NEWS.md
In shard: Deterministic, Zero-Copy Parallel Execution for R

shard 0.2.0

Internal performance and correctness refactor. No user-facing API was removed; apart from a new path= argument to as_shared() and the deprecation of the unused pool_create(heartbeat_interval=), all changes improve the behavior, speed, or robustness of the existing runtime.

Overhauled the task-dispatch core: the worker function and diagnostics setup are now exported once per dispatch instead of per task, and run-level diagnostics are gated behind diagnostics = TRUE. This sharply reduces dispatch wall-clock and task-payload size on many-shard workloads.
The internal task queue uses an O(1) claim cursor with batched claims.
Non-contiguous (strided) shard index sets are compacted on the wire and reconstructed in the worker, cutting serialization cost for sparse selections.
On Linux, backing = "auto" now maps shared memory on tmpfs; added madvise() access hints and a cached segment base pointer.
Buffer sparse (non-contiguous) reads and writes use typed C gather/scatter instead of a full read-modify-write, while bulk contiguous sub-block writes keep their fast path.
Contiguous buffer reads (buf[], as.vector(buf), per-shard slice reads) now use a single typed C read instead of a raw intermediate plus readBin(), halving allocation and copy volume when materializing results.
Master-side chunk-queue management is O(1) per chunk (cursor-based dequeue, preallocated completion storage); completed chunks retain only minimal metadata by default, releasing shard descriptors as the run progresses.
Worker liveness probes reuse a ps handle cached at spawn time (also more robust against PID reuse) instead of creating one per check per poll tick.
Buffer index validation and contiguity detection are allocation-free and preserve ALTREP-compact index ranges.
Indexing a buffer with 3 or more dimensions now gathers/scatters only the selection instead of materializing the whole buffer; array assignment no longer breaks the lock-free disjoint parallel-write guarantee.
The online autotuner and stream_map() no longer grow result lists incrementally across phases/partitions.

seed= now installs an independent per-shard L'Ecuyer-CMRG RNG stream immediately before each shard runs, so results are identical regardless of workers, chunk_size, or shard-to-worker assignment, and are stable across worker recycling and restarts.
cow = "deny" is enforced for shared inputs at the R level; deep-environment validation for shared objects is preserved.
C layer: corrected long-vector handling (XLENGTH), Windows read-only segment protection, and copy/coercion accounting.
view_col_vars() and the col_vars kernel use a numerically stable (Welford) computation.
shard_map() validates borrow/out names against the worker function's formals before creating the pool, failing fast with a clearer message.
shard_reduce(): minimal reducer environment, per-shard seed streams, and corrected automatic chunking and init semantics.
Worker recycling replays a bootstrap manifest so borrowed inputs and outputs are correctly re-exported to restarted workers.
Fixed an integer overflow that broke share() for atomic vectors over 2GB (about 269 million doubles).
Fixed shard_reduce() receiving a stale output-buffer handle when run after shard_map() on the same pool with a same-named out= buffer.
C layer hardening: shared-memory offset/length validation is overflow-safe (negative or non-finite values now error cleanly instead of reading or writing out of bounds), freshly created ALTREP objects are protected from garbage collection during construction, shard ALTREP methods no longer misidentify other packages' ALTREP objects, and the shared task queue validates its header before use.
table_write() validates shard_id, so an NA id can no longer produce a part file that table_finalize() silently drops.
Fixed row_layout() erroring when a trailing shard has zero rows, and shard_crossprod() failing on matrices with fewer than 8 columns.
Worker liveness detection no longer reports dead workers as alive on systems without the ps package.
On macOS, the "shm" backing now works: generated segment names previously exceeded the Darwin name-length limit, so shm_open() always failed.
shard_map(health_check_interval=) is honoured when supplied explicitly (profile presets no longer override it), and share(name=) now applies to fast-path atomic shares. pool_create(heartbeat_interval=) is deprecated: it was never consulted (health checks are per-chunk, not time-based).

autotune_block_size() now clamps correctly to max_shards_per_worker and warns when a scratch budget would require more shards than allowed.
The default worker count can be overridden with options(shard.workers = N) or the SHARD_WORKERS environment variable (still capped to 2 under R CMD check).

Substantially expanded unit-test coverage of buffers, views, tables, kernels, and internal helpers.

shard 0.1.1

Fixed a gcc-UBSAN report: the task-queue header used a C89 tasks[1] trailing-array idiom; changed to a C99 flexible array member.
Default worker counts now respect _R_CHECK_LIMIT_CORES_ and are capped at 2 during R CMD check, at all call sites (pool_create(), shard_map(), shards(), shard_reduce()).