Fix gc segfault

In 9ac3f0e (pack-objects: fix performance issues on packing large deltas, 2018-07-22), a mutex was introduced that is used to guard the call to set the delta size. This commit added code to initialize it, but at an incorrect
spot: in init_threaded_search(), while the call to oe_set_delta_size() (and hence to packing_data_lock()) can happen in the call chain check_object() <- get_object_details() <-prepare_pack() <- cmd_pack_objects(), which is long before theprepare_pack() function calls ll_find_deltas() (which initializes the threaded search).

Another tell-tale that the mutex was initialized in an incorrect spot is that the function to initialize it lives in builtin/, while the code that uses the mutex is defined in a libgit.a header file.

Let's use a more appropriate function: prepare_packing_data(), which not only lives in libgit.a, but has to be called before thepacking_data struct is used that contains that mutex.

Johannes Schindelin (3):
Fix typo 'detla' -> 'delta'
pack-objects (mingw): demonstrate a segmentation fault with large
deltas
pack-objects (mingw): initialize packing_data mutex in the correct
spot

 builtin/pack-objects.c        |  1 -
 pack-objects.c                |  3 +++
 pack-objects.h                |  2 +-
 t/t5321-pack-large-objects.sh | 32 ++++++++++++++++++++++++++++++++
 4 files changed, 36 insertions(+), 2 deletions(-)
 create mode 100755 t/t5321-pack-large-objects.sh

base-commit: 5a0cc8aca797dbd7d2be3b67458ff880ed45cddf
Published-As: https://github.com/gitgitgadget/git/releases/tags/pr-47%2Fjamill%2Ffix-gc-segfault-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-47/jamill/fix-gc-segfault-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/47

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