[Boost-bugs] [Boost C++ Libraries] #7066: Thread: An attempt to fix current_thread_tls_key static initialization order

Subject: [Boost-bugs] [Boost C++ Libraries] #7066: Thread: An attempt to fix current_thread_tls_key static initialization order
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-07-03 06:25:24

#7066: Thread: An attempt to fix current_thread_tls_key static initialization
order
-----------------------------------------------------------------------------------------+
 Reporter:  Pekka Seppänen <pekka.seppanen@…>                                            |       Owner:  anthonyw
     Type:  Bugs                                                                         |      Status:  new     
Milestone:  To Be Determined                                                             |   Component:  thread  
  Version:  Boost 1.50.0                                                                 |    Severity:  Problem 
 Keywords:  current_thread_tls_key set_current_thread_data current_thread_tls_init_flag  |  
-----------------------------------------------------------------------------------------+
 Currently Boost.Thread's Win32 TLS implementation uses a static variable
 (`thread::current_thread_tls_key`) that is not defined at a function
 scope.

 This has a certain shortcoming: As initilization order of global static
 variables is not predictable, it may happen that
 `thread::current_thread_tls_key` is used (via
 `thread::set_current_thread_data()`) before it is actually initialized by
 compiler (or the underlaying OS, to be precise). (An example: class that
 uses `thread_specific_ptr` and is not heap allocated.)

 Potentially any prior versions to Boost 1.50.0 are also affected, as
 1.50.0 merely changed the initial value from a zero to a non-zero value.

 A proposed solution is to move `thread::current_thread_tls_key` inside a
 function scope (inside a helper function that sole purpose is to return
 reference to that variable). This ensures that `current_thread_tls_key` is
 initiliazed properly before it's used for the first time. As
 `thread::set_current_thread_data()` uses a static
 `current_thread_tls_init_flag` Boost.Once flag that is currently
 initialized at a global scope, move that flag too inside a function scope.

 A patch that implements proposed solution is attached. Unfortunaly,
 currently no test case exists (not sure if one is too easy to be made; At
 least on MSVC9 global static variables are initialized before the
 program's entry point inside a simple loop).

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/7066>
Boost C++ Libraries <http://www.boost.org/>
Boost provides free peer-reviewed portable C++ source libraries.