Whatever. Allocation is slow enough that I don't care about a noncontended lock. Make things work by default and if you want to gain performance by not allowing

Whatever. Allocation is slow enough that I don't care about a noncontended lock. Make things work by default and if you want to gain performance by not allowing multithreading then that should be possible and easy. But safety first, as in most cases it really don't matter. When it comes to mainstream general purpose allocators it isn't really a tradeoff anyhow, as all of them are nominally threadsafe. Even glibc claims to be multithreading safe even if it tends to not return or reuse all freed memory.