swq_op_registrar class is not thread-safe

[Even Rouault]

The following sequence in swq_op_registrar::GetOperator() that is not protected by a mutex cause thread-safety issue.

    if( !papoOperations )
        Initialize();

The issue is that Initialize() can set a non-NULL papoOperations pointer while it is partially initialized.

Issue discovered with the enhancement of test_ogrsf to test thread-safety of OGR drivers that can be frequently reproduced

Two possible ways of fixing this :

• removing the test in the above snippet.
• or making Initialize() smarter to only set papoOperations when it is fully initialized. The difficulty here is to have the guarantee of a full memory barrier to avoid early assignement visibility.

Going for the easy and safe way...

[Even Rouault]

Fixed in trunk (r26312) and branches/1.10 (r26313)