On Sun, Oct 23, 2016 at 4:26 PM, Christian Couder
[off-list ref] wrote:

Doing this in read_index_from() would keep the shared file even more
"fresher" since read happens a lot more often than write. But I think
our main concern is not the temporary index files created by the user
scripts, but $GIT_DIR/index.lock (make sure we don't accidentally
delete its shared file before it gets renamed to $GIT_DIR/index). For
this case, I think refreshing in write_locked_index is enough.

                int ret = write_shared_index(istate, lock, flags);
                if (ret)
                        return ret;
+       } else {
+               /* Signal that the shared index is used */
+               const char *shared_index = git_path("sharedindex.%s",
+                                                   sha1_to_hex(si->base_sha1));
+               if (!check_and_freshen_file(shared_index, 1))
+                       warning("could not freshen '%s'", shared_index);

_()
-- 
Duy