Merge pull request #2395 from libgit2/cmn/ref-iter-concurrent

Concurrent ref iterator access

src/refdb_fs.c

@@ -458,6 +458,7 @@ typedef struct {
 	git_pool pool;
 	git_vector loose;
 
+	git_sortedcache *cache;
 	size_t loose_pos;
 	size_t packed_pos;
 } refdb_fs_iter;
@@ -468,6 +469,7 @@ static void refdb_fs_backend__iterator_free(git_reference_iterator *_iter)
 
 	git_vector_free(&iter->loose);
 	git_pool_clear(&iter->pool);
+	git_sortedcache_free(iter->cache);
 	git__free(iter);
 }
 
@@ -539,10 +541,14 @@ static int refdb_fs_backend__iterator_next(
 		giterr_clear();
 	}
 
-	git_sortedcache_rlock(backend->refcache);
+	if (!iter->cache) {
+		if ((error = git_sortedcache_copy(&iter->cache, backend->refcache, 1, NULL, NULL)) < 0)
+			return error;
+	}
 
-	while (iter->packed_pos < git_sortedcache_entrycount(backend->refcache)) {
-		ref = git_sortedcache_entry(backend->refcache, iter->packed_pos++);
+	error = GIT_ITEROVER;
+	while (iter->packed_pos < git_sortedcache_entrycount(iter->cache)) {
+		ref = git_sortedcache_entry(iter->cache, iter->packed_pos++);
 		if (!ref) /* stop now if another thread deleted refs and we past end */
 			break;
 
@@ -556,7 +562,6 @@ static int refdb_fs_backend__iterator_next(
 		break;
 	}
 
-	git_sortedcache_runlock(backend->refcache);
 	return error;
 }
 
@@ -579,10 +584,14 @@ static int refdb_fs_backend__iterator_next_name(
 		giterr_clear();
 	}
 
-	git_sortedcache_rlock(backend->refcache);
+	if (!iter->cache) {
+		if ((error = git_sortedcache_copy(&iter->cache, backend->refcache, 1, NULL, NULL)) < 0)
+			return error;
+	}
 
-	while (iter->packed_pos < git_sortedcache_entrycount(backend->refcache)) {
-		ref = git_sortedcache_entry(backend->refcache, iter->packed_pos++);
+	error = GIT_ITEROVER;
+	while (iter->packed_pos < git_sortedcache_entrycount(iter->cache)) {
+		ref = git_sortedcache_entry(iter->cache, iter->packed_pos++);
 		if (!ref) /* stop now if another thread deleted refs and we past end */
 			break;
 
@@ -596,7 +605,6 @@ static int refdb_fs_backend__iterator_next_name(
 		break;
 	}
 
-	git_sortedcache_runlock(backend->refcache);
 	return error;
 }
 

tests/refs/iterator.c

@@ -186,3 +186,36 @@ void test_refs_iterator__foreach_name_can_cancel(void)
 		-333);
 	cl_assert_equal_i(0, cancel_after);
 }
+
+void test_refs_iterator__concurrent_delete(void)
+{
+	git_reference_iterator *iter;
+	size_t full_count = 0, concurrent_count = 0;
+	const char *name;
+	int error;
+
+	git_repository_free(repo);
+	repo = cl_git_sandbox_init("testrepo");
+
+	cl_git_pass(git_reference_iterator_new(&iter, repo));
+	while ((error = git_reference_next_name(&name, iter)) == 0) {
+		full_count++;
+	}
+
+	git_reference_iterator_free(iter);
+	cl_assert_equal_i(GIT_ITEROVER, error);
+
+	cl_git_pass(git_reference_iterator_new(&iter, repo));
+	while ((error = git_reference_next_name(&name, iter)) == 0) {
+		cl_git_pass(git_reference_remove(repo, name));
+		concurrent_count++;
+	}
+
+	git_reference_iterator_free(iter);
+	cl_assert_equal_i(GIT_ITEROVER, error);
+
+	cl_assert_equal_i(full_count, concurrent_count);
+
+	cl_git_sandbox_cleanup();
+	repo = NULL;
+}