Long-standing error in exception handling by pool_allocator (contains untested patch)
Dhruv Matani
dhruvbird@gmx.net
Sun Oct 10 17:55:00 GMT 2004
Hi,
I guess this patch(attached) would be more in keeping with the original
spirit of the allocator. ChangeLog would of course remain unchanged.
If you remember, I had earlier mentioned something to this effect, but
then forgot totally about it!
http://gcc.gnu.org/ml/libstdc++/2004-03/msg00290.html
http://gcc.gnu.org/ml/libstdc++/2004-03/msg00288.html
-Dhruv.
On Sun, 2004-10-10 at 20:55, Paolo Carlini wrote:
> Paolo Carlini wrote:
>
> > Therefore, my plan would be preparing a simple testcase from your
> > complete
> > analysis, regression test the slighlty tweaked version, and repost it
> > to the list
> > for final review.
>
> The below is what I have just finished regtesting on x86/x86_64-linux.
> As you
> can see, I simply test that the fall back machinery originally designed
> by SGI/HP
> is actually working, instead of testing for memory corruption: the
> latter is more
> tricky, depends on too many parameters and risk to convey the misleading
> impression that the patch is "only" about memory corruption: in that
> case simply
> zeroing _S_start_free/_S_end_free before calling ::operator new would
> suffice.
>
> I'll wait until tomorrow in case of comments...
>
> Paolo.
>
> ////////////////
>
> ______________________________________________________________________
>
> 2004-10-11 Joachim Kuebart <kuebart@mathematik.uni-ulm.de>
> Paolo Carlini <pcarlini@suse.de>
>
> * src/pool_allocator.cc (__pool_alloc_base::_M_allocate_chunk):
> Deal properly with exceptions thrown by ::operator new(size_t).
> * testsuite/ext/pool_allocator/allocate_chunk.cc: New.
>
> * include/ext/pool_allocator.h: Include <cstdlib>.
>
> ______________________________________________________________________
>
> diff -urN libstdc++-v3-orig/include/ext/pool_allocator.h libstdc++-v3/include/ext/pool_allocator.h
> --- libstdc++-v3-orig/include/ext/pool_allocator.h 2004-08-30 20:22:01.000000000 +0200
> +++ libstdc++-v3/include/ext/pool_allocator.h 2004-10-10 15:38:38.000000000 +0200
> @@ -48,6 +48,7 @@
> #define _POOL_ALLOCATOR_H 1
>
> #include <bits/c++config.h>
> +#include <cstdlib>
> #include <new>
> #include <bits/functexcept.h>
> #include <bits/atomicity.h>
> diff -urN libstdc++-v3-orig/src/pool_allocator.cc libstdc++-v3/src/pool_allocator.cc
> --- libstdc++-v3-orig/src/pool_allocator.cc 2004-09-02 00:16:58.000000000 +0200
> +++ libstdc++-v3/src/pool_allocator.cc 2004-10-10 11:16:23.000000000 +0200
> @@ -90,8 +90,11 @@
>
> size_t __bytes_to_get = (2 * __total_bytes
> + _M_round_up(_S_heap_size >> 4));
> - _S_start_free = static_cast<char*>(::operator new(__bytes_to_get));
> - if (_S_start_free == 0)
> + try
> + {
> + _S_start_free = static_cast<char*>(::operator new(__bytes_to_get));
> + }
> + catch (...)
> {
> // Try to make do with what we have. That can't hurt. We
> // do not try smaller requests, since that tends to result
> @@ -111,11 +114,9 @@
> // right free list.
> }
> }
> - _S_end_free = 0; // In case of exception.
> -
> - // This should either throw an exception or remedy the situation.
> - // Thus we assume it succeeded.
> - _S_start_free = static_cast<char*>(::operator new(__bytes_to_get));
> + // what we have wasn't enough. Rethrow.
> + _S_start_free = _S_end_free = 0; // we have no chunk
> + __throw_exception_again;
> }
> _S_heap_size += __bytes_to_get;
> _S_end_free = _S_start_free + __bytes_to_get;
> diff -urN libstdc++-v3-orig/testsuite/ext/pool_allocator/allocate_chunk.cc libstdc++-v3/testsuite/ext/pool_allocator/allocate_chunk.cc
> --- libstdc++-v3-orig/testsuite/ext/pool_allocator/allocate_chunk.cc 1970-01-01 01:00:00.000000000 +0100
> +++ libstdc++-v3/testsuite/ext/pool_allocator/allocate_chunk.cc 2004-10-10 17:12:24.000000000 +0200
> @@ -0,0 +1,63 @@
> +// 2004-10-10 Paolo Carlini <pcarlini@suse.de>
> +
> +// Copyright (C) 2004 Free Software Foundation, Inc.
> +//
> +// This file is part of the GNU ISO C++ Library. This library is free
> +// software; you can redistribute it and/or modify it under the
> +// terms of the GNU General Public License as published by the
> +// Free Software Foundation; either version 2, or (at your option)
> +// any later version.
> +//
> +// This library is distributed in the hope that it will be useful,
> +// but WITHOUT ANY WARRANTY; without even the implied warranty of
> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +// GNU General Public License for more details.
> +//
> +// You should have received a copy of the GNU General Public License along
> +// with this library; see the file COPYING. If not, write to the Free
> +// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
> +// USA.
> +
> +// 20.4.1.1 allocator members
> +
> +#include <ext/pool_allocator.h>
> +
> +struct small
> +{
> + char c[16];
> +};
> +
> +struct big
> +{
> + char c[64];
> +};
> +
> +void*
> +operator new(size_t n) throw(std::bad_alloc)
> +{
> + static bool first = true;
> + if (!first)
> + throw std::bad_alloc();
> + first = false;
> + return std::malloc(n);
> +}
> +
> +// http://gcc.gnu.org/ml/libstdc++/2004-10/msg00098.html
> +void test01()
> +{
> + using __gnu_cxx::__pool_alloc;
> +
> + __pool_alloc<big> alloc_big;
> + alloc_big.allocate(1);
> +
> + // The constant 20 comes from __pool_alloc_base::_M_refill. See
> + // also __pool_alloc_base::_M_allocate_chunk.
> + __pool_alloc<small> alloc_small;
> + for (int i = 0; i < 20 * sizeof(big) / sizeof(small) + 1; ++i)
> + alloc_small.allocate(1);
> +}
> +
> +int main()
> +{
> + test01();
> +}
--
-Dhruv Matani.
http://www.geocities.com/dhruvbird/
The price of freedom is responsibility, but it's a bargain, because
freedom is priceless. ~ Hugh Downs
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