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+/* $Xorg: PeekIfEv.c,v 1.4 2001/02/09 02:03:35 xorgcvs Exp $ */
+/*
+
+Copyright 1986, 1998 The Open Group
+
+Permission to use, copy, modify, distribute, and sell this software and its
+documentation for any purpose is hereby granted without fee, provided that
+the above copyright notice appear in all copies and that both that
+copyright notice and this permission notice appear in supporting
+documentation.
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+OPEN GROUP BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+Except as contained in this notice, the name of The Open Group shall not be
+used in advertising or otherwise to promote the sale, use or other dealings
+in this Software without prior written authorization from The Open Group.
+
+*/
+/* $XFree86: xc/lib/X11/PeekIfEv.c,v 1.4 2001/12/14 19:54:03 dawes Exp $ */
+
+#define NEED_EVENTS
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+#include "Xlibint.h"
+
+/*
+ * return the next event in the queue that satisfies the predicate.
+ * BUT do not remove it from the queue.
+ * If none found, flush, and then wait until one satisfies the predicate.
+ */
+
+int
+XPeekIfEvent (
+ register Display *dpy,
+ register XEvent *event,
+ Bool (*predicate)(
+ Display* /* display */,
+ XEvent* /* event */,
+ char* /* arg */
+ ),
+ char *arg)
+{
+ register _XQEvent *prev, *qelt;
+ unsigned long qe_serial = 0;
+
+ LockDisplay(dpy);
+ prev = NULL;
+ while (1) {
+ for (qelt = prev ? prev->next : dpy->head;
+ qelt;
+ prev = qelt, qelt = qelt->next) {
+ if(qelt->qserial_num > qe_serial
+ && (*predicate)(dpy, &qelt->event, arg)) {
+ *event = qelt->event;
+ UnlockDisplay(dpy);
+ return 0;
+ }
+ }
+ if (prev)
+ qe_serial = prev->qserial_num;
+ _XReadEvents(dpy);
+ if (prev && prev->qserial_num != qe_serial)
+ /* another thread has snatched this event */
+ prev = NULL;
+ }
+}
+