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List:       freedesktop-xorg
Subject:    =?gb2312?B?tPC4tDogQSBxdWVzdGlvbiBhYm91dCBYT3BlbkRpc3BsYXkgZmFpbA==?=
From:       "Ma, Qingyu (GE Healthcare)" <Qingyu.Ma () ge ! com>
Date:       2010-04-28 11:34:36
Message-ID: 64E1EBED52686A4189F71097E6E908AC07CBDAA6 () SHAMLVEM03 ! e2k ! ad ! ge ! com
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Thanks for your reply.

My process is executed in a script which is executed by another process. The script \
is like:

export DISPLAY=:0.1
./myProcess & 
export  DISPLAY=:0.0

I know when myProcess opens display, current DISPLAY maybe changed back to :0.0.  \
It's another issue. But till now, myProcess is displayed on :0.1 each time. Of \
course, I'm not sure if myProcess try to open display at the right point of changing \
DISPLAY, whether it can get a valid display (0 or 1)?

Is there any other possibility to cause XOpenDisplay fail, like network, IP stack or \
anything?


Best Regards,
Ma Qingyu

-----ÓʼþÔ­¼þ-----
·¢¼þÈË: Peter Hutterer [mailto:peter.hutterer@who-t.net] 
·¢ËÍʱ¼ä: 2010Äê4Ô 28ÈÕ 19:18
ÊÕ¼þÈË: Ma, Qingyu (GE Healthcare)
³­ËÍ: xorg@lists.freedesktop.org
Ö÷Ìâ: Re: A question about XOpenDisplay fail

On Wed, Apr 28, 2010 at 02:50:50PM +0800, Ma, Qingyu (GE Healthcare) wrote:
> Hello,
> 
> During my developing work, I meet a problem about XOpenDisplay. Could 
> you please give me some consult?

please don't cross-post. taking xorg-devel off the CC list.
 
> I'm developing a system, which uses fvwm as WM. Two fvwm are executed 
> to implement two separated screens. My process is displayed on one 
> screen(DISPLAY). It calls XOpenDisplay(NULL) to get one Display 
> connection to be used as display image, and another Display to be used 
> as toggle keyboard led (whenever keyboard led state is changed, a new 
> Display is opened and closed). The function is OK. But when I was 
> doing monkey and cycle test, there is a very very little possibility 
> that my process may crash. I looked through my code, and found a bug 
> which was that I didn't check the return value of XOpenDisplay, and 
> use it directly . I have checked that a NULL Display will cause 
> process crash in following code. It's just my analysis and guess, I'm 
> not sure whether it does be the root cause. And, by now, the cycle and 
> monkey cannot re-occur the issue.
> 
> So, I want to get some information from you to help to reach the root 
> cause. What will cause XOpenDisplay return NULL? How can I simulate 
> the case?(When my process is executed, I'm sure the XWindow and fvwm 
> have been booted up.)

XOpenDisplay on an invalid display will return NULL. so you can either specify an \
invalid display in the code directly or through your DISPLAY environment variable.

DISPLAY=:10 your-program-name

should fail, unless you really have an X server on display 10 which is rather \
unlikely.

Cheers,
  Peter
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