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dshash: revise sequential scan support.

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The previous coding of dshash_seq_next(), on the first call, accessed
status->hash_table->size_log2 without holding a partition lock and without
guaranteeing that ensure_valid_bucket_pointers() had ever been called.

That oversight turns out to not have immediately visible effects, because
bucket 0 is always in partition 0, and ensure_valid_bucket_pointers() was
called after acquiring the partition lock.  However,
PARTITION_FOR_BUCKET_INDEX() with a size_log2 of 0 ends up triggering formally
undefined behaviour.

Simplify by accessing partition 0, without using PARTITION_FOR_BUCKET_INDEX().

While at it, remove dshash_get_current(), there is no convincing use
case. Also polish a few comments.

Author: Andres Freund <andres@anarazel.de>
Reviewed-By: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://postgr.es/m/CA+hUKGL9hY_VY=+oUK+Gc1iSRx-Ls5qeYJ6q=dQVZnT3R63Taw@mail.gmail.com
This commit is contained in:
Andres Freund
2022-04-04 14:32:52 -07:00
parent 55e566fc4b
commit 909eebf27b
2 changed files with 28 additions and 31 deletions
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src/include/lib/dshash.h
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@@ -101,7 +101,6 @@ extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
extern void *dshash_seq_next(dshash_seq_status *status);
extern void dshash_seq_term(dshash_seq_status *status);
extern void dshash_delete_current(dshash_seq_status *status);
extern void *dshash_get_current(dshash_seq_status *status);
/* Convenience hash and compare functions wrapping memcmp and tag_hash. */
extern int dshash_memcmp(const void *a, const void *b, size_t size, void *arg);