shared_promise::get_shared_future() is marked noexcept, but can
allocate memory. It is invoked by sstable partition index cache inside
an allocating section, which means that allocations can throw
bad_alloc even though there is memory to reclaim, so under normal
conditions.
Fix by allocating the shared_promise in a stable memory, in the
standard allocator via lw_shared_ptr<>, so that it can be accessed outside
allocating section.
Fixes#9666
Tests:
- build/dev/test/boost/sstable_partition_index_cache_test
Message-Id: <20211122165100.1606854-1-tgrabiec@scylladb.com>
1d84bc6c3b