[This is from the Xt FAQ. I believe as long as XtCloseDisplay() is called and you don't return from the error handler, Xlib and Xt will handle the problem] The difficulty arises because the Xlib design presumed that an I/O error is always unrecoverable and so fatal. This is essentially true for a single display X based application, but not true for a multiple display program or an application that does things other than display information on an X server. When an X I/O error occurs the I/O error handler is called and _if_ it returns then an exit() happens. The only way around this is to use setjmp/longjmp to avoid returning to the I/O error handler. The following code fragment demonstrates this: #include <setjmp.h> jmp_buf XIOrecover; void XIOHandler (dpy) Display *dpy; { destroyDisplay (dpy); longjmp (XIOrecover, 1); } main () { ... if (setjmp (XIOrecover) == 0) XSetIOErrorHandler (XIOHandler); XtAppMainLoop (app_context); } The destroyDisplay() is something that given a Display pointer can go back to the application specific data and perform any necessary cleanup. It should also call XtCloseDisplay(). For those of you unfamiliar with setjmp/longjmp, when setjmp() is first called it returns a 0 and save's enough information in the jmp_buf that a latter execution of longjmp() can return the program to the same state as if the setjmp() was just executed. The return value of this second setjmp() is the value of the second argument to longjmp(). There are several caveats about using these but for this purpose it is adequate. Some other problems you might run into are resource converters that improperly cache resources. The most likely symptoms are Xlib errors such as BadColor, BadAtom, or BadFont. There may be problems with the total number of displays you can open since typically only a limited number of file descriptors are available with 32 being a typical value. You may also run into authorization problems when trying to connect to a display. There was much discussion in comp.windows.x about this topic in November of 91. Robert Scheifler posted an article which basically said this is the way it will be and Xlib will not change.