Author: dlee Date: Fri Aug 2 09:27:35 2013 New Revision: 396119 URL: http://svnview.digium.com/svn/asterisk?view=rev&rev=396119 Log: Address JSON thread safety issues.
In tracking down some unit tests failures, I ended up reading the fine print[1] regarding Jansson's thread safety. In short: 1. Ref-counting is non-atomic. 2. json_dumps() and friends are not thread safe. This patch adds locking where necessary to our ast_json_* wrapper API, with documentation in json.h describing the thread safety limitations of the API. [1]: http://www.digip.org/jansson/doc/2.4/portability.html#thread-safety Modified: trunk/include/asterisk/json.h trunk/main/cel.c trunk/main/json.c trunk/res/ari/ari_websockets.c trunk/res/res_sorcery_astdb.c trunk/tests/test_json.c Modified: trunk/include/asterisk/json.h URL: http://svnview.digium.com/svn/asterisk/trunk/include/asterisk/json.h?view=diff&rev=396119&r1=396118&r2=396119 ============================================================================== --- trunk/include/asterisk/json.h (original) +++ trunk/include/asterisk/json.h Fri Aug 2 09:27:35 2013 @@ -42,6 +42,37 @@ * In the cases where you have a need to introduce intermediate objects, just * wrap them with json_ref() when passing them to other \c ast_json_*() * functions. + * + * \par Thread Safety + * + * Jansson (as of 2.4) provides fairly weak thread safety guarantees. The + * Asterisk wrapper improves upon that slightly. The remaining refcounting + * problems are issues when slicing/sharing/mixing instances between JSON + * objects and arrays, which we avoid. + * + * The \c ast_json_dump_* functions are thread safe for multiple concurrent + * dumps of the same object, so long as the concurrent dumps start from the same + * \c root object. But if an object is shared by other JSON objects/arrays, then + * concurrent dumps of the outer objects/arrays are not thread safe. This can be + * avoided by using ast_json_deep_copy() when sharing JSON instances between + * objects. + * + * The ast_json_ref() and ast_json_unref() functions are thread safe. Since the + * Asterisk wrapper exclusively uses the reference stealing API, Jansson won't + * be performing many refcount modifications behind our backs. There are a few + * exceptions. + * + * The first is the transitive json_decref() that occurs when \ref + * AST_JSON_OBJECT and \ref AST_JSON_ARRAY instances are deleted. This can be + * avoided by using ast_json_deep_copy() when sharing JSON instances between + * objects. + * + * The second is when using the reference borrowing specifier in + * ast_json_pack() (capital \c O). This can be avoided by using the reference + * stealing specifier (lowercase \c o) and wrapping the JSON object parameter + * with ast_json_ref() for an explicit ref-bump. + * + * \par Example code * * \code * // Example of how to use the Asterisk JSON API @@ -105,6 +136,20 @@ * ast_free(). */ void ast_json_reset_alloc_funcs(void); + +/*! + * \brief Asterisk's custom JSON allocator. Exposed for use by unit tests. + * \since 12.0.0 + * \internal + */ +void *ast_json_malloc(size_t size); + +/*! + * \brief Asterisk's custom JSON allocator. Exposed for use by unit tests. + * \since 12.0.0 + * \internal + */ +void ast_json_free(void *p); /*! * \struct ast_json @@ -683,13 +728,23 @@ AST_JSON_PRETTY, }; +/*! + * \brief Encode a JSON value to a compact string. + * \since 12.0.0 + * + * Returned string must be freed by calling ast_json_free(). + * + * \param root JSON value. + * \return String encoding of \a root. + * \return \c NULL on error. + */ #define ast_json_dump_string(root) ast_json_dump_string_format(root, AST_JSON_COMPACT) /*! * \brief Encode a JSON value to a string. * \since 12.0.0 * - * Returned string must be freed by calling ast_free(). + * Returned string must be freed by calling ast_json_free(). * * \param root JSON value. * \param format encoding format type. Modified: trunk/main/cel.c URL: http://svnview.digium.com/svn/asterisk/trunk/main/cel.c?view=diff&rev=396119&r1=396118&r2=396119 ============================================================================== --- trunk/main/cel.c (original) +++ trunk/main/cel.c Fri Aug 2 09:27:35 2013 @@ -638,7 +638,7 @@ struct ast_json *extra, const char *peer_name) { struct timeval eventtime = ast_tvnow(); - RAII_VAR(char *, extra_txt, NULL, ast_free); + RAII_VAR(char *, extra_txt, NULL, ast_json_free); if (extra) { extra_txt = ast_json_dump_string(extra); } Modified: trunk/main/json.c URL: http://svnview.digium.com/svn/asterisk/trunk/main/json.c?view=diff&rev=396119&r1=396118&r2=396119 ============================================================================== --- trunk/main/json.c (original) +++ trunk/main/json.c Fri Aug 2 09:27:35 2013 @@ -20,8 +20,8 @@ * * \brief JSON abstraction layer. * - * This is a very thin wrapper around the Jansson API. For more details on it, see its - * docs at http://www.digip.org/jansson/doc/2.4/apiref.html. + * This is a very thin wrapper around the Jansson API. For more details on it, + * see its docs at http://www.digip.org/jansson/doc/2.4/apiref.html. * * \author David M. Lee, II <[email protected]> */ @@ -46,20 +46,148 @@ #include <jansson.h> #include <time.h> +/*! \brief Magic number, for safety checks. */ +#define JSON_MAGIC 0x1541992 + +/*! \brief Internal structure for allocated memory blocks */ +struct json_mem { + /*! Magic number, for safety checks */ + uint32_t magic; + /*! Mutext for locking this memory block */ + ast_mutex_t mutex; + /*! Linked list pointer for the free list */ + AST_LIST_ENTRY(json_mem) list; + /*! Data section of the allocation; void pointer for proper alignment */ + void *data[]; +}; + +/*! \brief Free a \ref json_mem block. */ +static void json_mem_free(struct json_mem *mem) +{ + mem->magic = 0; + ast_mutex_destroy(&mem->mutex); + ast_free(mem); +} + /*! - * \brief Function wrapper around ast_malloc macro. - */ -static void *json_malloc(size_t size) -{ - return ast_malloc(size); + * \brief Get the \ref json_mem block for a pointer allocated via + * ast_json_malloc(). + * + * This function properly handles Jansson singletons (null, true, false), and + * \c NULL. + * + * \param p Pointer, usually to a \c json_t or \ref ast_json. + * \return \ref json_mem object with extra allocation info. + */ +static inline struct json_mem *to_json_mem(void *p) +{ + struct json_mem *mem; + /* Avoid ref'ing the singleton values */ + if (p == NULL || p == json_null() || p == json_true() || + p == json_false()) { + return NULL; + } + mem = (struct json_mem *)((char *) (p) - sizeof(*mem)); + ast_assert(mem->magic == JSON_MAGIC); + return mem; } /*! - * \brief Function wrapper around ast_free macro. - */ -static void json_free(void *p) -{ - ast_free(p); + * \brief Lock an \ref ast_json instance. + * + * If \a json is an immutable singleton (null, true, false), this function + * safely ignores it and returns \c NULL. Otherwise, \a json must have been + * allocates using ast_json_malloc(). + * + * \param json JSON instance to lock. + * \return \ref Corresponding \ref json_mem block. + * \return \c NULL if \a json was not allocated. + */ +static struct json_mem *json_mem_lock(struct ast_json *json) +{ + struct json_mem *mem = to_json_mem(json); + if (!mem) { + return NULL; + } + ast_mutex_lock(&mem->mutex); + return mem; +} + +/*! + * \brief Unlock a \ref json_mem instance. + * + * \param mem \ref json_mem, usually returned from json_mem_lock(). + */ +static void json_mem_unlock(struct json_mem *mem) +{ + if (!mem) { + return; + } + ast_mutex_unlock(&mem->mutex); +} + +/*! + * \brief Scoped lock for a \ref ast_json instance. + * + * \param json JSON instance to lock. + */ +#define SCOPED_JSON_LOCK(json) \ + RAII_VAR(struct json_mem *, __mem_ ## __LINE__, \ + json_mem_lock(json), json_mem_unlock) + +void *ast_json_malloc(size_t size) +{ + struct json_mem *mem = ast_malloc(size + sizeof(*mem)); + if (!mem) { + return NULL; + } + mem->magic = JSON_MAGIC; + ast_mutex_init(&mem->mutex); + return mem->data; +} + +AST_THREADSTORAGE(json_free_list_ts); + +/*! + * \brief Struct for a linked list of \ref json_mem. + */ +AST_LIST_HEAD_NOLOCK(json_mem_list, json_mem); + +/*! + * \brief Thread local list of \ref json_mem blocks to free at the end of an + * unref. + */ +static struct json_mem_list *json_free_list(void) +{ + return ast_threadstorage_get(&json_free_list_ts, + sizeof(struct json_mem_list)); +} + +void ast_json_free(void *p) +{ + struct json_mem *mem; + struct json_mem_list *free_list; + mem = to_json_mem(p); + + if (!mem) { + return; + } + + /* Since the unref is holding a lock in mem, we can't free it + * immediately. Store it off on a thread local list to be freed by + * ast_json_unref(). + */ + free_list = json_free_list(); + if (!free_list) { + ast_log(LOG_ERROR, "Error allocating free list\n"); + ast_assert(0); + /* It's not ideal to free the memory immediately, but that's the + * best we can do if the threadlocal allocation fails */ + json_mem_free(mem); + return; + } + + AST_LIST_INSERT_HEAD(free_list, mem, list); } void ast_json_set_alloc_funcs(void *(*malloc_fn)(size_t), void (*free_fn)(void*)) @@ -69,21 +197,41 @@ void ast_json_reset_alloc_funcs(void) { - json_set_alloc_funcs(json_malloc, json_free); + json_set_alloc_funcs(ast_json_malloc, ast_json_free); } struct ast_json *ast_json_ref(struct ast_json *json) { + /* Jansson refcounting is non-atomic; lock it. */ + SCOPED_JSON_LOCK(json); json_incref((json_t *)json); return json; } void ast_json_unref(struct ast_json *json) { - if (!json) { + struct json_mem_list *free_list; + struct json_mem *mem; + + /* Jansson refcounting is non-atomic; lock it. */ + { + SCOPED_JSON_LOCK(json); + if (!json) { + return; + } + json_decref((json_t *)json); + } + + /* Now free any objects that were ast_json_free()'s while the lock was + * held */ + free_list = json_free_list(); + if (!free_list) { return; } - json_decref((json_t *)json); + + while ((mem = AST_LIST_REMOVE_HEAD(free_list, list))) { + json_mem_free(mem); + } } enum ast_json_type ast_json_typeof(const struct ast_json *json) @@ -383,6 +531,10 @@ char *ast_json_dump_string_format(struct ast_json *root, enum ast_json_encoding_format format) { + /* Jansson's json_dump*, even though it's a read operation, isn't + * thread safe for concurrent reads. Locking is necessary. + * See http://www.digip.org/jansson/doc/2.4/portability.html#thread-safety. */ + SCOPED_JSON_LOCK(root); return json_dumps((json_t *)root, dump_flags(format)); } @@ -419,12 +571,20 @@ int ast_json_dump_str_format(struct ast_json *root, struct ast_str **dst, enum ast_json_encoding_format format) { + /* Jansson's json_dump*, even though it's a read operation, isn't + * thread safe for concurrent reads. Locking is necessary. + * See http://www.digip.org/jansson/doc/2.4/portability.html#thread-safety. */ + SCOPED_JSON_LOCK(root); return json_dump_callback((json_t *)root, write_to_ast_str, dst, dump_flags(format)); } int ast_json_dump_file_format(struct ast_json *root, FILE *output, enum ast_json_encoding_format format) { + /* Jansson's json_dump*, even though it's a read operation, isn't + * thread safe for concurrent reads. Locking is necessary. + * See http://www.digip.org/jansson/doc/2.4/portability.html#thread-safety. */ + SCOPED_JSON_LOCK(root); if (!root || !output) { return -1; } @@ -432,6 +592,10 @@ } int ast_json_dump_new_file_format(struct ast_json *root, const char *path, enum ast_json_encoding_format format) { + /* Jansson's json_dump*, even though it's a read operation, isn't + * thread safe for concurrent reads. Locking is necessary. + * See http://www.digip.org/jansson/doc/2.4/portability.html#thread-safety. */ + SCOPED_JSON_LOCK(root); if (!root || !path) { return -1; } Modified: trunk/res/ari/ari_websockets.c URL: http://svnview.digium.com/svn/asterisk/trunk/res/ari/ari_websockets.c?view=diff&rev=396119&r1=396118&r2=396119 ============================================================================== --- trunk/res/ari/ari_websockets.c (original) +++ trunk/res/ari/ari_websockets.c Fri Aug 2 09:27:35 2013 @@ -142,7 +142,7 @@ int ast_ari_websocket_session_write(struct ast_ari_websocket_session *session, struct ast_json *message) { - RAII_VAR(char *, str, NULL, ast_free); + RAII_VAR(char *, str, NULL, ast_json_free); #ifdef AST_DEVMODE if (!session->validator(message)) { Modified: trunk/res/res_sorcery_astdb.c URL: http://svnview.digium.com/svn/asterisk/trunk/res/res_sorcery_astdb.c?view=diff&rev=396119&r1=396118&r2=396119 ============================================================================== --- trunk/res/res_sorcery_astdb.c (original) +++ trunk/res/res_sorcery_astdb.c Fri Aug 2 09:27:35 2013 @@ -126,7 +126,7 @@ static int sorcery_astdb_create(const struct ast_sorcery *sorcery, void *data, void *object) { RAII_VAR(struct ast_json *, objset, ast_sorcery_objectset_json_create(sorcery, object), ast_json_unref); - RAII_VAR(char *, value, NULL, ast_free_ptr); + RAII_VAR(char *, value, NULL, ast_json_free); const char *prefix = data; char family[strlen(prefix) + strlen(ast_sorcery_object_get_type(object)) + 2]; Modified: trunk/tests/test_json.c URL: http://svnview.digium.com/svn/asterisk/trunk/tests/test_json.c?view=diff&rev=396119&r1=396118&r2=396119 ============================================================================== --- trunk/tests/test_json.c (original) +++ trunk/tests/test_json.c Fri Aug 2 09:27:35 2013 @@ -55,7 +55,7 @@ */ static void *json_debug_malloc(size_t size) { - void *p = ast_malloc(size); + void *p = ast_json_malloc(size); if (p) { ++alloc_count; } @@ -67,7 +67,7 @@ if (p) { --alloc_count; } - ast_free(p); + ast_json_free(p); } static int json_test_init(struct ast_test_info *info, struct ast_test *test) -- _____________________________________________________________________ -- Bandwidth and Colocation Provided by http://www.api-digital.com -- svn-commits mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/svn-commits
