, then print arg2 normally.
71 '\" RCS: @(#) $Id: fileevent.n,v 1.1 2003/12/20 03:31:54 bbbush Exp $
73 '\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages.
77 '\" # Start an argument description
81 . ie !"\\$2
"" .TP
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86 \&\\$1 \\fI\\$2\\fP (\\$3)
99 '\" # define tabbing values for .AP
102 .if !"\\$1"" .nr )A \\w'\\$1
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105 .if !"\\$2"" .nr )B \\w'\\$2
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106 .nr )C \\n()Bu+\\w'(in/out)'u+2n
108 .AS Tcl_Interp Tcl_CreateInterp in/out
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118 .if n \l
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126 .ie n \l'\\n(^lu\
(ul
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128 .\" Draw four-sided box normally, but don't draw top of
129 .\" box
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131 \h
'-1.5n'\L
'|\\n(^yu-1v'\l
'\\n(^lu+3n\(ul'\L
'\\n(^tu+1v-\\n(^yu'\l
'|0u-1.5n\(ul'
134 \h
'-1.5n'\L
'|\\n(^yu-1v'\h
'\\n(^lu+3n'\L
'\\n(^tu+1v-\\n(^yu'\l
'|0u-1.5n\(ul'
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142 '\" # ^Y = starting y location
143 '\" # ^v = 1 (for troff; for nroff this doesn't matter
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147 .ie n 'mc \s12\(br\s0
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158 \h'|\\n(^lu+3n'\L'|\\n(^Yu-1v\(bv'\v'\\n(^tu+1v-\\n(^Yu'\h'-|\\n(^lu+3n'
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166 '\" # box/sidebar if in box/sidebar mode, then invoked standard
167 '\" # page bottom macro.
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
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
194 '\" # DS - begin display
200 '\" # DE - end display
206 '\" # SO - start of list of standard options
208 .SH "STANDARD OPTIONS
"
214 '\" # SE - end of list of standard options
219 See the \\fBoptions\\fR manual entry for details on the standard options.
221 '\" # OP - start of full description for a single option
226 Command-Line Name: \\fB\\$1\\fR
227 Database Name: \\fB\\$2\\fR
228 Database Class: \\fB\\$3\\fR
232 '\" # CS - begin code excerpt
238 '\" # CE - end code excerpt
246 .TH fileevent n 7.5 Tcl "Tcl Built
-In Commands
"
248 '\" Note: do not modify the .SH NAME line immediately below!
250 fileevent \- Execute a script when a channel becomes readable or writable
252 \fBfileevent \fIchannelId \fBreadable \fR?\fIscript\fR?
254 \fBfileevent \fIchannelId \fBwritable \fR?\fIscript\fR?
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
272 The \fIchannelId\fR argument to \fBfileevent\fR refers to an open channel,
273 such as the return value from a previous \fBopen\fR or \fBsocket\fR
275 If the \fIscript\fR argument is specified, then \fBfileevent\fR
276 creates a new event handler: \fIscript\fR will be evaluated
277 whenever the channel becomes readable or writable (depending on the
278 second argument to \fBfileevent\fR).
279 In this case \fBfileevent\fR returns an empty string.
280 The \fBreadable\fR and \fBwritable\fR event handlers for a file
281 are independent, and may be created and deleted separately.
282 However, there may be at most one \fBreadable\fR and one \fBwritable\fR
283 handler for a file at a given time in a given interpreter.
284 If \fBfileevent\fR is called when the specified handler already
285 exists in the invoking interpreter, the new script replaces the old one.
287 If the \fIscript\fR argument is not specified, \fBfileevent\fR
288 returns the current script for \fIchannelId\fR, or an empty string
290 If the \fIscript\fR argument is specified as an empty string
291 then the event handler is deleted, so that no script will be invoked.
292 A file event handler is also deleted automatically whenever
293 its channel is closed or its interpreter is deleted.
295 A channel is considered to be readable if there is unread data
296 available on the underlying device.
297 A channel is also considered to be readable if there is unread
298 data in an input buffer, except in the special case where the
299 most recent attempt to read from the channel was a \fBgets\fR
300 call that could not find a complete line in the input buffer.
301 This feature allows a file to be read a line at a time in nonblocking mode
303 A channel is also considered to be readable if an end of file or
304 error condition is present on the underlying file or device.
305 It is important for \fIscript\fR to check for these conditions
306 and handle them appropriately; for example, if there is no special
307 check for end of file, an infinite loop may occur where \fIscript\fR
308 reads no data, returns, and is immediately invoked again.
310 A channel is considered to be writable if at least one byte of data
311 can be written to the underlying file or device without blocking,
312 or if an error condition is present on the underlying file or device.
314 Event-driven I/O works best for channels that have been
315 placed into nonblocking mode with the \fBfconfigure\fR command.
316 In blocking mode, a \fBputs\fR command may block if you give it
317 more data than the underlying file or device can accept, and a
318 \fBgets\fR or \fBread\fR command will block if you attempt to read
319 more data than is ready; no events will be processed while the
321 In nonblocking mode \fBputs\fR, \fBread\fR, and \fBgets\fR never block.
322 See the documentation for the individual commands for information
323 on how they handle blocking and nonblocking channels.
325 The script for a file event is executed at global level (outside the
326 context of any Tcl procedure) in the interpreter in which the
327 \fBfileevent\fR command was invoked.
328 If an error occurs while executing the script then the
329 \fBbgerror\fR mechanism is used to report the error.
330 In addition, the file event handler is deleted if it ever returns
331 an error; this is done in order to prevent infinite loops due to
336 \fBfileevent\fR is based on the \fBaddinput\fR command created
340 bgerror(n), fconfigure(n), gets(n), puts(n), read(n)
343 asynchronous I/O, blocking, channel, event handler, nonblocking, readable,