Completely get rid of races during Motif drag window creation
* src/xterm.c (x_special_window_exists_p): New function. (xm_get_drag_window_1): Rework workflow and display grabbing.
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Po Lu
parent
9230953f23
commit
50b3e9d23d
1 changed files with 96 additions and 83 deletions
179
src/xterm.c
179
src/xterm.c
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@ -1838,10 +1838,47 @@ xm_drag_window_io_error_handler (Display *dpy)
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siglongjmp (x_dnd_disconnect_handler, 1);
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}
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/* Determine whether or not WINDOW exists on DPYINFO by selecting for
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input from it. */
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static bool
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x_special_window_exists_p (struct x_display_info *dpyinfo,
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Window window)
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{
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bool rc;
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x_catch_errors (dpyinfo->display);
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XSelectInput (dpyinfo->display, window,
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StructureNotifyMask);
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rc = !x_had_errors_p (dpyinfo->display);
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x_uncatch_errors_after_check ();
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return rc;
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}
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/* Drag window creation strategy (very tricky, but race-free):
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First look for _MOTIF_DRAG_WINDOW. If it is already present,
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return it immediately to avoid the overhead of new display
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connections.
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Otherwise, create a new connection to the display. In that
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connection, create a window, which will be the new drag window. Set
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the client disconnect mode of the new connection to
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RetainPermanent, and close it.
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Grab the current display. Look up _MOTIF_DRAG_WINDOW, the current
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drag window. If it exists (which means _MOTIF_DRAG_WINDOW was
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created between the first step and now), kill the client that
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created the new drag window to free the client slot on the X
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server. Otherwise, set _MOTIF_DRAG_WINDOW to the new drag window.
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Ungrab the display and return whichever window is currently in
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_MOTIF_DRAG_WINDOW. */
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static Window
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xm_get_drag_window_1 (struct x_display_info *dpyinfo)
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{
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Atom actual_type, _MOTIF_DRAG_WINDOW;
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Atom actual_type;
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int rc, actual_format;
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unsigned long nitems, bytes_remaining;
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unsigned char *tmp_data = NULL;
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@ -1851,9 +1888,9 @@ xm_get_drag_window_1 (struct x_display_info *dpyinfo)
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Emacs_XErrorHandler old_handler;
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Emacs_XIOErrorHandler old_io_handler;
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/* These are volatile because GCC mistakenly warns about them being
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/* This is volatile because GCC mistakenly warns about them being
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clobbered by longjmp. */
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volatile bool error, created;
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volatile bool error;
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drag_window = None;
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rc = XGetWindowProperty (dpyinfo->display, dpyinfo->root_window,
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@ -1862,26 +1899,20 @@ xm_get_drag_window_1 (struct x_display_info *dpyinfo)
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&actual_format, &nitems, &bytes_remaining,
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&tmp_data) == Success;
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if (rc)
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if (rc && actual_type == XA_WINDOW
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&& actual_format == 32 && nitems == 1
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&& tmp_data)
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{
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if (actual_type == XA_WINDOW
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&& actual_format == 32 && nitems == 1)
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{
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drag_window = *(Window *) tmp_data;
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x_catch_errors (dpyinfo->display);
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XSelectInput (dpyinfo->display, drag_window,
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StructureNotifyMask);
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rc = !x_had_errors_p (dpyinfo->display);
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x_uncatch_errors_after_check ();
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drag_window = *(Window *) tmp_data;
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rc = x_special_window_exists_p (dpyinfo, drag_window);
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if (!rc)
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drag_window = None;
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}
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if (tmp_data)
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XFree (tmp_data);
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if (!rc)
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drag_window = None;
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}
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if (tmp_data)
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XFree (tmp_data);
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if (drag_window == None)
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{
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block_input ();
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@ -1910,74 +1941,22 @@ xm_get_drag_window_1 (struct x_display_info *dpyinfo)
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error = false;
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xm_drag_window_error = &error;
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XGrabServer (temp_display);
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XSetCloseDownMode (temp_display, RetainPermanent);
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old_handler = XSetErrorHandler (xm_drag_window_error_handler);
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_MOTIF_DRAG_WINDOW = XInternAtom (temp_display,
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"_MOTIF_DRAG_WINDOW", False);
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if (error)
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goto give_up;
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/* Some other program might've created a drag window between now
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and when we first looked. Use that if it exists. */
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tmp_data = NULL;
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rc = XGetWindowProperty (temp_display, DefaultRootWindow (temp_display),
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_MOTIF_DRAG_WINDOW, 0, 1, False, XA_WINDOW,
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&actual_type, &actual_format, &nitems,
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&bytes_remaining, &tmp_data) == Success;
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if (rc && actual_type == XA_WINDOW
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&& actual_format == 32 && nitems == 1
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&& tmp_data)
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drag_window = *(Window *) tmp_data;
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if (tmp_data)
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XFree (tmp_data);
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error = false;
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if (drag_window == None)
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{
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created = true;
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attrs.override_redirect = True;
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drag_window = XCreateWindow (temp_display, DefaultRootWindow (temp_display),
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-1, -1, 1, 1, 0, CopyFromParent, InputOnly,
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CopyFromParent, CWOverrideRedirect, &attrs);
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XChangeProperty (temp_display, DefaultRootWindow (temp_display),
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_MOTIF_DRAG_WINDOW, XA_WINDOW, 32, PropModeReplace,
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(unsigned char *) &drag_window, 1);
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}
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else
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created = false;
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attrs.override_redirect = True;
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drag_window = XCreateWindow (temp_display, DefaultRootWindow (temp_display),
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-1, -1, 1, 1, 0, CopyFromParent, InputOnly,
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CopyFromParent, CWOverrideRedirect, &attrs);
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/* Handle all errors now. */
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XSync (temp_display, False);
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give_up:
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/* Some part of the drag window creation process failed, so
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punt. */
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punt. Release all resources too. */
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if (error)
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{
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XSetCloseDownMode (temp_display, DestroyAll);
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/* If the drag window was actually created, delete it now.
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Probably, a BadAlloc happened during the XChangeProperty
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request. */
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if (created)
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{
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if (drag_window != None)
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XDestroyWindow (temp_display, drag_window);
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XDeleteProperty (temp_display, DefaultRootWindow (temp_display),
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_MOTIF_DRAG_WINDOW);
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}
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drag_window = None;
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}
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@ -1995,15 +1974,49 @@ xm_get_drag_window_1 (struct x_display_info *dpyinfo)
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/* Make sure the drag window created is actually valid for the
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current display, and the XOpenDisplay above didn't
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accidentally connect to some other display. */
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x_catch_errors (dpyinfo->display);
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XSelectInput (dpyinfo->display, drag_window, StructureNotifyMask);
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rc = !x_had_errors_p (dpyinfo->display);
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x_uncatch_errors_after_check ();
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if (!x_special_window_exists_p (dpyinfo, drag_window))
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drag_window = None;
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unblock_input ();
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/* We connected to the wrong display, so just give up. */
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if (!rc)
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drag_window = None;
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if (drag_window != None)
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{
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XGrabServer (dpyinfo->display);
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x_catch_errors (dpyinfo->display);
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tmp_data = NULL;
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rc = XGetWindowProperty (dpyinfo->display, dpyinfo->root_window,
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dpyinfo->Xatom_MOTIF_DRAG_WINDOW,
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0, 1, False, XA_WINDOW, &actual_type,
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&actual_format, &nitems, &bytes_remaining,
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&tmp_data) == Success;
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if (rc && actual_type == XA_WINDOW
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&& actual_format == 32 && nitems == 1
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&& tmp_data
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&& x_special_window_exists_p (dpyinfo,
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*(Window *) tmp_data))
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{
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/* Kill the client now to avoid leaking a client slot,
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which is a limited resource. */
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XKillClient (dpyinfo->display, drag_window);
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drag_window = *(Window *) tmp_data;
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}
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else
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XChangeProperty (dpyinfo->display, dpyinfo->root_window,
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dpyinfo->Xatom_MOTIF_DRAG_WINDOW,
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XA_WINDOW, 32, PropModeReplace,
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(unsigned char *) &drag_window, 1);
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if (tmp_data)
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XFree (tmp_data);
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if (x_had_errors_p (dpyinfo->display))
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drag_window = None;
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x_uncatch_errors ();
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XUngrabServer (dpyinfo->display);
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}
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}
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return drag_window;
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