[PATCH] read-cache: call verify_hdr() in a background thread

From: Jeff Hostetler <jeffhost@microsoft.com>

This patch contains a performance optimization to run verify_hdr() in a background thread while the foreground thread parses the index. This allows do_read_index() to complete faster.

This idea was recently discussed on the mailing list in: https://public-inbox.org/git/85221b97-759f-b7a9-1256-21515d163cbf@jeffhostetler.com/ during a discussion on sha1dc.

Our testing on Windows showed that verifying the SHA1 hash on the index file takes approximately the same amount of time as parsing the file and building the array of cache_entries. (It could also be that having 2 threads better ammortizes the page faults of reading from the mmap'd file.)

An earlier version of this change has been in use in GfW since December: https://github.com/git-for-windows/git/pull/978

Jeff Hostetler (1):
  read-cache: call verify_hdr() in a background thread

 read-cache.c | 87 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 86 insertions(+), 1 deletion(-)