Add mutex around mapping and unmapping pack files

When I was writing threading tests for the new cache, the main
error I kept running into was a pack file having it's content
unmapped underneath the running thread.  This adds a lock around
the routines that map and unmap the pack data so that threads can
effectively reload the data when they need it.

This also required reworking the error handling paths in a couple
places in the code which I tried to make consistent.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/pack.h b/src/pack.h
index 8d7e33dfe..b734ac163 100644
--- a/src/pack.h
+++ b/src/pack.h
@@ -79,6 +79,7 @@ typedef struct {
 struct git_pack_file {
 	git_mwindow_file mwf;
 	git_map index_map;
+	git_mutex lock;
 
 	uint32_t num_objects;
 	uint32_t num_bad_objects;