thodg/libgit2

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  • Hash : a7c60cfc
    Author : Shawn O. Pearce
    Date : 2009-01-03T02:41:26

    Add basic support to read pack-*.idx v1 and v2 files The index data is mapped into memory and then scanned using a binary search algorithm to locate the matching entry for the supplied git_oid. The standard fanout hash trick is applied to reduce the search space by 8 iterations. Since the v1 and v2 file formats differ in their search function, due to the different layouts used for the object records, we use two different search implementations and a virtual function pointer to jump to the correct version of code for the current pack index. The single function jump per-pack should be faster then computing a branch point inside the inner loop of a common binary search. To improve concurrency during read operations the pack lock is only held while verifying the index is actually open, or while opening the index for the first time. This permits multiple concurrent readers to scan through the same index. If an invalid index file is opened we close it and mark the git_pack's invalid bit to true. The git_pack structure is kept around in its parent git_packlist, but the invalid bit will cause all future readers to skip over the pack entirely. Pruning the invalid entries is relatively unimportant because they shouldn't be very common, a $GIT_DIRECTORY/objects/pack directory tends to only have valid pack files. Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

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