libstdc++/5432: Implementation still not thread-safe on multiprocessor machines

[ljrittle@gcc.gnu.org]

Synopsis: Implementation still not thread-safe on multiprocessor machines

State-Changed-From-To: analyzed->feedback
State-Changed-By: ljrittle
State-Changed-When: Thu Jan 24 13:25:59 2002
State-Changed-Why:
    Andrew, there were two minor issues with your patch:
    (And it took collective thought to figure all this out
    so don't feel bad. ;-)
    
    In general, static _Atomic_word should always be init'd
    to 0 with C++.  We think g++ follows the init order
    rules of C which are tighter than C++ but for C++
    non-zero static values may not be init'd until after main()
    has run (the only rule says it must be done "before
    the related block [scope] is entered" which might be after
    threads were started).
    
    Secondly:
    
    <       if (--_M_references == 0)  // XXX MT
    ---
    >       if (__exchange_and_add(&_M_references, -1) == 1)
    
    is correct (you had == 0).  I.e. assuming it was correct
    as written (other than thread-safety) your rewrite had a
    memory leak.
    
    Other than that, Nathan and I have reviewed the patch;
    I have tested it and installed it (that report to
    the libstdc++ mailing list).  To be closed after you
    confirm MP *-*-linux* system fixed as installed and
    then I move it to 3.0.X branch.  Thanks, Loren

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=5432