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Improved thread-safety code by David Ayers

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git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/libobjc/trunk@32626 72102866-910b-0410-8b05-ffd578937521
main
rfm 15 years ago
parent 999c239dc3
commit ba25ea319c
2 changed files with 342 additions and 334 deletions
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5
ChangeLog
Unescape Escape View File

@ -1,3 +1,8 @@
2011-03-17 David Ayers <ayers@fsfw.org>, Richard Frith-Macdonald <rfm@gnu.org>
* sendmsg.c: Replace ugly thread-safety patch with nicer one by
David and a few further tweaks by Richard.
2011-03-05 Richard Frith-Macdonald <rfm@gnu.org>
* sendmsg.c: ugly code changes to make +initialize thread-safe.

671
sendmsg.c
Unescape Escape View File

@ -49,15 +49,6 @@ Boston, MA 02110-1301, USA. */
#define INVISIBLE_STRUCT_RETURN 0
#endif
/* Maintain a linked list of classes being initialized */
typedef struct InitializingList {
struct InitializingList *next;
Class class;
struct sarray *dtable;
} InitializingList_t;
static InitializingList_t *initializing = 0;
/* The uninstalled dispatch table */
struct sarray *__objc_uninstalled_dtable = 0; /* !T:MUTEX */
@ -74,115 +65,16 @@ IMP (*__objc_msg_forward2) (id, SEL) = NULL;
/* Send +initialize to class */
static void __objc_send_initialize (Class);
static void __objc_begin_install_dispatch_table_for_class (Class, Class);
static void __objc_end_install_dispatch_table_for_class (Class);
static void __objc_install_dispatch_table_for_class (Class, Class);
/* Forward declare some functions */
static void __objc_init_install_dtable (id, SEL);
/* Now a functio9n to check to see if a class is being initialized.
*/
static int
__objc_is_initializing_dispatch_table(Class c)
{
if (c->dtable == __objc_uninstalled_dtable)
{
InitializingList_t *list = initializing;
while (list != 0)
{
if (list->class == c)
{
return 1;
}
list = list->next;
}
}
return 0;
}
/* Set or remove the dispatch table for an initializing class in the list.
* Assumes that __objc_runtime_mutex is locked down.
*/
static void
__objc_set_initializing_dispatch_table(Class c, struct sarray *d)
{
InitializingList_t *list = initializing;
if (d == 0)
{
/* Setting 0 means removing the class */
if (list != 0)
{
if (list->class == c)
{
initializing = list->next;
objc_free (list);
return;
}
else
{
while (list->next != 0)
{
if (list->next->class == c)
{
InitializingList_t *tmp = list->next;
list->next = tmp->next;
objc_free (tmp);
return;
}
list = list->next;
}
}
}
}
else
{
while (list != 0 && list->class != c)
{
list = list->next;
}
if (list == 0)
{
list = (InitializingList_t *)objc_malloc (sizeof(InitializingList_t));
list->class = c;
list->dtable = d;
list->next = initializing;
initializing = list;
}
else
{
list->dtable = d;
}
}
}
static void __objc_install_dtable_for_class (Class cls);
static void __objc_prepare_dtable_for_class (Class cls);
static void __objc_install_prepared_dtable_for_class (Class cls);
/* Return the dispatch table of a class in the process of initialising.
* Assumes that __objc_runtime_mutex is locked down.
* If the class is not initializing, this returns the table installed
* in the class itsself.
*/
static struct sarray *
__objc_dispatch_table (Class c)
{
InitializingList_t *list = initializing;
while (list != 0)
{
if (list->class == c)
{
return list->dtable;
}
list = list->next;
}
return c->dtable;
}
static struct sarray *__objc_prepared_dtable_for_class (Class cls);
static IMP __objc_get_prepared_imp (Class cls,SEL sel);
/* Various forwarding functions that are used based upon the
return type for the selector.
o
__objc_block_forward for structures.
__objc_double_forward for floats/doubles.
__objc_word_forward for pointers or types that fit in registers. */
@ -238,7 +130,16 @@ __objc_get_forward_imp (id rcv, SEL sel)
}
}
/* Given a class and selector, return the selector's implementation. */
/* Given a CLASS and selector, return the implementation corresponding
to the method of the selector.
If CLASS is a class, the instance method is returned.
If CLASS is a meta class, the class method is returned.
Since this requires the dispatch table to be installed, this function
will implicitly invoke +initialize for CLASS if it hasn't been
invoked yet. This also insures that +initialize has been invoked
when the returned implementation is called directly. */
inline
IMP
get_imp (Class class, SEL sel)
@ -254,10 +155,8 @@ get_imp (Class class, SEL sel)
void *res = sarray_get_safe (class->dtable, (size_t) sel->sel_id);
if (res == 0)
{
struct sarray *dtable;
/* Not a valid method */
if ((dtable = class->dtable) == __objc_uninstalled_dtable)
if (class->dtable == __objc_uninstalled_dtable)
{
/* The dispatch table needs to be installed. */
objc_mutex_lock (__objc_runtime_mutex);
@ -266,60 +165,83 @@ get_imp (Class class, SEL sel)
__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_dtable_for_class (class);
/* If the dispatch table is not yet installed,
we are still in the process of executing +initialize.
But the implementation pointer should be avaliable
if it exists at all. */
if (class->dtable == __objc_uninstalled_dtable)
{
assert (__objc_prepared_dtable_for_class (class) != 0);
res = __objc_get_prepared_imp (class, sel);
}
if ((dtable = class->dtable) == __objc_uninstalled_dtable)
{
dtable = __objc_dispatch_table (class);
if (dtable == __objc_uninstalled_dtable)
{
__objc_install_dispatch_table_for_class (class, class);
dtable = __objc_dispatch_table (class);
}
}
objc_mutex_unlock (__objc_runtime_mutex);
/* Call ourselves with the installed dispatch table
and get the real method */
if (! res)
res = get_imp (class, sel);
}
/* 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 (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 ((id)class, sel);
else
{
/* 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.
We don't know the receiver (only it's class), so we
can't pass that to the function :-(
*/
res = __objc_get_forward_imp (nil, sel);
}
}
}
return res;
}
/* Query if an object can respond to a selector, returns YES if the
object implements the selector otherwise NO. Does not check if the
method can be forwarded. */
object implements the selector otherwise NO. Does not check if the
method can be forwarded.
Since this requires the dispatch table to installed, this function
will implicitly invoke +initialize for the class of OBJECT if it
hasn't been invoked yet. */
inline
BOOL
__objc_responds_to (id object, SEL sel)
{
struct sarray *dtable;
void *res;
struct sarray *dtable;
/* Install dispatch table if need be */
if ((dtable = object->class_pointer->dtable) == __objc_uninstalled_dtable)
dtable = object->class_pointer->dtable;
if (dtable == __objc_uninstalled_dtable)
{
objc_mutex_lock (__objc_runtime_mutex);
if ((dtable = object->class_pointer->dtable) == __objc_uninstalled_dtable)
if (object->class_pointer->dtable == __objc_uninstalled_dtable)
__objc_install_dtable_for_class (object->class_pointer);
/* If the dispatch table is not yet installed,
we are still in the process of executing +initialize.
Yet the dispatch table should be available. */
if (object->class_pointer->dtable == __objc_uninstalled_dtable)
{
dtable = __objc_dispatch_table (object->class_pointer);
if (dtable == __objc_uninstalled_dtable)
{
__objc_install_dispatch_table_for_class (object->class_pointer,
object->class_pointer);
dtable = __objc_dispatch_table (object->class_pointer);
}
dtable = __objc_prepared_dtable_for_class (object->class_pointer);
assert (dtable);
}
else
dtable = object->class_pointer->dtable;
objc_mutex_unlock (__objc_runtime_mutex);
}
@ -342,27 +264,34 @@ objc_msg_lookup (id receiver, SEL op)
(sidx)op->sel_id);
if (result == 0)
{
Class class = receiver->class_pointer;
struct sarray *dtable;
if ((dtable = class->dtable) == __objc_uninstalled_dtable)
{
/* 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. */
/* Not a valid method */
if (receiver->class_pointer->dtable == __objc_uninstalled_dtable)
{
objc_mutex_lock (__objc_runtime_mutex);
dtable = __objc_dispatch_table (class);
if (dtable == __objc_uninstalled_dtable)
if (receiver->class_pointer->dtable == __objc_uninstalled_dtable)
{
/* The dispatch table needs to be installed.
This happens on the very first method call to the class. */
__objc_init_install_dtable (receiver, op);
This happens on the very first method call to the
class. */
__objc_install_dtable_for_class (receiver->class_pointer);
/* If we can get the implementation from the newly installed
dtable, +initialize has completed. */
result = get_imp (receiver->class_pointer, op);
/* If not, messages are being sent during +initialize and
we should dispatch them without the installed dtable.
In this case we have locked the mutex recursively
so execution remains in this thread after our unlock. */
if (result == 0
&& (receiver->class_pointer->dtable
== __objc_uninstalled_dtable))
result
= __objc_get_prepared_imp (receiver->class_pointer, op);
}
objc_mutex_unlock (__objc_runtime_mutex);
/* Get real method for this in newly installed dtable */
result = get_imp (class, op);
objc_mutex_unlock (__objc_runtime_mutex);
}
else
{
@ -416,55 +345,6 @@ __objc_init_dispatch_tables ()
__objc_uninstalled_dtable = sarray_new (200, 0);
}
/* This function is called by objc_msg_lookup when the
dispatch table needs to be installed; thus it is called once
for each class, namely when the very first message is sent to it. */
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 (__objc_dispatch_table (receiver->class_pointer)
!= __objc_uninstalled_dtable)
{
objc_mutex_unlock (__objc_runtime_mutex);
return;
}
if (CLS_ISCLASS (receiver->class_pointer))
{
/* receiver is an ordinary object */
assert (CLS_ISCLASS (receiver->class_pointer));
/* install instance methods table */
__objc_begin_install_dispatch_table_for_class
(receiver->class_pointer, receiver->class_pointer);
/* call +initialize -- this will in turn install the factory
dispatch table if not already done :-) */
__objc_send_initialize (receiver->class_pointer);
__objc_end_install_dispatch_table_for_class (receiver->class_pointer);
}
else
{
/* receiver is a class object */
assert (CLS_ISCLASS ((Class)receiver));
assert (CLS_ISMETA (receiver->class_pointer));
/* Install real dtable for factory methods */
__objc_begin_install_dispatch_table_for_class
(receiver->class_pointer, (Class)receiver);
__objc_send_initialize ((Class)receiver);
__objc_end_install_dispatch_table_for_class (receiver->class_pointer);
}
objc_mutex_unlock (__objc_runtime_mutex);
}
/* Install dummy table for class which causes the first message to
that class (or instances hereof) to be initialized properly */
void
@ -482,6 +362,9 @@ __objc_send_initialize (Class class)
assert (CLS_ISCLASS (class));
assert (! CLS_ISMETA (class));
/* class_add_method_list/__objc_update_dispatch_table_for_class
may have reset the dispatch table. The canonical way to insure
that we send +initialize just once, is this flag. */
if (! CLS_ISINITIALIZED (class))
{
CLS_SETINITIALIZED (class);
@ -490,6 +373,9 @@ __objc_send_initialize (Class class)
/* Create the garbage collector type memory description */
__objc_generate_gc_type_description (class);
if (class->super_class)
__objc_send_initialize (class->super_class);
{
SEL op = sel_register_name ("initialize");
IMP imp = 0;
@ -528,8 +414,7 @@ __objc_send_initialize (Class class)
method nothing is guaranteed about what method will be used.
Assumes that __objc_runtime_mutex is locked down. */
static void
__objc_install_methods_in_dtable (struct sarray *dtable,
MethodList_t method_list)
__objc_install_methods_in_dtable (struct sarray *dtable, MethodList_t method_list)
{
int i;
@ -537,9 +422,7 @@ __objc_install_methods_in_dtable (struct sarray *dtable,
return;
if (method_list->method_next)
{
__objc_install_methods_in_dtable (dtable, method_list->method_next);
}
__objc_install_methods_in_dtable (dtable, method_list->method_next);
for (i = 0; i < method_list->method_count; i++)
{
@ -550,136 +433,37 @@ __objc_install_methods_in_dtable (struct sarray *dtable,
}
}
/* Assumes that __objc_runtime_mutex is locked down.
* If receiver is not null, it is the object whos supercalss must be
* initialised if the superclass of the one we are installing the
* dispatch table for is not already installed.
*/
static void
__objc_begin_install_dispatch_table_for_class (Class class, Class receiver)
{
struct sarray *dtable;
Class super;
/* If the class has not yet had its class links resolved, we must
re-compute all class links */
if (! CLS_ISRESOLV (class))
__objc_resolve_class_links ();
super = class->super_class;
/* If the superclass has not had its dispatch table installed,
* we must do that (and send +initialize to it).
*/
if (super != 0 && __objc_dispatch_table(super) == __objc_uninstalled_dtable)
{
__objc_begin_install_dispatch_table_for_class
(super, receiver->super_class);
if (CLS_ISMETA (super))
{
/* super is a metaclass, so we must send +initialize to the
* superclass of the receiver.
*/
__objc_send_initialize (receiver->super_class);
}
else
{
/* super is a class and must therefore receive +initialize
*/
__objc_send_initialize (super);
}
__objc_end_install_dispatch_table_for_class (super);
}
/* Allocate dtable if necessary */
if (super == 0)
{
dtable = sarray_new (__objc_selector_max_index, 0);
}
else
{
dtable = sarray_lazy_copy (__objc_dispatch_table (super));
}
__objc_install_methods_in_dtable (dtable, class->methods);
__objc_set_initializing_dispatch_table(class, dtable);
}
/* Assumes that __objc_runtime_mutex is locked down.
* The __objc_begin_install_dispatch_table_for_class() function must have run.
*/
static void
__objc_end_install_dispatch_table_for_class (Class class)
{
class->dtable = __objc_dispatch_table (class);
__objc_set_initializing_dispatch_table(class, 0);
}
/* Assumes that __objc_runtime_mutex is locked down.
*/
static void
__objc_install_dispatch_table_for_class (Class class, Class receiver)
{
if (__objc_is_initializing_dispatch_table(class))
{
struct sarray *dtable;
Class super = class->super_class;
/* Already in the process of installing/initialising the dispatch
* table, so we can assume that the code which started the process
* will also end it, and all we need to do is update the table now.
*/
if (super == 0)
{
dtable = sarray_new (__objc_selector_max_index, 0);
}
else
{
dtable = sarray_lazy_copy (__objc_dispatch_table (super));
}
__objc_install_methods_in_dtable (dtable, class->methods);
__objc_set_initializing_dispatch_table(class, dtable);
}
else
{
__objc_begin_install_dispatch_table_for_class (class, receiver);
__objc_end_install_dispatch_table_for_class (class);
}
}
void
__objc_update_dispatch_table_for_class (Class class)
{
Class next;
struct sarray *arr;
objc_mutex_lock (__objc_runtime_mutex);
/* not yet installed -- skip it */
if ((arr = __objc_dispatch_table (class)) == __objc_uninstalled_dtable)
/* not yet installed -- skip it unless in +initialize */
if (class->dtable == __objc_uninstalled_dtable)
{
if (__objc_prepared_dtable_for_class (class))
{
/* There is a prepared table so we must be initialising this
class ... we must re-do the table preparation. */
__objc_prepare_dtable_for_class (class);
}
objc_mutex_unlock (__objc_runtime_mutex);
return;
}
if (__objc_is_initializing_dispatch_table(class) == 0)
{
__objc_install_premature_dtable (class); /* someone might require it... */
}
arr = class->dtable;
__objc_install_premature_dtable (class); /* someone might require it... */
sarray_free (arr); /* release memory */
/* could have been lazy... */
__objc_install_dispatch_table_for_class (class, 0);
__objc_install_dtable_for_class (class);
if (class->subclass_list) /* Traverse subclasses */
{
Class next;
for (next = class->subclass_list; next; next = next->sibling_class)
{
__objc_update_dispatch_table_for_class (next);
}
}
for (next = class->subclass_list; next; next = next->sibling_class)
__objc_update_dispatch_table_for_class (next);
objc_mutex_unlock (__objc_runtime_mutex);
}
@ -925,3 +709,222 @@ objc_get_uninstalled_dtable ()
{
return __objc_uninstalled_dtable;
}
static cache_ptr prepared_dtable_table = 0;
/* This function is called by:
objc_msg_lookup, get_imp and __objc_responds_to
(and the dispatch table installation functions themselves)
to install a dispatch table for a class.
If CLS is a class, it installs instance methods.
If CLS is a meta class, it installs class methods.
In either case +initialize is invoked for the corresponding class.
The implementation must insure that the dispatch table is not
installed until +initialize completes. Otherwise it opens a
potential race since the installation of the dispatch table is
used as gate in regular method dispatch and we need to guarantee
that +initialize is the first method invoked an that no other
thread my dispatch messages to the class before +initialize
completes.
*/
static void
__objc_install_dtable_for_class (Class cls)
{
/* If the class has not yet had its class links resolved, we must
re-compute all class links */
if (! CLS_ISRESOLV (cls))
__objc_resolve_class_links ();
/* Make sure the super class has its dispatch table installed
or is at least preparing.
We do not need to send initialize for the super class since
__objc_send_initialize will insure that.
*/
if (cls->super_class
&& cls->super_class->dtable == __objc_uninstalled_dtable
&& !__objc_prepared_dtable_for_class (cls->super_class))
{
__objc_install_dtable_for_class (cls->super_class);
/* The superclass initialisation may have also initialised the
current class, in which case there is no more to do. */
if (cls->dtable != __objc_uninstalled_dtable)
{
return;
}
}
/* We have already been prepared but +initialize hasn't completed.
The +initialize implementation is probably sending 'self' messages.
We rely on _objc_get_prepared_imp to retrieve the implementation
pointers. */
if (__objc_prepared_dtable_for_class (cls))
{
return;
}
/* We have this function cache the implementation pointers
for _objc_get_prepared_imp but the dispatch table won't
be initilized until __objc_send_initialize completes. */
__objc_prepare_dtable_for_class (cls);
/* We may have already invoked +initialize but
__objc_update_dispatch_table_for_class invoked by
class_add_method_list may have reset dispatch table. */
/* Call +initialize.
If we are a real class, we are installing instance methods.
If we are a meta class, we are installing class methods.
The __objc_send_initialize itself will insure that the message
is called only once per class. */
if (CLS_ISCLASS (cls))
__objc_send_initialize (cls);
else
{
/* Retreive the class from the meta class. */
Class c = objc_lookup_class (cls->name);
assert (CLS_ISMETA (cls));
assert (c);
__objc_send_initialize (c);
}
/* We install the dispatch table correctly when +initialize completed. */
__objc_install_prepared_dtable_for_class (cls);
}
/* Builds the dispatch table for the class CLS and stores
it in a place where it can be retrieved by
__objc_get_prepared_imp until __objc_install_prepared_dtable_for_class
installs it into the class.
The dispatch table should not be installed into the class until
+initialize has completed. */
static void
__objc_prepare_dtable_for_class (Class cls)
{
struct sarray *dtable;
struct sarray *super_dtable;
/* This table could be initialized in init.c.
We can not use the class name since
the class maintains the instance methods and
the meta class maintains the the class methods yet
both share the same name.
Classes should be unique in any program. */
if (! prepared_dtable_table)
prepared_dtable_table
= objc_hash_new(32,
(hash_func_type) objc_hash_ptr,
(compare_func_type) objc_compare_ptrs);
/* If the class has not yet had its class links resolved, we must
re-compute all class links */
if (! CLS_ISRESOLV (cls))
__objc_resolve_class_links ();
assert (cls);
assert (cls->dtable == __objc_uninstalled_dtable);
/* If there is already a prepared dtable for this class, we must replace
it with a new version (since there must have been methods added to or
otherwise modified in the class while executing +initialize, and the
table needs to be recomputed. */
dtable = __objc_prepared_dtable_for_class (cls);
if (0 != dtable)
{
objc_hash_remove (prepared_dtable_table, cls);
sarray_free (dtable);
}
/* Now prepare the dtable for population. */
assert (cls != cls->super_class);
if (cls->super_class)
{
/* Inherit the method list from the super class.
Yet the super class may still be initializing
in the case when a class cluster sub class initializes
its super classes. */
if (cls->super_class->dtable == __objc_uninstalled_dtable)
__objc_install_dtable_for_class (cls->super_class);
super_dtable = cls->super_class->dtable;
/* If the dispatch table is not yet installed,
we are still in the process of executing +initialize.
Yet the dispatch table should be available. */
if (super_dtable == __objc_uninstalled_dtable)
super_dtable = __objc_prepared_dtable_for_class (cls->super_class);
assert (super_dtable);
dtable = sarray_lazy_copy (super_dtable);
}
else
dtable = sarray_new (__objc_selector_max_index, 0);
__objc_install_methods_in_dtable (dtable, cls->methods);
objc_hash_add (&prepared_dtable_table,
cls,
dtable);
}
/* This wrapper only exists to allow an easy replacement of
the lookup implementation and it is expected that the compiler
will optimize it away. */
static struct sarray *
__objc_prepared_dtable_for_class (Class cls)
{
struct sarray *dtable = 0;
assert (cls);
if (prepared_dtable_table)
dtable = objc_hash_value_for_key (prepared_dtable_table, cls);
/* dtable my be nil,
since we call this to check whether we are currently preparing
before we start preparing. */
return dtable;
}
/* Helper function for messages sent to CLS or implementation pointers
retrieved from CLS during +initialize before the dtable is installed.
When a class implicitly initializes another class which in turn
implicitly invokes methods in this class, before the implementation of
+initialize of CLS completes, this returns the expected implementation.
Forwarding remains the responsibility of objc_msg_lookup.
This function should only be called under the global lock.
*/
static IMP
__objc_get_prepared_imp (Class cls,SEL sel)
{
struct sarray *dtable;
IMP imp;
assert (cls);
assert (sel);
assert (cls->dtable == __objc_uninstalled_dtable);
dtable = __objc_prepared_dtable_for_class (cls);
assert (dtable);
assert (dtable != __objc_uninstalled_dtable);
imp = sarray_get_safe (dtable, (size_t) sel->sel_id);
/* imp may be Nil if the method does not exist and we
may fallback to the forwarding implementation later. */
return imp;
}
/* When this function is called +initialize should be completed.
So now we are safe to install the dispatch table for the
class so that they become available for other threads
that may be waiting in the lock.
*/
static void
__objc_install_prepared_dtable_for_class (Class cls)
{
assert (cls);
assert (cls->dtable == __objc_uninstalled_dtable);
cls->dtable = __objc_prepared_dtable_for_class (cls);
assert (cls->dtable);
assert (cls->dtable != __objc_uninstalled_dtable);
objc_hash_remove (prepared_dtable_table, cls);
}

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