oc的内存管理

@implementation Dog(void)dealloc{  NSLog(@"Dog 被销毁了");  [super dealloc];}@end@class Dog;@interface Person : NSObject@property(retain) Dog *dog;@endint main(int argc, const char * argv[]) {  Person *p1 = [[Person alloc] init];  Person *p2 = [[Person alloc] init];  Dog *d = [[Dog alloc] init];  p1.dog = d;  p2.dog = d;  [d release];  p1.dog = nil;  p2.dog = nil;  return 0;}//Dog *d被销毁了int main(int argc, const char * argv[]) {  Person *p1 = [[Person alloc] init];  Person *p2 = [[Person alloc] init];  Dog *d = [[Dog alloc] init];  p1.dog = d;  p2.dog = p1.dog;  // 只改了这一行  [d release];  p1.dog = nil;  p2.dog = nil;  return 0;}//Dog *d没有被销毁

dog属性公告为了atomic类型，为了保证原子性，dog的set和get方法应该做过解决。我感觉mrc下的atomic属性的set和get方法应该如下

- (Dog *) dog {    Dog *d = nil;     @synchronized(self) {        d = [[_dog retain] autorelease];    }     return d;}- (void)setDog:(Dog *)dog {    @synchronized(self) {        [dog retain];        [_dog release];        _dog = dog;    }}

所以在调用p2.dog = p1.dog；的时候会先调用p1.dog的get方法，内部会对dog retain一次，引用计数+1，而后放进自动释放池，再调用p2.dog的set方法，又会retain一次。最后release的时候-1，引用计数最后依然是1，所以不会被释放