[PATCH 3/3] pack-objects (mingw): initialize `packing_data` mutex in the correct spot

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

In 9ac3f0e5b3e4 (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 even 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 the
`prepare_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 the
`packing_data` struct is used that contains that mutex.

This fixes https://github.com/git-for-windows/git/issues/1839.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 builtin/pack-objects.c        | 1 -
 pack-objects.c                | 3 +++
 t/t5321-pack-large-objects.sh | 2 +-
 3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index e6316d294d..e752cf9c7a 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -2363,7 +2363,6 @@ static void init_threaded_search(void)
 	pthread_mutex_init(&cache_mutex, NULL);
 	pthread_mutex_init(&progress_mutex, NULL);
 	pthread_cond_init(&progress_cond, NULL);
-	pthread_mutex_init(&to_pack.lock, NULL);
 	old_try_to_free_routine = set_try_to_free_routine(try_to_free_from_threads);
 }
 
diff --git a/pack-objects.c b/pack-objects.c
index 7e624c30eb..b6cdbb0166 100644
--- a/pack-objects.c
+++ b/pack-objects.c
@@ -148,6 +148,9 @@ void prepare_packing_data(struct packing_data *pdata)
 					     1U << OE_SIZE_BITS);
 	pdata->oe_delta_size_limit = git_env_ulong("GIT_TEST_OE_DELTA_SIZE",
 						   1UL << OE_DELTA_SIZE_BITS);
+#ifndef NO_PTHREADS
+	pthread_mutex_init(&pdata->lock, NULL);
+#endif
 }
 
 struct object_entry *packlist_alloc(struct packing_data *pdata,
diff --git a/t/t5321-pack-large-objects.sh b/t/t5321-pack-large-objects.sh
index c36c66fbb4..a75eab87d3 100755
--- a/t/t5321-pack-large-objects.sh
+++ b/t/t5321-pack-large-objects.sh
@@ -24,7 +24,7 @@ test_expect_success 'setup' '
 	git index-pack --stdin <ab.pack
 '
 
-test_expect_failure 'repack large deltas' '
+test_expect_success 'repack large deltas' '
 	printf "%s\\n" $A $B |
 	GIT_TEST_OE_DELTA_SIZE=2 git pack-objects tmp-pack
 '
-- 
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