__block在MRC ARC下的區別

研究下__block在MRC/ARC下區別，直接上代碼。

@property (nonatomic,copy) TestBlock   block;//定義的block

一._NSConcreteStackBlock

- (void)stackBlock{

    NSLog(@"stackBlock start....");

    Person *person = [[Person alloc]init];person.personName = @"張三";

    NSLog(@"person RetainCount is %ld", CFGetRetainCount((__bridge CFTypeRef)person));

    __block  Person *blockPerson = person;

    NSLog(@"blockPerson RetainCount is %ld", CFGetRetainCount((__bridge CFTypeRef)blockPerson));

    void (^block)(int a) = ^(int a){

        NSLog(@"block blockPerson 111   is %ld", CFGetRetainCount((__bridge CFTypeRef)blockPerson));

        NSLog(@"block person 111  is %ld", CFGetRetainCount((__bridge CFTypeRef)person));

　　NSLog(@"block self  is %ld", CFGetRetainCount((__bridge CFTypeRef)self));

    };

    NSLog(@"block is %@",block);

    block(2);

    NSLog(@"block blockPerson 2222 is %ld", CFGetRetainCount((__bridge CFTypeRef)blockPerson));

    NSLog(@"block person 222 is %ld", CFGetRetainCount((__bridge CFTypeRef)person));

#if !__has_feature(objc_arc)

    [person release];

#endif

    NSLog(@"stackBlock end....\r\n\r\n\r\n\r\n");

}

日誌

MRC

2016-03-17 16:32:25.253 ARCAndMRC[12313:228133] stackBlock start....

2016-03-17 16:32:25.254 ARCAndMRC[12313:228133] person RetainCount is 1

2016-03-17 16:32:25.254 ARCAndMRC[12313:228133] blockPerson RetainCount is 1

2016-03-17 16:32:25.254 ARCAndMRC[12313:228133] block is <__NSStackBlock__: 0xbff9c100>

2016-03-17 16:32:25.254 ARCAndMRC[12313:228133] block blockPerson 111   is 1

2016-03-17 16:32:25.254 ARCAndMRC[12313:228133] block person 111  is 1

2016-03-17 16:32:25.254 ARCAndMRC[12313:228133] block blockPerson 2222 is 1

2016-03-17 16:32:25.254 ARCAndMRC[12313:228133] block person 222 is 1

2016-03-17 16:32:25.254 ARCAndMRC[12313:228133] Person release ..:張三

2016-03-17 16:32:25.255 ARCAndMRC[12313:228133] stackBlock end....

ARC下

2016-03-17 17:14:22.662 ARCAndMRC[13677:260528] stackBlock start....

2016-03-17 17:14:22.663 ARCAndMRC[13677:260528] person RetainCount is 1

2016-03-17 17:14:22.663 ARCAndMRC[13677:260528] blockPerson RetainCount is 2

2016-03-17 17:14:22.663 ARCAndMRC[13677:260528] block is <__NSMallocBlock__: 0x7c92cf40>

2016-03-17 17:14:22.663 ARCAndMRC[13677:260528] block blockPerson 111   is 4

2016-03-17 17:14:22.663 ARCAndMRC[13677:260528] block person 111  is 4

2016-03-17 17:14:22.663 ARCAndMRC[13677:260528] block self  is 3

2016-03-17 17:14:22.663 ARCAndMRC[13677:260528] block blockPerson 2222 is 4

2016-03-17 17:14:22.663 ARCAndMRC[13677:260528] block person 222 is 4

2016-03-17 17:14:22.664 ARCAndMRC[13677:260528] stackBlock end....

2016-03-17 17:14:22.664 ARCAndMRC[13677:260528] Person release ..:張三

根據日誌能夠看出,MRC下__block修飾的變量，並不改變引用計數,同時block內部並不對引入的外部對象，更改引用計數。

ARC下block會被修改成__NSMallocBlock__ ,同時引用計數增長了。

 

2._NSConcreteMallocBlock

- (void)mallocStack{

    NSLog(@"mallocStack start....");

    Person *person = [[Person alloc]init];person.personName = @"張三";

    NSLog(@"person RetainCount is %ld", CFGetRetainCount((__bridge CFTypeRef)person));

    __block  Person *blockPerson = person;

     NSLog(@"blockPerson RetainCount is %ld", CFGetRetainCount((__bridge CFTypeRef)blockPerson));

    self.block = ^(int a){

        NSLog(@"block blockPerson 111   is %ld", CFGetRetainCount((__bridge CFTypeRef)blockPerson));

        NSLog(@"block person 111  is %ld", CFGetRetainCount((__bridge CFTypeRef)person));

　　NSLog(@"block self  is %ld", CFGetRetainCount((__bridge CFTypeRef)self));

    };

    NSLog(@"self.block is %@", self.block);

    self.block(2);

    NSLog(@"block blockPerson 2222 is %ld", CFGetRetainCount((__bridge CFTypeRef)blockPerson));

    NSLog(@"block person 222 is %ld", CFGetRetainCount((__bridge CFTypeRef)person));

 #if !__has_feature(objc_arc)

    [person release];

#endif

    NSLog(@"mallocStack end....\r\n\r\n\r\n\r\n");

}

日誌

MRC

2016-03-17 17:27:33.739 ARCAndMRC[14065:269749] mallocStack start....

2016-03-17 17:27:33.739 ARCAndMRC[14065:269749] person RetainCount is 1

2016-03-17 17:27:33.739 ARCAndMRC[14065:269749] blockPerson RetainCount is 1

2016-03-17 17:27:33.739 ARCAndMRC[14065:269749] self.block retaincount is 1 <__NSMallocBlock__: 0x7ae09d30>

2016-03-17 17:27:33.739 ARCAndMRC[14065:269749] block blockPerson 111   is 2

2016-03-17 17:27:33.739 ARCAndMRC[14065:269749] block person 111  is 2

2016-03-17 17:27:33.740 ARCAndMRC[14065:269749] block self  is 2

2016-03-17 17:27:33.740 ARCAndMRC[14065:269749] block blockPerson 2222 is 2

2016-03-17 17:27:33.740 ARCAndMRC[14065:269749] block person 222 is 2

2016-03-17 17:27:33.740 ARCAndMRC[14065:269749] Person release ..:張三

2016-03-17 17:27:33.740 ARCAndMRC[14065:269749] mallocStack end....

ARC

2016-03-17 17:28:45.643 ARCAndMRC[14118:271047] mallocStack start....

2016-03-17 17:28:45.643 ARCAndMRC[14118:271047] person RetainCount is 1

2016-03-17 17:28:45.643 ARCAndMRC[14118:271047] blockPerson RetainCount is 2

2016-03-17 17:28:45.643 ARCAndMRC[14118:271047] self.block retaincount is 1 <__NSMallocBlock__: 0x7b23ed00>

2016-03-17 17:28:45.643 ARCAndMRC[14118:271047] block blockPerson 111   is 4

2016-03-17 17:28:45.644 ARCAndMRC[14118:271047] block person 111  is 4

2016-03-17 17:28:45.644 ARCAndMRC[14118:271047] block self  is 3

2016-03-17 17:28:45.644 ARCAndMRC[14118:271047] block blockPerson 2222 is 4

2016-03-17 17:28:45.644 ARCAndMRC[14118:271047] block person 222 is 4

2016-03-17 17:28:45.644 ARCAndMRC[14118:271047] mallocStack end....

根據日誌能夠看出,MRC下__block修飾的變量，並不改變引用計數,可是block內部對引入的外部對象，會更改引用計數。因此要及時對block進行release.

ARC下，block修飾的引用計數會增長，同時block內部持有的對象引用計數會增長，因此

person沒有被釋放，緣由是block內部持有了self,致使self沒有被釋放，這就會致使循環引用,因此須要使用weak.