rts-alloc

rts-alloc provides an shared memory Allocator for use in sharing allocations between processes. The allocator is a lock-free slab allocator. It is meant for allocating small objects quickly and is NOT meant for use as a general purpose allocator.

There is a maximum number of "workers" (thread/process) that may use the allocator at any given time. Each worker must be assigned a unique id when creating or joining the allocator space.

When a worker allocates memory, it must have an owned slab within the shared memory space. Each slab is divided into "slots" of memory for given size classes (see size_classes.rs). When a worker allocates memory, it will first try to allocate in slabs it already owns. If there are no suitable slots in owned slabs, it will try to take a slab from the global pool. Since all workers pull and push to this global pool, it is a source of contention - and should be avoided whenever possible. Once popped from the global pool, the slab is owned by the worker and is assigned to a specific size class.

When a worker frees allocations it created itself, the newly freed slot of memory within the slab is immediately returned and made available for reuse by the same worker. When a worker frees allocations created by another worker, the slot is added to a free list which will only become available for reuse by the worker that owns the corresponding slab cleans its remote free lists. There is some contention when cleaning these free lists, in finding the initial head of the list, so this should be done as infrequently as possible. Of course, the worker also does not want to clean so infrequently that it runs out of available memory space.

When the owning worker has freed all slots within an owned slab, it must return the slab! [^1]

[^1]: or suffer my curse