Example explanation of block circular reference problem under iOS MRC

  //Note that this __block will copy a pointer. If the original pointer is set to nil, the pointer copied here will be a wild pointer.    __block __typeof(self)weakSelf = self; 
    //__weak __typeof(self)weakSelf = self; 
    //__weak Person *weakSelf = self; 
    void (^block)(void) = ^(void){ 
      //NSLog(@"name --> is %@", ); 
      //NSLog(@"name --> is %@", ); 
      //This will make it crash. At this time, weakSelf is a wild pointer.      //weakSelf is a wild pointer at this time.  .  .  Wild pointers are also targeted, right?  Anyway, this wild pointer is not NULL, although the memory it points to is not used for,      //However, the code doesn't know.  Therefore, executing [weakSelf doSomething] will inevitably crash.      //Note that this __block will copy a pointer. If the original pointer is set to nil, the pointer copied here will be a wild pointer.//      if (weakSelf) { 
//        NSLog(@"name --> is %@", ); 
//      } 
      //malloc(22); 
//      malloc_zon 
      //This is of no use.  .  .  weakSelf is already a wild pointer, still crash//      __strong __typeof(weakSelf) strongSelf = weakSelf; 
//      if (weakSelf) { 
//        NSLog(@"name --> is %@", ); 
//      } 
      if (malloc_zone_from_ptr(weakSelf)) { 
        NSLog(@"name --> is %@", ); 
      } 

// 
//  
// test_mrc_block_self_01 
// 
// Created by jeffasd on 2017/12/1. 
// Copyright © 2017 jeffasd. All rights reserved.// 
#import "" 
#import "" 
@interface ViewController () 
@property (nonatomic, copy) NSString *name; 
@end 
@implementation ViewController 
- (void)viewDidLoad { 
  [super viewDidLoad]; 
   = [UIColor whiteColor]; 
   = @"xiaoming"; 
} 
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{ 
   = [UIColor cyanColor]; 
//  void (^block)(void) = ^(void){ 
//    NSLog(@"name --> is %@", ); 
//  }; 
//   
//   
//   
//  for (int i = 0; i < 30; i++) { 
//    block(); 
//  } 
  Person *xiaoming = [[Person alloc] init]; 
  //[xiaoming retain]; 
  [xiaoming release]; 
//  xiaoming = nil; 
  xiaoming = NULL; 
} 
- (void)didReceiveMemoryWarning { 
  [super didReceiveMemoryWarning]; 
  // Dispose of any resources that can be recreated. 
} 
@end 

// 
//  
// test_mrc_block_self_01 
// 
// Created by jeffasd on 2017/12/1. 
// Copyright © 2017 jeffasd. All rights reserved.// 
#import "" 
#include <malloc/> 
@interface Person () 
@property (nonatomic, copy) NSString *name; 
@end 
@implementation Person 
- (instancetype)init{ 
  if (self = [super init]) { 
     = @"xiaoming"; 
    //Note that this __block will copy a pointer. If the original pointer is set to nil, the pointer copied here will be a wild pointer.    __block __typeof(self)weakSelf = self; 
    //__weak __typeof(self)weakSelf = self; 
    //__weak Person *weakSelf = self; 
    void (^block)(void) = ^(void){ 
      //NSLog(@"name --> is %@", ); 
      //NSLog(@"name --> is %@", ); 
      //This will make it crash. At this time, weakSelf is a wild pointer.      //weakSelf is a wild pointer at this time.  .  .  Wild pointers are also targeted, right?  Anyway, this wild pointer is not NULL, although the memory it points to is not used for,      //However, the code doesn't know.  Therefore, executing [weakSelf doSomething] will inevitably crash.      //Note that this __block will copy a pointer. If the original pointer is set to nil, the pointer copied here will be a wild pointer.//      if (weakSelf) { 
//        NSLog(@"name --> is %@", ); 
//      } 
      //malloc(22); 
//      malloc_zon 
      //This is of no use.  .  .  weakSelf is already a wild pointer, still crash//      __strong __typeof(weakSelf) strongSelf = weakSelf; 
//      if (weakSelf) { 
//        NSLog(@"name --> is %@", ); 
//      } 
      if (malloc_zone_from_ptr(weakSelf)) { 
        NSLog(@"name --> is %@", ); 
      } 
    }; 
    for (int i = 0; i < 300; i++) { 
//      dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ 
//        block(); 
//      }); 
      dispatch_async(dispatch_get_main_queue(), ^{ 
        block(); 
      }); 
    } 
  } 
  return self; 
} 
@end