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神经网络昆斯林的新闻组分类2006

Path: cantaloupe.srv.cs.cmu.edu!das-news.harvard.edu!ogicse!decwrl!uunet!world!oj
From: [e-mail] (Oliver Jones)
Newsgroups: comp.windows.x
Subject: Re: Q: How to avoid XOpenDisplay hang?
Keywords: Xlib
Message-ID: <[e-mail]>
Date: 6 Apr 93 22:03:33 GMT
Article-I.D.: world.C531A0.M3I
References: <[e-mail]>
Organization: Shawsheen Software
Lines: 18

In article <[e-mail]> [e-mail] writes:
>I'm writing 'xwall', a simple X version of 'wall', and I want it to
>put a message up on each of a default list of displays.  The problem
>is that XOpenDisplay hangs if one of the displays is currently
>controlled by xdm (login screen). 

xdm does XGrabServer when it's running in secure mode (so do some
screen-locks).  There's really no simple way to tell this is the case.

You can take xdm out of secure mode;  probably not too cool.

You can wrap your call to XOpenDisplay in some code which solicts
a future SIGALRM and longjmps past the XOpenDisplay from the signal
handler.  An example of this can be seen in the xdm sources.

Note that longjmping out of XOpenDisplay probably causes a memory
leak;  any program functioning this way probably needs to exit() 
regularly.