[Qt-interest] Create a new GUI Thread

[Thiago Macieira]

Luke Campagnola wrote:
>I thought that might be the case, but I'm pretty surprised by it--why
> should X11 care whether two windows are controlled by two separate
> processes or by two threads in the same process?

The X11 protocol and the X11 server don't care.

libX11.so, however, does. And there's where the problem lies.

That library was not designed when threads were common-place. It provides 
no locking primitives. And since the X11 operations must be serialised 
onto a socket (shared by all threads), if two threads try to send at the 
same time, there will be synchronisation problems.

Also note that the main thread will keep polling the X11 socket and 
popping events off its stack. So, an operation in another thread that 
requires sending and receiving from the X server also needs to make sure 
no other threads are waiting for data.

Like I said, that library has no such API. Its replacement (libxcb) does, 
but porting Qt to XCB would be no small task. Not to mention that XCB will 
probably not be present in the Unix systems that are not based on X.org.

Finally, you said your problem is that your GUI operations can't fit in 
one single core. I strongly urge you to reconsider your design: even if 
you can split it over two threads, you have to remember that there are 
people out there running systems with single cores, or people who run 
other busy programs on their systems.

-- 
Thiago Macieira - thiago.macieira (AT) nokia.com
  Senior Product Manager - Nokia, Qt Software
      Sandakerveien 116, NO-0402 Oslo, Norway
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