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markom |
'\"
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'\" Copyright (c) 1990-1992 The Regents of the University of California.
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'\" Copyright (c) 1994-1996 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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'\" RCS: @(#) $Id: DoOneEvent.3,v 1.1.1.1 2002-01-16 10:25:23 markom Exp $
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'\"
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.so man.macros
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.TH Tcl_DoOneEvent 3 7.5 Tcl "Tcl Library Procedures"
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.BS
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.SH NAME
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Tcl_DoOneEvent \- wait for events and invoke event handlers
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.SH SYNOPSIS
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.nf
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\fB#include \fR
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.sp
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int
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\fBTcl_DoOneEvent\fR(\fIflags\fR)
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.SH ARGUMENTS
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.AS int flags
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.AP int flags in
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This parameter is normally zero. It may be an OR-ed combination
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of any of the following flag bits:
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TCL_WINDOW_EVENTS,
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TCL_FILE_EVENTS, TCL_TIMER_EVENTS, TCL_IDLE_EVENTS, TCL_ALL_EVENTS, or
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TCL_DONT_WAIT.
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.BE
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.SH DESCRIPTION
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.PP
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This procedure is the entry point to Tcl's event loop; it is responsible for
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waiting for events and dispatching event handlers created with
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procedures such as \fBTk_CreateEventHandler\fR, \fBTcl_CreateFileHandler\fR,
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\fBTcl_CreateTimerHandler\fR, and \fBTcl_DoWhenIdle\fR.
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\fBTcl_DoOneEvent\fR checks to see if
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events are already present on the Tcl event queue; if so,
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it calls the handler(s) for the first (oldest) event, removes it from
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the queue, and returns.
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If there are no events ready to be handled, then \fBTcl_DoOneEvent\fR
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checks for new events from all possible sources.
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If any are found, it puts all of them on Tcl's event queue, calls
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handlers for the first event on the queue, and returns.
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If no events are found, \fBTcl_DoOneEvent\fR checks for \fBTcl_DoWhenIdle\fR
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callbacks; if any are found, it invokes all of them and returns.
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Finally, if no events or idle callbacks have been found, then
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\fBTcl_DoOneEvent\fR sleeps until an event occurs; then it adds any
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new events to the Tcl event queue, calls handlers for the first event,
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and returns.
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The normal return value is 1 to signify that some event
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was processed (see below for other alternatives).
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.PP
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If the \fIflags\fR argument to \fBTcl_DoOneEvent\fR is non-zero,
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it restricts the kinds of events that will be processed by
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\fBTcl_DoOneEvent\fR.
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\fIFlags\fR may be an OR-ed combination of any of the following bits:
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.TP 27
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\fBTCL_WINDOW_EVENTS\fR \-
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Process window system events.
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.TP 27
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\fBTCL_FILE_EVENTS\fR \-
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Process file events.
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.TP 27
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\fBTCL_TIMER_EVENTS\fR \-
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Process timer events.
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.TP 27
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\fBTCL_IDLE_EVENTS\fR \-
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Process idle callbacks.
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.TP 27
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\fBTCL_ALL_EVENTS\fR \-
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Process all kinds of events: equivalent to OR-ing together all of the
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above flags or specifying none of them.
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.TP 27
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\fBTCL_DONT_WAIT\fR \-
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Don't sleep: process only events that are ready at the time of the
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call.
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.LP
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If any of the flags \fBTCL_WINDOW_EVENTS\fR, \fBTCL_FILE_EVENTS\fR,
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\fBTCL_TIMER_EVENTS\fR, or \fBTCL_IDLE_EVENTS\fR is set, then the only
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events that will be considered are those for which flags are set.
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Setting none of these flags is equivalent to the value
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\fBTCL_ALL_EVENTS\fR, which causes all event types to be processed.
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If an application has defined additional event sources with
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\fBTcl_CreateEventSource\fR, then additional \fIflag\fR values
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may also be valid, depending on those event sources.
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.PP
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The \fBTCL_DONT_WAIT\fR flag causes \fBTcl_DoOneEvent\fR not to put
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the process to sleep: it will check for events but if none are found
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then it returns immediately with a return value of 0 to indicate
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that no work was done.
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\fBTcl_DoOneEvent\fR will also return 0 without doing anything if
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the only alternative is to block forever (this can happen, for example,
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if \fIflags\fR is \fBTCL_IDLE_EVENTS\fR and there are no
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\fBTcl_DoWhenIdle\fR callbacks pending, or if no event handlers or
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timer handlers exist).
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.PP
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\fBTcl_DoOneEvent\fR may be invoked recursively. For example,
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it is possible to invoke \fBTcl_DoOneEvent\fR recursively
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from a handler called by \fBTcl_DoOneEvent\fR. This sort
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of operation is useful in some modal situations, such
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as when a
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notification dialog has been popped up and an application wishes to
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wait for the user to click a button in the dialog before
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doing anything else.
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.SH KEYWORDS
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callback, event, handler, idle, timer
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