[Boost-bugs] [Boost C++ Libraries] #5673: Quick allocator error in multi thread

Subject: [Boost-bugs] [Boost C++ Libraries] #5673: Quick allocator error in multi thread
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-07-06 12:48:01

#5673: Quick allocator error in multi thread
----------------------------------------------------+-----------------------
 Reporter:  Yury Podpruzhnikov <QWERTYura@…>        |       Owner:         
     Type:  Bugs                                    |      Status:  new    
Milestone:  To Be Determined                        |   Component:  None   
  Version:  Boost 1.44.0                            |    Severity:  Problem
 Keywords:                                          |  
----------------------------------------------------+-----------------------
 Compiler: '''MSVS 2008'''
 use macros '''BOOST_SP_USE_QUICK_ALLOCATOR'''

 Exception (Access vialation by reading address) occured by constructor of
 '''shared_ptr'''.

 Cause of exception is multi thread creation of static mutex in quick
 allocator.

 shared_ptr call quick allocator.
 quick allocator use next code:
 {{{
 lightweight_mutex::scoped_lock lock( mutex() );
 }}}

 function '''mutex()''' return internal static variable:
 {{{
 boost_1_44_0\boost\smart_ptr\detail\quick_allocator.hpp
 template<unsigned size, unsigned align_> struct allocator_impl
 {
 ...

      static lightweight_mutex & mutex()
      {
          static freeblock< sizeof( lightweight_mutex ),
 boost::alignment_of< lightweight_mutex >::value > fbm;
          static lightweight_mutex * pm = new( &fbm ) lightweight_mutex;
          return *pm;
      }

 ...
 }
 }}}
 2 thread call mutex() (first time for this instantiation of template class
 allocator_impl). One start init '''pm''' and go to sleep. Other check that
 '''pm''' is initialized and return its value (in my case NULL) and raise
 exception.
 [[BR]]
 Initialization of static variable in C++ is not safe for multi thread.
 This code is incorrect. In dependence from realization of static variable
 you will be have access vialation or memory leak - flag of static variable
 initialization (construction) set before or after initialization.
 [[BR]]
 In MSVS 2008 flag set before and you take access vialation.
 [[BR]][[BR]]
 '''Decision''' [[BR]]
 Not resolve, but minimize problem. [[BR]]
 Idea:[[BR]]
 As I understand, This problem can appear in first initialization of
 __every__ instantiation of shared_ptr - first use __every__ instantiation
 of allocator_impl.
 [[BR]]
 If you synchronize of initialization '''pm''' then problem can appear only
 first initialization of __any__ instantiation of shared_ptr. And I can
 create first fictive shared_ptr in non-multi thread and then normal use
 shared_ptr in multi thread.
 [[BR]]
 Realization:[[BR]]
 {{{
 boost_1_44_0\boost\smart_ptr\detail\quick_allocator.hpp

 lightweight_mutex & global_mutex()
 {
    static freeblock< sizeof( lightweight_mutex ), boost::alignment_of<
 lightweight_mutex >::value > fbm;
     static lightweight_mutex * pm = new( &fbm ) lightweight_mutex;
          return *pm;
 }



 template<unsigned size, unsigned align_> struct allocator_impl
 {
      static lightweight_mutex & mutex()
      {
          static freeblock< sizeof( lightweight_mutex ),
 boost::alignment_of< lightweight_mutex >::value > fbm;
          static lightweight_mutex * pm = NULL;
          if(pm == NULL)
          {
             lightweight_mutex::scoped_lock lock( global_mutex() );
             if(pm == NULL)
             {
                 pm = new( &fbm ) lightweight_mutex;
             }
          }
          return *pm;
      }
 }
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5673>
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