Comment 1 for bug 965798

Allow me to copy my analysis of this bug here
from https://jogamp.org/bugzilla/show_bug.cgi?id=566#c13

This bug affects all Mesa8 w/ the tls_model("global-dynamic") patch enabled!

+++

Analysis of patch 113_fix_tls.diff and it's freezing impact:

+++
 extern __thread void *u_current_user
- __attribute__((tls_model("initial-exec")));
+ __attribute__((tls_model("global-dynamic")));
+++

the above changes the TLS behavior of libGL.

Note: u_current_user reflects the current context
changed by glXMakeContextCurrent(..).

Phenomenon of AWT-EDT glXMakeContextCurrent() freeze:

[0] Java launches
[0.1] starts new AWT-EDT thread
[0.2] starts main thread and hands over execution of main

[1] JOGL loads and initializes the libGL via 1st call of GLProfile.initSingleton()
incl. lib loading via dlopen() and symbol lookup etc.

[2] Step [1] kicks of the shared resource runner, which creates the very 1st
JOGL GL context while probing all profiles.

[3] At some point, AWT-EDT runs a JOGL Runnable:
[3.1] ctx = createContext()
[3.2] makeCurrent(dpy, read, write, ctx);
[3.3] makeCurrent(dpy, 0, 0, 0); -> release context *** Freeze ***

glx/glxcurrent.c/MakeContextCurrent():............__glXSetCurrentContextNull()
glx/glxcurrent.c/__glXSetCurrentContextNull(): .........._glapi_set_context(NULL);
./mapi/mapi/mapi_glapi.c/_glapi_set_context(NULL):........u_current_set_user(NULL);
./mapi/mapi/u_current.c/u_current_set_user(NULL):.............u_current_init();
./mapi/mapi/u_current.c/u_current_set_user(NULL): .............u_current_user =(void *) ptr; ***** FREEZE ***

Mesa8 release-context implementation attempts to access the TLS u_current_user 'field'.

For some reason, an already existing thread like AWT-EDT [0.1] cannot use libGL's global TLS [3]
when the latter was initialized by a later running thread [0.2] + [1].

Prove that this is the root cause can be made by it's remedies:

R1: Set java system property 'sun.java2d.opengl' to 'true', which loads and
uses libGL from the start.

R2: Load the libraries [1] from the AWT-EDT

+++

R2 is our workaround in JOGL and works fine w/ Ubuntu 12.04 & Mesa8

+++

Nevertheless, it is unclear whether the above behavior is intrinsic to
tls_model("global-dynamic") and hence a restriction or other special
circumstances
lead to an erroneous behavior.

Note:tls_model("initial-exec") works fine, i.e. w/o patch 113_fix_tls.diff