diff options
| author | Jeff Hostetler <jeffhost@microsoft.com> | 2017-09-06 18:43:48 +0300 |
|---|---|---|
| committer | Junio C Hamano <gitster@pobox.com> | 2017-09-07 03:42:02 +0300 |
| commit | 8b604d19515c4be18403047045faa363d4de217b (patch) | |
| tree | 5bb6fb5e265c3f46c0a08b498c6ee2159dc326cc /name-hash.c | |
| parent | 238e487ea943f80734cc6dad665e7238b8cbc7ff (diff) | |
hashmap: add API to disable item counting when threaded
This is to address concerns raised by ThreadSanitizer on the mailing list
about threaded unprotected R/W access to map.size with my previous "disallow
rehash" change (0607e10009ee4e37cb49b4cec8d28a9dda1656a4).
See:
https://public-inbox.org/git/adb37b70139fd1e2bac18bfd22c8b96683ae18eb.1502780344.git.martin.agren@gmail.com/
Add API to hashmap to disable item counting and thus automatic rehashing.
Also include API to later re-enable them.
When item counting is disabled, the map.size field is invalid. So to
prevent accidents, the field has been renamed and an accessor function
hashmap_get_size() has been added. All direct references to this
field have been been updated. And the name of the field changed
to map.private_size to communicate this.
Here is the relevant output from ThreadSanitizer showing the problem:
WARNING: ThreadSanitizer: data race (pid=10554)
Read of size 4 at 0x00000082d488 by thread T2 (mutexes: write M16):
#0 hashmap_add hashmap.c:209
#1 hash_dir_entry_with_parent_and_prefix name-hash.c:302
#2 handle_range_dir name-hash.c:347
#3 handle_range_1 name-hash.c:415
#4 lazy_dir_thread_proc name-hash.c:471
#5 <null> <null>
Previous write of size 4 at 0x00000082d488 by thread T1 (mutexes: write M31):
#0 hashmap_add hashmap.c:209
#1 hash_dir_entry_with_parent_and_prefix name-hash.c:302
#2 handle_range_dir name-hash.c:347
#3 handle_range_1 name-hash.c:415
#4 handle_range_dir name-hash.c:380
#5 handle_range_1 name-hash.c:415
#6 lazy_dir_thread_proc name-hash.c:471
#7 <null> <null>
Martin gives instructions for running TSan on test t3008 in this post:
https://public-inbox.org/git/CAN0heSoJDL9pWELD6ciLTmWf-a=oyxe4EXXOmCKvsG5MSuzxsA@mail.gmail.com/
Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'name-hash.c')
| -rw-r--r-- | name-hash.c | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/name-hash.c b/name-hash.c index bd8dc7a6a7..45c98db0a0 100644 --- a/name-hash.c +++ b/name-hash.c @@ -584,9 +584,15 @@ static void lazy_init_name_hash(struct index_state *istate) hashmap_init(&istate->dir_hash, dir_entry_cmp, NULL, istate->cache_nr); if (lookup_lazy_params(istate)) { - hashmap_disallow_rehash(&istate->dir_hash, 1); + /* + * Disable item counting and automatic rehashing because + * we do per-chain (mod n) locking rather than whole hashmap + * locking and we need to prevent the table-size from changing + * and bucket items from being redistributed. + */ + hashmap_disable_item_counting(&istate->dir_hash); threaded_lazy_init_name_hash(istate); - hashmap_disallow_rehash(&istate->dir_hash, 0); + hashmap_enable_item_counting(&istate->dir_hash); } else { int nr; for (nr = 0; nr < istate->cache_nr; nr++) |