XOpenDisplay call sequence

[Aaron Plattner]

On 11/28/2016 01:31 PM, Krzywicki, Alan wrote:
>
> So if I follow the XOpenDisplay sequence up the stack I see
> xcb_connect() / _/xcb_open/_abstract( ) trying to open
> “/tmp/.X11-unix/X0” with protocol set to 0.   On one system it
> eventually calls select(), on another it uses poll() instead, so it is
> looking for a response.  Once in a while it takes over a minute to get
> a response.   Can anyone describe a general overview of what it is
> trying to open?  Any idea why the select/poll call hangs so long?
>
>  
>
> Stack example:
>
>  
>
> #0  0xffffe424 in __kernel_vsyscall ()
> #1  0xb6ad657d in select () from /lib/i686/libc.so.6
> #2  0xb68997fc in ?? () from /usr/lib/libxcb.so.1
> #3  0xb68985db in xcb_connect_to_fd () from /usr/lib/libxcb.so.1
> #4  0xb689b6cd in xcb_connect () from /usr/lib/libxcb.so.1
> #5  0xb7004b9b in _XConnectXCB () from /usr/lib/libX11.so.6
> #6  0xb6fe5f10 in XOpenDisplay () from /usr/lib/libX11.so.6
> #7  0x0805f463 in main ()
>
>  
>
My guess is that the missing stack frames are

#2.0 read_block()
#2.1 _xcb_in_read_block()
#2.2 read_setup()

If that's where it's blocked, then it's waiting for the server to send
the setup block. Either the server is busy processing another client's
request, or some other client grabbed the server and hasn't ungrabbed it
yet. You'll have to debug the server to see whether it's stuck too or if
/ why it chose not to send the connection block.
>
>  
>
> / Alan K.
>
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