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290 lines
9.2 KiB
Objective-C
290 lines
9.2 KiB
Objective-C
/* GNU Objective C Runtime accessors functions
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Copyright (C) 2010-2020 Free Software Foundation, Inc.
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Contributed by Nicola Pero
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it under the
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terms of the GNU General Public License as published by the Free Software
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Foundation; either version 3, or (at your option) any later version.
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GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
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details.
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Under Section 7 of GPL version 3, you are granted additional
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permissions described in the GCC Runtime Library Exception, version
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3.1, as published by the Free Software Foundation.
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You should have received a copy of the GNU General Public License and
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a copy of the GCC Runtime Library Exception along with this program;
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see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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<http://www.gnu.org/licenses/>. */
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#include "objc-private/common.h"
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#include "objc/objc.h"
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#include "objc/thr.h"
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#include <string.h> /* For memcpy */
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/* This file contains functions that the compiler uses when
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synthesizing accessors (getters/setters) for properties. The
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functions are part of the ABI, but are meant to be used by the
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compiler and not by users; for this reason, they are not declared
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in public header files. The compiler automatically generates
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declarations for these functions. */
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/* Properties can be "atomic", which requires protecting them from
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concurrency issues using a lock. Unfortunately, we can't have a
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lock for each property, so we'll go with a small pool of locks.
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Any time a property is accessed in an "atomic" way, we pick a
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random lock from the pool (random, but always the same one for the
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same property of the same object) and use it to protect access to
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the property.
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The size of the pool is currently 16. A bigger pool can help
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reduce contention, ie, reduce the chances that two threads,
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operating on unrelated properties, will have to wait for each other
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because the properties use the same lock. 16 seems big enough at
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the moment. */
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#define ACCESSORS_NUMBER_OF_LOCKS 16
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#define ACCESSORS_HASH(POINTER) ((((size_t)POINTER >> 8) ^ (size_t)POINTER) & (ACCESSORS_NUMBER_OF_LOCKS - 1))
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static objc_mutex_t accessors_locks[ACCESSORS_NUMBER_OF_LOCKS];
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/* This is called at startup to setup the locks. */
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void
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__objc_accessors_init (void)
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{
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int i;
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for (i = 0; i < ACCESSORS_NUMBER_OF_LOCKS; i++)
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accessors_locks[i] = objc_mutex_allocate ();
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}
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/* The property accessors automatically call various methods from the
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Foundation library (eg, GNUstep-base). These methods are not
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implemented here, but we need to declare them so we can compile the
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runtime. The Foundation library will need to provide
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implementations of these methods (most likely in the root class,
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eg, NSObject) as the accessors only work with objects of classes
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that implement these methods. */
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@interface _libobjcNSObject
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- (id) copyWithZone: (void *)zone;
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- (id) mutableCopyWithZone: (void *)zone;
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@end
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#define COPY(X) [((_libobjcNSObject *)(X)) copyWithZone: NULL]
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#define MUTABLE_COPY(X) [((_libobjcNSObject *)(X)) mutableCopyWithZone: NULL]
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#if OBJC_WITH_GC
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# define AUTORELEASE(X) (X)
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# define RELEASE(X)
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# define RETAIN(X) (X)
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#else
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@interface _libobjcNSObject (RetainReleaseMethods)
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- (id) autorelease;
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- (oneway void) release;
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- (id) retain;
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@end
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# define AUTORELEASE(X) [((_libobjcNSObject *)(X)) autorelease]
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# define RELEASE(X) [((_libobjcNSObject *)(X)) release]
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# define RETAIN(X) [((_libobjcNSObject *)(X)) retain]
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#endif
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/* The compiler uses this function when implementing some synthesized
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getters for properties of type 'id'. */
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id
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objc_getProperty (id self, SEL __attribute__((unused)) _cmd, ptrdiff_t offset, BOOL is_atomic)
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{
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if (self != nil)
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{
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id *pointer_to_ivar = (id *)((char *)self + offset);
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if (is_atomic == NO)
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{
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/* Note that in this case, we do not RETAIN/AUTORELEASE the
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returned value. The programmer should do it if it is
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needed. Since access is non-atomic, other threads can be
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ignored and the caller has full control of what happens
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to the object and whether it needs to be RETAINed or not,
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so it makes sense to leave the decision to him/her. This
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is also what the Apple/NeXT runtime does. */
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return *pointer_to_ivar;
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}
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else
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{
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objc_mutex_t lock = accessors_locks[ACCESSORS_HASH (pointer_to_ivar)];
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id result;
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objc_mutex_lock (lock);
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result = RETAIN (*(pointer_to_ivar));
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objc_mutex_unlock (lock);
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return AUTORELEASE (result);
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}
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}
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return nil;
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}
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/* The compiler uses this function when implementing some synthesized
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setters for properties of type 'id'.
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PS: Note how 'should_copy' is declared 'BOOL' but then actually
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takes values from 0 to 2. This hack was introduced by Apple; we
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do the same for compatibility reasons. */
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void
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objc_setProperty (id self, SEL __attribute__((unused)) _cmd, ptrdiff_t offset, id new_value, BOOL is_atomic, BOOL should_copy)
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{
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if (self != nil)
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{
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id *pointer_to_ivar = (id *)((char *)self + offset);
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id retained_value;
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#if !OBJC_WITH_GC
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id old_value;
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#endif
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switch (should_copy)
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{
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case 0: /* retain */
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{
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if (*pointer_to_ivar == new_value)
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return;
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retained_value = RETAIN (new_value);
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break;
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}
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case 2: /* mutable copy */
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{
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retained_value = MUTABLE_COPY (new_value);
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break;
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}
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case 1: /* copy */
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default:
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{
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retained_value = COPY (new_value);
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break;
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}
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}
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if (is_atomic == NO)
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{
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#if !OBJC_WITH_GC
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old_value = *pointer_to_ivar;
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#endif
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*pointer_to_ivar = retained_value;
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}
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else
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{
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objc_mutex_t lock = accessors_locks[ACCESSORS_HASH (pointer_to_ivar)];
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objc_mutex_lock (lock);
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#if !OBJC_WITH_GC
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old_value = *pointer_to_ivar;
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#endif
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*pointer_to_ivar = retained_value;
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objc_mutex_unlock (lock);
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}
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#if !OBJC_WITH_GC
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RELEASE (old_value);
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#endif
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}
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}
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/* The compiler uses this function when implementing some synthesized
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getters for properties of arbitrary C types. The data is just
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copied. Compatibility Note: this function does not exist in the
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Apple/NeXT runtime. */
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void
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objc_getPropertyStruct (void *destination, const void *source, ptrdiff_t size, BOOL is_atomic, BOOL __attribute__((unused)) has_strong)
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{
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if (is_atomic == NO)
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memcpy (destination, source, size);
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else
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{
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objc_mutex_t lock = accessors_locks[ACCESSORS_HASH (source)];
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objc_mutex_lock (lock);
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memcpy (destination, source, size);
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objc_mutex_unlock (lock);
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}
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}
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/* The compiler uses this function when implementing some synthesized
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setters for properties of arbitrary C types. The data is just
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copied. Compatibility Note: this function does not exist in the
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Apple/NeXT runtime. */
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void
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objc_setPropertyStruct (void *destination, const void *source, ptrdiff_t size, BOOL is_atomic, BOOL __attribute__((unused)) has_strong)
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{
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if (is_atomic == NO)
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memcpy (destination, source, size);
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else
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{
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objc_mutex_t lock = accessors_locks[ACCESSORS_HASH (destination)];
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objc_mutex_lock (lock);
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memcpy (destination, source, size);
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objc_mutex_unlock (lock);
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}
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}
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/* This is the function that the Apple/NeXT runtime has instead of
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objc_getPropertyStruct and objc_setPropertyStruct. We include it
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for API compatibility (just for people who may have used
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objc_copyStruct on the NeXT runtime thinking it was a public API);
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the compiler never generates calls to it with the GNU runtime.
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This function is clumsy because it requires two locks instead of
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one. */
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void
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objc_copyStruct (void *destination, const void *source, ptrdiff_t size, BOOL is_atomic, BOOL __attribute__((unused)) has_strong)
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{
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if (is_atomic == NO)
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memcpy (destination, source, size);
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else
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{
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/* We don't know which one is the property, so we have to lock
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both. One of them is most likely a temporary buffer in the
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local stack and we really wouldn't want to lock it (our
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objc_getPropertyStruct and objc_setPropertyStruct functions
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don't lock it). Note that if we're locking more than one
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accessor lock at once, we need to always lock them in the
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same order to avoid deadlocks. */
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objc_mutex_t first_lock;
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objc_mutex_t second_lock;
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if (ACCESSORS_HASH (source) == ACCESSORS_HASH (destination))
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{
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/* A lucky collision. */
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first_lock = accessors_locks[ACCESSORS_HASH (source)];
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objc_mutex_lock (first_lock);
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memcpy (destination, source, size);
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objc_mutex_unlock (first_lock);
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return;
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}
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if (ACCESSORS_HASH (source) > ACCESSORS_HASH (destination))
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{
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first_lock = accessors_locks[ACCESSORS_HASH (source)];
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second_lock = accessors_locks[ACCESSORS_HASH (destination)];
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}
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else
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{
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first_lock = accessors_locks[ACCESSORS_HASH (destination)];
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second_lock = accessors_locks[ACCESSORS_HASH (source)];
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}
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objc_mutex_lock (first_lock);
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objc_mutex_lock (second_lock);
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memcpy (destination, source, size);
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objc_mutex_unlock (second_lock);
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objc_mutex_unlock (first_lock);
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}
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}
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