Concurrency

• get() and get_batch() are thread-safe. For method=1/2 a per-variable lock in DDStore::get() serializes calls on one variable (it guards shared receive state; without it concurrent calls crashed). Both release the GIL during the transfer.

• method=0 get_batch() is collective: every rank calls it the same number of times, in the same order, from one thread. vae-ddp.py therefore allows no worker threads with method=0.

• Only the main thread calls MPI (setup, epoch_begin/epoch_end, method=0 reads); mpi4py’s default MPI_THREAD_MULTIPLE is fine, FUNNELED is the minimum. If you call MPI from your own worker threads, keep MULTIPLE.