xterm.c.27.1.patch

diff --git a/src/xterm.c b/src/xterm.c
index 01ff790831..1acff2af0d 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -235,6 +235,117 @@ #define XtNinitialState "initialState"
 
 static bool x_get_current_wm_state (struct frame *, Window, int *, bool *);
 
+
+#define CLOCKID CLOCK_REALTIME
+#define CONN_SIG (SIGRTMAX-1)
+#include <signal.h>
+#include "X11/Xlibint.h"
+
+static int connection_fd = -1;
+void
+connection_timeout_handler (int signum)
+{
+    if (connection_fd != -1) {
+        close(connection_fd);
+        connection_fd = -1;
+    }
+}
+Status
+XCheckConnection (
+    register Display *dpy,
+    Drawable d, int fd, double timeout)
+{
+
+    xGetGeometryReply rep;
+    register xResourceReq *req;
+    LockDisplay(dpy);
+    GetResReq(GetGeometry, d, req);
+    Status res = 0;
+
+    sigset_t origmask;
+    sigset_t sigmask;
+    sigemptyset(&sigmask);
+    pthread_sigmask(SIG_SETMASK, &sigmask, &origmask);
+
+    // Create the timer
+    timer_t timerid;
+    struct sigevent sev;
+    struct itimerspec its;
+    long long freq_nanosecs;
+
+    struct sigaction new_action, old_action;
+
+    new_action.sa_handler = connection_timeout_handler;
+    sigemptyset (&new_action.sa_mask);
+    new_action.sa_flags = 0;
+
+    sigaction (CONN_SIG, &new_action, &old_action);
+
+    sev.sigev_notify = SIGEV_SIGNAL;
+    sev.sigev_signo = CONN_SIG;
+    sev.sigev_value.sival_ptr = &timerid;
+    (void) timer_create(CLOCKID, &sev, &timerid);
+
+    freq_nanosecs  = (long long)(timeout * 1000000000);
+    its.it_value.tv_sec  = freq_nanosecs / 1000000000;
+    its.it_value.tv_nsec = freq_nanosecs % 1000000000;
+    its.it_interval.tv_sec = 0;
+    its.it_interval.tv_nsec = 0;
+
+    (void) timer_settime(timerid, 0, &its, NULL);
+    connection_fd = fd;
+
+    res = _XReply (dpy, (xReply *)&rep, 0, xTrue);
+
+    connection_fd = -1;
+    (void) timer_delete(timerid);
+    pthread_sigmask(SIG_SETMASK, &origmask, NULL);
+    sigaction (CONN_SIG, &old_action, NULL);
+
+    UnlockDisplay(dpy);
+    SyncHandle();
+    return (int)res;
+}
+
+int check_frame_connection(struct frame * frame, double timeout)
+{
+    block_input ();
+    int fd = ConnectionNumber (FRAME_X_DISPLAY (frame));
+    int res = XCheckConnection (
+        FRAME_X_DISPLAY (frame), FRAME_OUTER_WINDOW (frame), fd, timeout);
+    unblock_input ();
+    return res;
+}
+
+DEFUN ("x-check-frame", Fx_check_frame,
+       Sx_check_frame, 1, 1, 0,
+       doc: /* check the connection with the display of the given frame.  */)
+  (Lisp_Object f)
+{
+    if (!f)
+        return Qnil;
+
+    if (NILP (f))
+        return Qnil;
+
+    if (Fframep(f) != Qx)
+        return Qnil;
+
+    if (!FLOATP (Vx_check_frame_timeout))
+        return Qnil;
+
+    /* Default timeout is 0.5 second. This timeout will occur
+       only when the libx11 did not noticed the frame was
+       disconnected. */
+    double timeout = XFLOAT_DATA (Vx_check_frame_timeout);
+
+    struct frame *frame = XFRAME (f);
+    int ret = check_frame_connection (frame, timeout);
+    return ret ? Qt : Qnil;
+}
+
+
+
 /* Flush display of frame F.  */
 
 static void
@@ -13747,4 +13641,11 @@ syms_of_xterm (void)
 consuming frame position adjustments.  In newer versions of GTK, Emacs
 always uses gtk_window_move and ignores the value of this variable.  */);
   x_gtk_use_window_move = true;
+
+  defsubr (&Sx_check_frame);
+
+  DEFVAR_LISP ("x-check-frame-timeout", Vx_check_frame_timeout,
+    doc: /* How long to wait a display to response. */);
+  Vx_check_frame_timeout = make_float (0.5);
+
 }