registered to be copied on heap assignment. By default, this is just
_NSConcreteStackBlock. Other classes can be registered (LanguageKit should
register BlockClosure to make sure that Smalltalk works).
Fred: This makes the stuff that we discussed briefly at FOSDEM possible in GC
mode: We can allocate a GSStackEvent subclass of NSEvent on the stack. If it
implements a -copy method that returns an NSEvent and is registered with the
runtime in this way, then any code that assigns it anywhere on the heap will
end up implicitly creating a heap copy.
- Add objc_gc_collectable_address() to determine whether a pointer is managed
by the GC
- If LIBOBJC_CANARIES is set (optionally to a random number seed) then store a
canary value after every allocation returned by
objc_gc_allocate_collectable() and, when it is finalised, check that the
canary has not been modified, aborting if it has. This catches some
heap-buffer overflows, and currently causes GNUstep to abort.
- If LIBOBJC_LOG_ALLOCATIONS is set to a file name, log all GC-managed
allocations to that file. This gives something like malloc_history on OS X.
- objc_memmove_collectable() now guarantees that all copied pointers remain
visible to the GC at all times (which was the point of the function - the
original implementation was just a quick stub).
theraven