diff options
Diffstat (limited to 'libobjc/sendmsg.c')
| -rw-r--r-- | libobjc/sendmsg.c | 72 |
1 files changed, 58 insertions, 14 deletions
diff --git a/libobjc/sendmsg.c b/libobjc/sendmsg.c index 71e89667134..0214e77afcd 100644 --- a/libobjc/sendmsg.c +++ b/libobjc/sendmsg.c @@ -119,6 +119,14 @@ __inline__ IMP get_imp (Class class, SEL sel) { + /* In a vanilla implementation we would first check if the dispatch + table is installed. Here instead, to get more speed in the + standard case (that the dispatch table is installed) we first try + to get the imp using brute force. Only if that fails, we do what + we should have been doing from the very beginning, that is, check + if the dispatch table needs to be installed, install it if it's + not installed, and retrieve the imp from the table if it's + installed. */ void *res = sarray_get_safe (class->dtable, (size_t) sel->sel_id); if (res == 0) { @@ -127,7 +135,16 @@ get_imp (Class class, SEL sel) { /* The dispatch table needs to be installed. */ objc_mutex_lock (__objc_runtime_mutex); - __objc_install_dispatch_table_for_class (class); + + /* Double-checked locking pattern: Check + __objc_uninstalled_dtable again in case another thread + installed the dtable while we were waiting for the lock + to be released. */ + if (class->dtable == __objc_uninstalled_dtable) + { + __objc_install_dispatch_table_for_class (class); + } + objc_mutex_unlock (__objc_runtime_mutex); /* Call ourselves with the installed dispatch table and get the real method */ @@ -135,10 +152,22 @@ get_imp (Class class, SEL sel) } else { - /* The dispatch table has been installed so the - method just doesn't exist for the class. - Return the forwarding implementation. */ - res = __objc_get_forward_imp (sel); + /* The dispatch table has been installed. */ + + /* Get the method from the dispatch table (we try to get it + again in case another thread has installed the dtable just + after we invoked sarray_get_safe, but before we checked + class->dtable == __objc_uninstalled_dtable). + */ + res = sarray_get_safe (class->dtable, (size_t) sel->sel_id); + if (res == 0) + { + /* The dispatch table has been installed, and the method + is not in the dispatch table. So the method just + doesn't exist for the class. Return the forwarding + implementation. */ + res = __objc_get_forward_imp (sel); + } } } return res; @@ -157,7 +186,10 @@ __objc_responds_to (id object, SEL sel) if (object->class_pointer->dtable == __objc_uninstalled_dtable) { objc_mutex_lock (__objc_runtime_mutex); - __objc_install_dispatch_table_for_class (object->class_pointer); + if (object->class_pointer->dtable == __objc_uninstalled_dtable) + { + __objc_install_dispatch_table_for_class (object->class_pointer); + } objc_mutex_unlock (__objc_runtime_mutex); } @@ -192,10 +224,19 @@ objc_msg_lookup (id receiver, SEL op) } else { - /* The dispatch table has been installed so the - method just doesn't exist for the class. - Attempt to forward the method. */ - result = __objc_get_forward_imp (op); + /* The dispatch table has been installed. Check again + if the method exists (just in case the dispatch table + has been installed by another thread after we did the + previous check that the method exists). + */ + result = sarray_get_safe (receiver->class_pointer->dtable, + (sidx)op->sel_id); + if (result == 0) + { + /* If the method still just doesn't exist for the + class, attempt to forward the method. */ + result = __objc_get_forward_imp (op); + } } } return result; @@ -239,13 +280,16 @@ __objc_init_dispatch_tables () static void __objc_init_install_dtable (id receiver, SEL op __attribute__ ((__unused__))) { + objc_mutex_lock (__objc_runtime_mutex); + /* This may happen, if the programmer has taken the address of a method before the dtable was initialized... too bad for him! */ if (receiver->class_pointer->dtable != __objc_uninstalled_dtable) - return; - - objc_mutex_lock (__objc_runtime_mutex); - + { + objc_mutex_unlock (__objc_runtime_mutex); + return; + } + if (CLS_ISCLASS (receiver->class_pointer)) { /* receiver is an ordinary object */ |