@implementation Dog
(void)dealloc
{
NSLog(@"Dog 被销毁了");
[super dealloc];
}
@end
@class Dog;
@interface Person : NSObject
@property(retain) Dog *dog;
@end
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 = 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属性声明为了atomic类型，为了保证原子性，dog的set和get方法应该做过处理。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，然后放进自动释放池，再调用p2.dog的set方法，又会retain一次。最后release的时候-1，引用计数最后仍然是1，所以不会被释放
