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

[andrew@andypo.net]

>Number:         5432
>Category:       libstdc++
>Synopsis:       Implementation still not thread-safe on multiprocessor machines
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Jan 19 07:26:00 PST 2002
>Closed-Date:
>Last-Modified:
>Originator:     andrew@andypo.net
>Release:        gcc-3.0.4-cvs-20020116
>Organization:
>Environment:
System: SunOS primo 5.6 Generic_105181-26 sun4u sparc SUNW,Ultra-4
Architecture: sun4configured with: /disks/nermal/andrewp/cvs/gcc-3_0-branch/configure --prefix=/opt/gcc-3.0.4-20020116-sparc-sun-solaris2.6-gnu-asld --with-gnu-as --with-gnu-ld --enable-threads=solaris --enable-version-specific-runtime-libs --disable-shared --enable-languages=c++
[ This is on a 4 processor machine ]

>Description:
[ Re libstdc++/5347 and libstdc++/5037 ]

In our project which is heavily multi-threaded we would occasionally get randon crashes which were associated with the iostreams code.

Managed to get it down to a very small test case which indicates the problems.

[ I'm also not sure that the file attachments have worked, I'm sending them to the gcc-mailing list as well.... ]
>How-To-Repeat:
Compile and run the attached program with gcc-3.0.x on a multiprocessor system (in this case UltraSparc/Solaris6, but similar things happen on a dual processor i686/Redhat7.2). Sometimes it will work, sometimes you will get a Bus Error and sometimes a Segmentation Fault

% /opt/gcc-3.0.4-20020116-sparc-sun-solaris2.6-gnu-asld/bin/g++ -g main.cxx -lpthread
% a.out
% a.out
% a.out
Bus error (core dumped)
% gdb a.out core
[...]
(gdb) where
#0  0x00020270 in std::__ctype_abstract_base<char>::widen(char) const ()
    at /disks/primo4/workplaces/andrewp/gnu/gcc-3.0.4-20020116-build/sparc-sun-solaris2.6/libstdc++-v3/include/bits/locale_facets.h:97
#1  0x0001fdd4 in std::basic_ios<char, std::char_traits<char> >::widen(char) const (this=0xef109ccc, __c=32 ' ')
    at /disks/primo4/workplaces/andrewp/gnu/gcc-3.0.4-20020116-build/sparc-sun-solaris2.6/libstdc++-v3/include/bits/locale_facets.h:97
#2  0x0001f850 in std::basic_ios<char, std::char_traits<char> >::init(std::basic_streambuf<char, std::char_traits<char> >*) (this=0xef109ccc, __sb=0x0)
    at /disks/primo4/workplaces/andrewp/gnu/gcc-3.0.4-20020116-build/sparc-sun-solaris2.6/libstdc++-v3/include/bits/basic_ios.tcc:125
#3  0x0001f918 in std::istream::istream(std::basic_streambuf<char, std::char_traits<char> >*) ()
    at /disks/primo4/workplaces/andrewp/gnu/gcc-3.0.4-20020116-build/sparc-sun-solaris2.6/libstdc++-v3/include/bits/std_istream.h:74
#4  0x0001f4e8 in std::iostream::iostream(std::basic_streambuf<char, std::char_traits<char> >*) (this=0xef109ccc, __vtt_parm=0x4be1c, __sb=0x0)
    at /disks/primo4/workplaces/andrewp/gnu/gcc-3.0.4-20020116-build/sparc-sun-solaris2.6/libstdc++-v3/include/bits/std_istream.h:274
#5  0x0001f318 in std::basic_stringstream<char, std::char_traits<char>, std::allocator<char> >::basic_stringstream(std::_Ios_Openmode) (this=0xef109c70, 
    __m=24)
    at /opt/gcc-3.0.4-20020116-sparc-sun-solaris2.6-gnu-asld/lib/gcc-lib/sparc-sun-solaris2.6/3.0.4/include/g++/bits/std_sstream.h:331
#6  0x000113ac in threadFunc () at main.cxx:11
(gdb) quit

% a.out
% a.out
% a.out
Segmentation fault (core dumped)
% gdb a.out core
[...]
(gdb) where
#0  0x00000000 in ?? ()
#1  0x00017678 in std::locale::facet::_M_remove_reference() (this=0x59d48)
    at /disks/nermal/andrewp/cvs/gcc-3_0-branch/libstdc++-v3/src/locale.cc:537
#2  0x00019c90 in std::locale::_Impl::~_Impl() (this=0x592d8)
    at /disks/primo4/workplaces/andrewp/gnu/gcc-3.0.4-20020116-build/sparc-sun-solaris2.6/libstdc++-v3/include/bits/stl_iterator.h:478
#3  0x00023fc4 in std::locale::_Impl::_M_remove_reference() (this=0x592d8)
    at /disks/primo4/workplaces/andrewp/gnu/gcc-3.0.4-20020116-build/sparc-sun-solaris2.6/libstdc++-v3/include/bits/localefwd.h:332
#4  0x00016fc0 in std::locale::operator=(std::locale const&) (this=0xef109d30, 
    __other=@0xef1099f8)
    at /disks/nermal/andrewp/cvs/gcc-3_0-branch/libstdc++-v3/src/locale.cc:406
#5  0x00016224 in std::ios_base::_M_init() (this=0xef109d30)
    at /disks/nermal/andrewp/cvs/gcc-3_0-branch/libstdc++-v3/src/ios.cc:267
#6  0x0001f824 in std::basic_ios<char, std::char_traits<char> >::init(std::basic_streambuf<char, std::char_traits<char> >*) (this=0xef109ccc, __sb=0x0)
    at /disks/primo4/workplaces/andrewp/gnu/gcc-3.0.4-20020116-build/sparc-sun-solaris2.6/libstdc++-v3/include/bits/basic_ios.tcc:122
#7  0x0001f918 in std::istream::istream(std::basic_streambuf<char, std::char_traits<char> >*) ()
    at /disks/primo4/workplaces/andrewp/gnu/gcc-3.0.4-20020116-build/sparc-sun-solaris2.6/libstdc++-v3/include/bits/std_istream.h:74
#8  0x0001f4e8 in std::iostream::iostream(std::basic_streambuf<char, std::char_traits<char> >*) (this=0xef109ccc, __vtt_parm=0x4be1c, __sb=0x0)
    at /disks/primo4/workplaces/andrewp/gnu/gcc-3.0.4-20020116-build/sparc-sun-solaris2.6/libstdc++-v3/include/bits/std_istream.h:274
#9  0x0001f318 in std::basic_stringstream<char, std::char_traits<char>, std::allocator<char> >::basic_stringstream(std::_Ios_Openmode) (this=0xef109c70, 
    __m=24)
    at /opt/gcc-3.0.4-20020116-sparc-sun-solaris2.6-gnu-asld/lib/gcc-lib/sparc-sun-solaris2.6/3.0.4/include/g++/bits/std_sstream.h:331
#10 0x000113ac in threadFunc () at main.cxx:11
(gdb) quit
>Fix:
With the attached patch, the attached program 'always' seems to work (I had it in a while loop running for about an hour...)

I don't make any guarantees for the correctness of the patch, but it definitely addresses some of the 'XXX MT' issues in the source code (eg using _Atomic_word, __atomic_add, __exchange_and_add and a lock)

The gcc-3.1 cvs code is very similar, if not the same...
>Release-Note:
>Audit-Trail:
>Unformatted:
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