It is obviously quite a serious problem if this happens, but mutex
initialization can fail and we should detect it. It's a bit like
a memory allocation failure, in that you're probably pretty screwed
if this occurs, but at least we'll catch it.
By zeroing out the memory when we free larger objects (i.e. those
that serve as collections of other data, such as repos, odb, refdb),
I'm hoping that it will be easier for libgit2 bindings to find
errors in their object management code.
This adds docs for the cache control options to git_libgit2_opts
and also tweaks the cache code so that if the cache is disabled,
then the next time we attempt to insert something into the cache
in question, we will actually clear any old cached objects.
This adds create and free callback to the git_objects_table so
that more of the creation and destruction of objects can be table
driven instead of using switch statements. This also makes the
semantics of certain object creation functions consistent so that
we can make better use of function pointers. This also fixes a
theoretical error case where an object allocation fails and we
end up storing NULL into the cache.
Add a git_cache_set_max_object_size method that does more checking
around setting the max object size. Also add a git_cache_size to
read the number of objects currently in the cache. This makes it
easier to write tests.
Example: a cached node is owned only by the cache (refcount == 1).
Thread A holds the lock and determines that the entry which should get
cached equals the node (git_oid_cmp(&node->oid, &entry->oid) == 0).
It frees the given entry to instead return the cached node to the user
(entry = node). Now, before Thread A happens to increment the refcount
of the node *outside* the cache lock, Thread B tries to store another
entry and hits the slot of the node before, decrements its refcount and
frees it *before* Thread A gets a chance to increment for the user.
git_cached_obj_incref(entry);
git_mutex_lock(&cache->lock);
{
git_cached_obj *node = cache->nodes[hash & cache->size_mask];
if (node == NULL) {
cache->nodes[hash & cache->size_mask] = entry;
} else if (git_oid_cmp(&node->oid, &entry->oid) == 0) {
git_cached_obj_decref(entry, cache->free_obj);
entry = node;
} else {
git_cached_obj_decref(node, cache->free_obj);
// Thread B is here
cache->nodes[hash & cache->size_mask] = entry;
}
}
git_mutex_unlock(&cache->lock);
// Thread A is here
/* increase the refcount again, because we are
* returning it to the user */
git_cached_obj_incref(entry);
1. The license header is technically not valid if it doesn't have a
copyright signature.
2. The COPYING file has been updated with the different licenses used in
the project.
3. The full GPLv2 header in each file annoys me.
Now we use a simple closed-addressing cache. Cuckoo hashing was creating
too many issues with race conditions. Fuck that.
Let's see what happens performance wise, we may have to roll back or
come up with another way to implement an efficient multi-threaded cache.
Hey. Apologies in advance -- I broke your bindings.
This is a major commit that includes a long-overdue redesign of the
whole object-database structure. This is expected to be the last major
external API redesign of the library until the first non-alpha release.
Please get your bindings up to date with these changes. They will be
included in the next minor release. Sorry again!
Major features include:
- Real caching and refcounting on parsed objects
- Real caching and refcounting on objects read from the ODB
- Streaming writes & reads from the ODB
- Single-method writes for all object types
- The external API is now partially thread-safe
The speed increases are significant in all aspects, specially when
reading an object several times from the ODB (revwalking) and when
writing big objects to the ODB.
Here's a full changelog for the external API:
blob.h
------
- Remove `git_blob_new`
- Remove `git_blob_set_rawcontent`
- Remove `git_blob_set_rawcontent_fromfile`
- Rename `git_blob_writefile` -> `git_blob_create_fromfile`
- Change `git_blob_create_fromfile`:
The `path` argument is now relative to the repository's working dir
- Add `git_blob_create_frombuffer`
commit.h
--------
- Remove `git_commit_new`
- Remove `git_commit_add_parent`
- Remove `git_commit_set_message`
- Remove `git_commit_set_committer`
- Remove `git_commit_set_author`
- Remove `git_commit_set_tree`
- Add `git_commit_create`
- Add `git_commit_create_v`
- Add `git_commit_create_o`
- Add `git_commit_create_ov`
tag.h
-----
- Remove `git_tag_new`
- Remove `git_tag_set_target`
- Remove `git_tag_set_name`
- Remove `git_tag_set_tagger`
- Remove `git_tag_set_message`
- Add `git_tag_create`
- Add `git_tag_create_o`
tree.h
------
- Change `git_tree_entry_2object`:
New signature is `(git_object **object_out, git_repository *repo, git_tree_entry *entry)`
- Remove `git_tree_new`
- Remove `git_tree_add_entry`
- Remove `git_tree_remove_entry_byindex`
- Remove `git_tree_remove_entry_byname`
- Remove `git_tree_clearentries`
- Remove `git_tree_entry_set_id`
- Remove `git_tree_entry_set_name`
- Remove `git_tree_entry_set_attributes`
object.h
------------
- Remove `git_object_new
- Remove `git_object_write`
- Change `git_object_close`:
This method is now *mandatory*. Not closing an object causes a
memory leak.
odb.h
-----
- Remove type `git_rawobj`
- Remove `git_rawobj_close`
- Rename `git_rawobj_hash` -> `git_odb_hash`
- Change `git_odb_hash`:
New signature is `(git_oid *id, const void *data, size_t len, git_otype type)`
- Add type `git_odb_object`
- Add `git_odb_object_close`
- Change `git_odb_read`:
New signature is `(git_odb_object **out, git_odb *db, const git_oid *id)`
- Change `git_odb_read_header`:
New signature is `(size_t *len_p, git_otype *type_p, git_odb *db, const git_oid *id)`
- Remove `git_odb_write`
- Add `git_odb_open_wstream`
- Add `git_odb_open_rstream`
odb_backend.h
-------------
- Change type `git_odb_backend`:
New internal signatures are as follows
int (* read)(void **, size_t *, git_otype *, struct git_odb_backend *, const git_oid *)
int (* read_header)(size_t *, git_otype *, struct git_odb_backend *, const git_oid *)
int (* writestream)(struct git_odb_stream **, struct git_odb_backend *, size_t, git_otype)
int (* readstream)( struct git_odb_stream **, struct git_odb_backend *, const git_oid *)
- Add type `git_odb_stream`
- Add enum `git_odb_streammode`
Signed-off-by: Vicent Marti <tanoku@gmail.com>
