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156d79cef0
The block iterator requires access to a bunch of data from the
underlying `reftable_block` that it is iterating over. This data is
stored by copying over relevant data into a separate set of variables.
This has multiple downsides:
- We require more storage space than necessary. This is more of a
theoretical issue as we shouldn't ever have many blocks.
- We have to perform more bookkeeping, and the variable names are
inconsistent across the two data structures. This can lead to some
confusion.
- The lifetime of the block iterator is tied to the block anyway, but
we hide that a bit by only storing pointers pointing into the block.
There isn't really any good reason why we rip out parts of the block
instead of storing a pointer to the block itself.
Refactor the code to do so. Despite being simpler, it also allows us to
decouple the lifetime of the block iterator from seeking in a subsequent
commit.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
105 lines
2.9 KiB
C
105 lines
2.9 KiB
C
/*
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* Copyright 2020 Google LLC
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*
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* Use of this source code is governed by a BSD-style
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* license that can be found in the LICENSE file or at
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* https://developers.google.com/open-source/licenses/bsd
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*/
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#ifndef BLOCK_H
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#define BLOCK_H
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#include "basics.h"
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#include "record.h"
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#include "reftable-block.h"
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#include "reftable-blocksource.h"
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/*
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* Writes reftable blocks. The block_writer is reused across blocks to minimize
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* allocation overhead.
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*/
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struct block_writer {
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struct z_stream_s *zstream;
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unsigned char *compressed;
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size_t compressed_cap;
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uint8_t *block;
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uint32_t block_size;
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/* Offset of the global header. Nonzero in the first block only. */
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uint32_t header_off;
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/* How often to restart keys. */
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uint16_t restart_interval;
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uint32_t hash_size;
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/* Offset of next uint8_t to write. */
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uint32_t next;
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uint32_t *restarts;
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uint32_t restart_len;
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uint32_t restart_cap;
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struct reftable_buf last_key;
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/* Scratch buffer used to avoid allocations. */
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struct reftable_buf scratch;
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int entries;
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};
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/*
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* initializes the blockwriter to write `typ` entries, using `block` as temporary
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* storage. `block` is not owned by the block_writer. */
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int block_writer_init(struct block_writer *bw, uint8_t typ, uint8_t *block,
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uint32_t block_size, uint32_t header_off, uint32_t hash_size);
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/* returns the block type (eg. 'r' for ref records. */
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uint8_t block_writer_type(struct block_writer *bw);
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/* appends the record, or -1 if it doesn't fit. */
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int block_writer_add(struct block_writer *w, struct reftable_record *rec);
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/* appends the key restarts, and compress the block if necessary. */
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int block_writer_finish(struct block_writer *w);
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/* clears out internally allocated block_writer members. */
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void block_writer_release(struct block_writer *bw);
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/* Iterate over entries in a block */
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struct block_iter {
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/* offset within the block of the next entry to read. */
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uint32_t next_off;
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const struct reftable_block *block;
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/* key for last entry we read. */
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struct reftable_buf last_key;
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struct reftable_buf scratch;
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};
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#define BLOCK_ITER_INIT { \
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.last_key = REFTABLE_BUF_INIT, \
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.scratch = REFTABLE_BUF_INIT, \
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}
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/* Position `it` at start of the block */
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void block_iter_seek_start(struct block_iter *it, const struct reftable_block *block);
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/* Position `it` to the `want` key in the block */
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int block_iter_seek_key(struct block_iter *it, const struct reftable_block *block,
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struct reftable_buf *want);
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/* return < 0 for error, 0 for OK, > 0 for EOF. */
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int block_iter_next(struct block_iter *it, struct reftable_record *rec);
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/* Reset the block iterator to pristine state without releasing its memory. */
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void block_iter_reset(struct block_iter *it);
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/* deallocate memory for `it`. The block reader and its block is left intact. */
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void block_iter_close(struct block_iter *it);
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/* size of file header, depending on format version */
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size_t header_size(int version);
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/* size of file footer, depending on format version */
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size_t footer_size(int version);
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#endif
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