Bug 435719

*Description of problem:

In the default colormap, pixel 0 refers to black
color(0,0,0). However, pixel 0 refers to the other color
after my customer did the following operation.

1. Set the color depth to 8bit on RHEL4

2.Run XAllocNamedColor( dsp, cmap, "black", &color, &exact )
 more than 32768 times, reference to black pixel shift to
 other pixel number that is not 0.

3. Runs XAllocNamedColor with other color, pink for example,
  RGB value of pixel 0 becomes the RGB value for pink. Thus
  pixel 0 released black(0,0,0). This will show pink where
  black should show in your screen.


*How reproducible:
Always.


*Steps to Reproduce:

The customer gave us the test program to reproduce this(See the attachment -
test_program.tar). Do the following.

1. Set the color depth to 8bit on RHEL4

2. Compile dumpcolor.c/allocblack.c/allocpink.c as follows.

  gcc dumpcolor.c -lX11 -L /usr/X11R6/lib -o dumpcolor
  gcc allocblack.c -lX11 -L /usr/X11R6/lib -o allocblack
  gcc allocpink.c -lX11 -L /usr/X11R6/lib -o allocpink

3. Start X with mwm window manager -> xinit -e mwm

4. Run ./dumpcolor :0.0 0

5. Run ./allocblack :0.0 40000
  -> At this stage, pixel 0 refers to the other pixel

6. Run ./allocpink :0.0
  -> RGB of pink is placed in pixel 0

7. Run ./dumpcolor to see that pixel 0 now refers to RGB of
  pink.


*Actual results:
pixel 0 refers to the other color.


*Expected results:
pixel 0 should refer to black color(0,0,0).


*Additional info:
This only occurs in color depth of 8bit.

We have posted this issue to xgl-devel and got the
following reply.

-------------------------------------------------------------
Subject:
Re: Pixel 0 shows RGB value thats are not black(0.0,0) with 8bit depth on RHEL4
From:
Adam Jackson <ajackson>
Date:
Tue, 26 Feb 2008 12:13:26 -0500
To:
xgl-devel
CC:
Kenji Suzuoki <ksuzuoki>

On Tue, 2008-02-26 at 17:51 +1000, Kenji Suzuoki wrote:
> > Hi there,
> >
> > A customer is asking if it is a X's bug that pixel 0 releases black
> > color(0,0,0) after certain condition.
> >
> > Setting color depth to 8bit on RHEL4, then run
> >
> > XAllocNamedColor( dsp, cmap, "black", &color, &exact ) ;
> >
> > more than 32768 times, reference to black pixel shift to other pixel
> > number that is not 0.
> >
> > After that if he runs XAllocNamedColor with other color, pink for
> > example, RGB value of pixel 0 becomes the RGB value for pink. Thus
> > pixel 0 released black(0,0,0).
> >
> > [ Questions ]
> > -----------------------------------------------------------------------
> > 1. Is this a bug ?

Yes.  Yes, very much so.

Colormap slots have reference counts, so that when the client holding
that slot dies, it releases any slots it was holding on to.  The
reference count happens to be a short int.  D'oh.  (Not even unsigned
short!  Oh man.)

> > 2. Does RHEL4 support 8bit depth ?

Yes.
-------------------------------------------------------------

*Attachment
sysreport - RHEL4UP4.tar.bz2
test program - test_program.tar
result - our test result using the test program