PeekIfEv.c revision 507fd43f 
1/*
2
3Copyright 1986, 1998  The Open Group
4
5Permission to use, copy, modify, distribute, and sell this software and its
6documentation for any purpose is hereby granted without fee, provided that
7the above copyright notice appear in all copies and that both that
8copyright notice and this permission notice appear in supporting
9documentation.
10
11The above copyright notice and this permission notice shall be included in
12all copies or substantial portions of the Software.
13
14THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
15IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
16FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
17OPEN GROUP BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
18AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
19CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
20
21Except as contained in this notice, the name of The Open Group shall not be
22used in advertising or otherwise to promote the sale, use or other dealings
23in this Software without prior written authorization from The Open Group.
24
25*/
26
27#ifdef HAVE_CONFIG_H
28#include <config.h>
29#endif
30#include "Xlibint.h"
31
32/*
33 * return the next event in the queue that satisfies the predicate.
34 * BUT do not remove it from the queue.
35 * If none found, flush, and then wait until one satisfies the predicate.
36 */
37
38int
39XPeekIfEvent (
40	register Display *dpy,
41	register XEvent *event,
42	Bool (*predicate)(
43			  Display*			/* display */,
44			  XEvent*			/* event */,
45			  char*				/* arg */
46			  ),
47	char *arg)
48{
49	register _XQEvent *prev, *qelt;
50	unsigned long qe_serial = 0;
51
52	dpy->in_ifevent++;
53	LockDisplay(dpy);
54	prev = NULL;
55	while (1) {
56	    for (qelt = prev ? prev->next : dpy->head;
57		 qelt;
58		 prev = qelt, qelt = qelt->next) {
59		if(qelt->qserial_num > qe_serial
60		   && (*predicate)(dpy, &qelt->event, arg)) {
61		    XEvent copy;
62		    *event = qelt->event;
63		    if (_XCopyEventCookie(dpy, &event->xcookie, &copy.xcookie)) {
64			_XStoreEventCookie(dpy, &copy);
65			*event = copy;
66		    }
67		    dpy->in_ifevent--;
68		    UnlockDisplay(dpy);
69		    return 0;
70		}
71	    }
72	    if (prev)
73		qe_serial = prev->qserial_num;
74	    _XReadEvents(dpy);
75	    if (prev && prev->qserial_num != qe_serial)
76		/* another thread has snatched this event */
77		prev = NULL;
78	}
79}
80
81