[Bug libstdc++/94160] std::pmr::pool_options::max_blocks_per_chunk=1 causes pool resources to return null pointers

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94160

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:30b41cfbb2dade63e52465234a725d1d02fe70aa

commit r11-3102-g30b41cfbb2dade63e52465234a725d1d02fe70aa
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Sep 10 15:39:15 2020 +0100

    libstdc++: handle small max_blocks_per_chunk in pool resources [PR 94160]

    When a pool resource is constructed with max_blocks_per_chunk=1 it ends
    up creating a pool with blocks_per_chunk=0 which means it never
    allocates anything. Instead it returns null pointers, which should be
    impossible.

    To avoid this problem, round the max_blocks_per_chunk value to a
    multiple of four, so it's never smaller than four.

    libstdc++-v3/ChangeLog:

            PR libstdc++/94160
            * src/c++17/memory_resource.cc (munge_options): Round
            max_blocks_per_chunk to a multiple of four.
            (__pool_resource::_M_alloc_pools()): Simplify slightly.
            * testsuite/20_util/unsynchronized_pool_resource/allocate.cc:
            Check that valid pointers are returned when small values are
            used for max_blocks_per_chunk.