json: Add conditionals to avoid locking if Jansson is thread safe.

Jansson is thread safe for all read-only functions and reference
counting starting v2.11.  This allows simplification of our code and
removal of locking around reference counting and dumping.

Change-Id: Id985cb3ffa6681f9ac765642e20fcd187bd4aeee

contrib/scripts/install_prereq

@@ -56,7 +56,7 @@ PACKAGES_FBSD="$PACKAGES_FBSD sqlite3 libxslt jansson e2fsprogs-libuuid gsm libs
 
 KVERS=`uname -r`
 
-JANSSON_VER=2.10
+JANSSON_VER=2.11
 
 case "$1" in
 test)

main/json.c

@@ -44,6 +44,21 @@
 #include <jansson.h>
 #include <time.h>
 
+#if defined(JANSSON_THREAD_SAFE_REFCOUNT)
+void *ast_json_malloc(size_t size)
+{
+	return ast_malloc(size);
+}
+
+void ast_json_free(void *p)
+{
+	ast_free(p);
+}
+
+/* No need to lock since jansson is thread safe. */
+#define SCOPED_JSON_LOCK(json)
+
+#else
 /*! \brief Magic number, for safety checks. */
 #define JSON_MAGIC 0x1541992
 
@@ -187,6 +202,7 @@ void ast_json_free(void *p)
 
 	AST_LIST_INSERT_HEAD(free_list, mem, list);
 }
+#endif
 
 void ast_json_set_alloc_funcs(void *(*malloc_fn)(size_t), void (*free_fn)(void*))
 {
@@ -200,7 +216,7 @@ void ast_json_reset_alloc_funcs(void)
 
 struct ast_json *ast_json_ref(struct ast_json *json)
 {
-	/* Jansson refcounting is non-atomic; lock it. */
+	/* If Jansson refcounting is non-atomic; lock it. */
 	SCOPED_JSON_LOCK(json);
 	json_incref((json_t *)json);
 	return json;
@@ -208,6 +224,9 @@ struct ast_json *ast_json_ref(struct ast_json *json)
 
 void ast_json_unref(struct ast_json *json)
 {
+#if defined(JANSSON_THREAD_SAFE_REFCOUNT)
+	json_decref((json_t *) json);
+#else
 	struct json_mem_list *free_list;
 	struct json_mem *mem;
 
@@ -232,6 +251,7 @@ void ast_json_unref(struct ast_json *json)
 	while ((mem = AST_LIST_REMOVE_HEAD(free_list, list))) {
 		json_mem_free(mem);
 	}
+#endif
 }
 
 enum ast_json_type ast_json_typeof(const struct ast_json *json)
@@ -664,7 +684,11 @@ char *ast_json_dump_string_format(struct ast_json *root, enum ast_json_encoding_
 {
 	/* 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. */
+	 * See http://www.digip.org/jansson/doc/2.4/portability.html#thread-safety.
+	 *
+	 * This comment does not apply when JANSSON_THREAD_SAFE_REFCOUNT is defined,
+	 * in that case SCOPED_JSON_LOCK is a no-op.
+	 */
 	SCOPED_JSON_LOCK(root);
 	return json_dumps((json_t *)root, dump_flags(format));
 }
@@ -704,7 +728,11 @@ int ast_json_dump_str_format(struct ast_json *root, struct ast_str **dst, enum a
 {
 	/* 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. */
+	 * See http://www.digip.org/jansson/doc/2.4/portability.html#thread-safety.
+	 *
+	 * This comment does not apply when JANSSON_THREAD_SAFE_REFCOUNT is defined,
+	 * in that case SCOPED_JSON_LOCK is a no-op.
+	 */
 	SCOPED_JSON_LOCK(root);
 	return json_dump_callback((json_t *)root, write_to_ast_str, dst, dump_flags(format));
 }
@@ -714,7 +742,11 @@ int ast_json_dump_file_format(struct ast_json *root, FILE *output, enum ast_json
 {
 	/* 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. */
+	 * See http://www.digip.org/jansson/doc/2.4/portability.html#thread-safety.
+	 *
+	 * This comment does not apply when JANSSON_THREAD_SAFE_REFCOUNT is defined,
+	 * in that case SCOPED_JSON_LOCK is a no-op.
+	 */
 	SCOPED_JSON_LOCK(root);
 	if (!root || !output) {
 		return -1;
@@ -725,7 +757,11 @@ int ast_json_dump_new_file_format(struct ast_json *root, const char *path, enum
 {
 	/* 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. */
+	 * See http://www.digip.org/jansson/doc/2.4/portability.html#thread-safety.
+	 *
+	 * This comment does not apply when JANSSON_THREAD_SAFE_REFCOUNT is defined,
+	 * in that case SCOPED_JSON_LOCK is a no-op.
+	 */
 	SCOPED_JSON_LOCK(root);
 	if (!root || !path) {
 		return -1;