Arena_activator</a>&lt;A1&gt;</code> operates completely independently from <code><a class="el" href="classipc_1_1shm_1_1stl_1_1Arena__activator.html" title="RAII-style class operating a stack-like notion of a the given thread&#39;s currently active SHM-aware Are...">Arena_activator</a>&lt;A2&gt;</code>, even in the same thread, if <code>A1</code> is not same-as <code>A2</code>. So any "clash" would only occur (1) in a given thread, not across threads; (2) for a given SHM provider type, not across 2+ such t