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This new interface allows us to enqueue some of the entries being checked out to later uncompress them, apply in-process filters, and write out the files in parallel. For now, the parallel checkout machinery is enabled by default and there is no user configuration, but run_parallel_checkout() just writes the queued entries in sequence (without spawning additional workers). The next patch will actually implement the parallelism and, later, we will make it configurable. Note that, to avoid potential data races, not all entries are eligible for parallel checkout. Also, paths that collide on disk (e.g. case-sensitive paths in case-insensitive file systems), are detected by the parallel checkout code and skipped, so that they can be safely sequentially handled later. The collision detection works like the following: - If the collision was at basename (e.g. 'a/b' and 'a/B'), the framework detects it by looking for EEXIST and EISDIR errors after an open(O_CREAT | O_EXCL) failure. - If the collision was at dirname (e.g. 'a/b' and 'A'), it is detected at the has_dirs_only_path() check, which is done for the leading path of each item in the parallel checkout queue. Both verifications rely on the fact that, before enqueueing an entry for parallel checkout, checkout_entry() makes sure that there is no file at the entry's path and that its leading components are all real directories. So, any later change in these conditions indicates that there was a collision (either between two parallel-eligible entries or between an eligible and an ineligible one). After all parallel-eligible entries have been processed, the collided (and thus, skipped) entries are sequentially fed to checkout_entry() again. This is similar to the way the current code deals with collisions, overwriting the previously checked out entries with the subsequent ones. The only difference is that, since we no longer create the files in the same order that they appear on index, we are not able to determine which of the colliding entries will survive on disk (for the classic code, it is always the last entry). Co-authored-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Co-authored-by: Jeff Hostetler <jeffhost@microsoft.com> Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br> Signed-off-by: Junio C Hamano <gitster@pobox.com>
33 lines
816 B
C
33 lines
816 B
C
#ifndef PARALLEL_CHECKOUT_H
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#define PARALLEL_CHECKOUT_H
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struct cache_entry;
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struct checkout;
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struct conv_attrs;
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enum pc_status {
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PC_UNINITIALIZED = 0,
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PC_ACCEPTING_ENTRIES,
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PC_RUNNING,
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};
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enum pc_status parallel_checkout_status(void);
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/*
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* Put parallel checkout into the PC_ACCEPTING_ENTRIES state. Should be used
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* only when in the PC_UNINITIALIZED state.
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*/
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void init_parallel_checkout(void);
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/*
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* Return -1 if parallel checkout is currently not accepting entries or if the
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* entry is not eligible for parallel checkout. Otherwise, enqueue the entry
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* for later write and return 0.
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*/
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int enqueue_checkout(struct cache_entry *ce, struct conv_attrs *ca);
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/* Write all the queued entries, returning 0 on success.*/
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int run_parallel_checkout(struct checkout *state);
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#endif /* PARALLEL_CHECKOUT_H */
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