/* * Copyright (c) 2010-2011 Apple Inc. All rights reserved. * * @APPLE_LICENSE_HEADER_START@ * * This file contains Original Code and/or Modifications of Original Code * as defined in and that are subject to the Apple Public Source License * Version 2.0 (the 'License'). You may not use this file except in * compliance with the License. Please obtain a copy of the License at * http://www.opensource.apple.com/apsl/ and read it before using this * file. * * The Original Code and all software distributed under the License are * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. * Please see the License for the specific language governing rights and * limitations under the License. * * @APPLE_LICENSE_HEADER_END@ */ #ifndef _OBJC_WEAK_H_ #define _OBJC_WEAK_H_ #include <objc/objc.h> #include "objc-config.h" __BEGIN_DECLS /* The weak table is a hash table governed by a single spin lock. An allocated blob of memory, most often an object, but under GC any such allocation, may have its address stored in a __weak marked storage location through use of compiler generated write-barriers or hand coded uses of the register weak primitive. Associated with the registration can be a callback block for the case when one of the allocated chunks of memory is reclaimed. The table is hashed on the address of the allocated memory. When __weak marked memory changes its reference, we count on the fact that we can still see its previous reference. So, in the hash table, indexed by the weakly referenced item, is a list of all locations where this address is currently being stored. For ARR, we also keep track of whether an arbitrary object is being deallocated by briefly placing it in the table just prior to invoking dealloc, and removing it via objc_clear_deallocating just prior to memory reclamation. */ /// The address of a __weak object reference typedef id * weak_referrer_t; #if __LP64__ #define PTR_MINUS_1 63 #else #define PTR_MINUS_1 31 #endif /** * The internal structure stored in the weak references table. * It maintains and stores * a hash set of weak references pointing to an object. * If out_of_line==0, the set is instead a small inline array. */ #define WEAK_INLINE_COUNT 4 struct weak_entry_t { id referent; union { struct { weak_referrer_t *referrers; uintptr_t out_of_line : 1; uintptr_t num_refs : PTR_MINUS_1; uintptr_t mask; uintptr_t max_hash_displacement; }; struct { // out_of_line=0 is LSB of one of these (don't care which) weak_referrer_t inline_referrers[WEAK_INLINE_COUNT]; }; }; }; /** * The global weak references table. Stores object ids as keys, * and weak_entry_t structs as their values. */ struct weak_table_t { weak_entry_t *weak_entries; size_t num_entries; uintptr_t mask; uintptr_t max_hash_displacement; }; /// Adds an (object, weak pointer) pair to the weak table. id weak_register_no_lock(weak_table_t *weak_table, id referent, id *referrer); /// Removes an (object, weak pointer) pair from the weak table. void weak_unregister_no_lock(weak_table_t *weak_table, id referent, id *referrer); /// Assert a weak pointer is valid and retain the object during its use. id weak_read_no_lock(weak_table_t *weak_table, id *referrer); /// Called on object destruction. Sets all remaining weak pointers to nil. void weak_clear_no_lock(weak_table_t *weak_table, id referent); __END_DECLS #endif /* _OBJC_WEAK_H_ */