1 深拷貝淺拷貝
2 分類(lèi)不能添加成員變量
3 單例標(biāo)準(zhǔn)寫(xiě)法
4 weak弱引用

字符串拷貝分析

// 字符串拷貝分析
   NSString *str = @"testStr";
   NSString *str1 = [str copy];
   NSMutableString *str2 = [str mutableCopy];
   
   NSLog(@"str:%@,%p", str, str);    // str: testStr ,0x10ac23020
   NSLog(@"str1:%@,%p", str1, str1); // str1:testStr ,0x10ac23020
   NSLog(@"str2:%@,%p", str2, str2); // str2:testStr ,0x60000112b720
   // 總結(jié): string不可變字符串 copy淺拷貝 mutableCopy深拷貝
  
   NSMutableString *mutStr = [[NSMutableString alloc] initWithString:@"123"];
   NSString *mutStrCopy = [mutStr copy];
   NSMutableString *mutStrMutCopy = [mutStr mutableCopy];
   
   
   NSLog(@"mutStr:%@,%p", mutStr, mutStr);                      // mutStr:123,       0x6000039cf6c0
   NSLog(@"mutStrCopy:%@,%p", mutStrCopy, mutStrCopy);          // mutStrCopy:123,   0x984f4eaff626b56e
   NSLog(@"mutStrMutCopy:%@,%p", mutStrMutCopy, mutStrMutCopy); // mutStrMutCopy:123,0x6000039ce850
   // 總結(jié): mutableString可變字符串  copy 和 mutableCopy 都是深拷貝
}

屬性字符串深/淺拷貝

@property (nonatomic, strong) NSString* strString;
@property (nonatomic, copy)   NSString* copString;

      NSMutableString* textString = [[NSMutableString alloc] initWithString:@"str"];
      self.strString = textString; // strong
      self.copString = textString; // copy
    
      NSLog(@"\n初始值\ntextSting:%@,\nstrongString:%@,\ncopyString:%@",textString,_strString,_copString);
    /*
     初始值
        textSting:   str,
        strongString:str,
        copyString:  str
     */
      NSLog(@"\n初始內(nèi)存地址\ntextSting:%p,\nstrongString:%p,\ncopyString:%p",textString,_strString,_copString);
    /*
        初始內(nèi)存地址
        textSting:   0x60000198d500,
        strongString:0x60000198d500,
        copyString:  0x9a6b751948ecb1a9   */
      [textString appendString:@"str"];
      NSLog(@"\n修改后值\ntextSting:%@,\nstrongString:%@,\ncopyString:%@",textString,_strString,_copString);
      /*修改后值
       textSting:   strstr,
       strongString:strstr,
       copyString:  str       */
      NSLog(@"\n修改后內(nèi)存地址\ntextSting:%p,\nstrongString:%p,\ncopyString:%p",textString,_strString,_copString);
      /*
       修改后內(nèi)存地址
       textSting:     0x60000198d500,
       strongString:  0x60000198d500,
       copyString:    0x9a6b751948ecb1a9
       */
      /**
       總結(jié): strong 淺拷貝 copy深拷貝
       */

數(shù)組拷貝分析

NSMutableString *testStr = [@"123" mutableCopy];
    // array可變數(shù)組
    NSArray *arr = @[@"1", @"2", testStr];
    // arr = @[@"1", @"2", @"123"]
    NSArray *arrCopy = [arr copy];
    NSMutableArray *arrMutablecopy = [arr mutableCopy];
    
    NSLog(@"===arr:%@,%p \nobjectP:%p", arr, arr, arr[0]); // 原數(shù)組 array
    // arr:(1,    2)       ,0x600002979e60 , objectP:0x10623c168
    NSLog(@"arrCopy:%@,%p \nobjectP:%p", arrCopy, arrCopy, arrCopy[0]); // copy后
    // arr:(1,    2)       ,0x600002979e60 , objectP:0x10623c168
    NSLog(@"arrMutablecopy:%@,%p \nobjectP:%p", arrMutablecopy, arrMutablecopy, arrMutablecopy[0]); // mutableCopy后
    // arrMutablecopy:(1,2),0x60000270a430 , objectP:0x10623c168
    
    // 總結(jié) 不可變數(shù)組, copy淺拷貝, mutableCopy深拷貝
    
    [testStr appendString:@"45"];
    NSLog(@"arr:%@,%p \nobjectP:%p", arr, arr, arr[0]); //原數(shù)組 array 元素修改后
    // arr:(1,    2, 12345)      ,0x600002979e60 , objectP:0x10623c168
    NSLog(@"arrCopy:%@,%p \nobjectP:%p", arrCopy, arrCopy, arrCopy[0]); // copy后
    // arr:(1,    2, 12345)      ,0x600002979e60 , objectP:0x10623c168
    NSLog(@"arrMutablecopy:%@,%p \nobjectP:%p", arrMutablecopy, arrMutablecopy, arrMutablecopy[0]); // mutableCopy后
    // arrMutablecopy:(1,2,12345),0x60000270a430 , objectP:0x10623c168
    
    // 修改元素后總結(jié) 不可變數(shù)組, copy淺拷貝, mutableCopy深拷貝
    
    // 總結(jié) 對(duì)array copy 淺拷貝斟湃，mutableCopy 深拷貝 勿决，但是，mutableCopy后，arrMutablecopy里面的元素 與 原arr里面的元素地址相同骗卜，所以array的mutableCopy是不完全深拷貝峭沦，只深拷貝了第一層跌造，沒(méi)有深拷貝內(nèi)層


    
    /*=============================================================================================*/
    
    
    NSMutableString *mutarrTestStr = [@"abc" mutableCopy];
    // mutableArray 不可變數(shù)組
    NSMutableArray *mutarr = [NSMutableArray arrayWithObjects:@"123", mutarrTestStr, nil];
    // mutarr = @[@"123", @"abc"]
    NSArray *mutarrCopy = [mutarr copy];
    NSMutableArray *mutarrMutablecopy = [mutarr mutableCopy];

    NSLog(@"mutarr:%@,%p \nobjectP:%p", mutarr, mutarr, mutarr[0]); // 原數(shù)組 mutableArray
    // arr:(123,    abc)       ,0x600001396460 , objectP:0x1015bc0e8
    NSLog(@"mutarrCopy:%@,%p \nobjectP:%p", mutarrCopy, mutarrCopy, mutarrCopy[0]); // copy后
    // arr:(123,    abc)       ,0x600001396460 , objectP:0x1015bc0e8
    NSLog(@"mutarrMutablecopy:%@,%p \nobjectP:%p", mutarrMutablecopy, mutarrMutablecopy, mutarrMutablecopy[0]); // mutableCopy后
    // arrMutablecopy:(123,abc),0x60000270a430 , objectP:0x1015bc0e8
    // 總結(jié) 數(shù)組copy 淺拷貝; mutableCopy 深拷貝,  數(shù)組元素淺拷貝(都一樣)
    
    [mutarrTestStr appendString:@"456"]; //數(shù)組 元素修改后
    // mutarr = @[@"123", @"abc456"]
    NSLog(@"mutarr:%@,%p \nobjectP:%p", mutarr, mutarr, mutarr[0]); //原數(shù)組  mutableArray 元素修改后
    // arr:(123,    abc456)       ,0x600001396460 , objectP:0x1015bc0e8
    NSLog(@"mutarrCopy:%@,%p \nobjectP:%p", mutarrCopy, mutarrCopy, mutarrCopy[0]); // copy后
    // arr:(123,    abc456)       ,0x600001396460 , objectP:0x1015bc0e8
    NSLog(@"mutarrMutablecopy:%@,%p \nobjectP:%p", mutarrMutablecopy, mutarrMutablecopy, mutarrMutablecopy[0]);  // mutableCopy后
    // arrMutablecopy:(123,abc456),0x60000270a430 , objectP:0x1015bc0e8
    // 總結(jié) 數(shù)組元素變動(dòng) 和上面地址一樣
    
//   1.對(duì)于不可變對(duì)象而言埠胖，copy便是淺拷貝，mutableCopy是深拷貝
//   2.對(duì)于可變對(duì)象而言笤虫，copy和mutableCopy都是深拷貝旁瘫，但是copy出來(lái)的對(duì)象是不可變的，而mutableCopy出來(lái)的對(duì)象是可變的
//   3. 對(duì)于容器類(lèi)型來(lái)說(shuō)琼蚯，mutableCopy 僅僅拷貝了第一層酬凳，所以是不完全深拷貝

屬性數(shù)組 深/淺拷貝

@property (nonatomic, strong) NSArray* strongArray;
@property (nonatomic, copy)   NSArray* copyedArray;

     // 一 可變數(shù)組
    NSMutableArray *muArray = [NSMutableArray arrayWithArray:@[@"1",@"2",@"3"]];
    self.strongArray = muArray;
    self.copyedArray = muArray;
    NSLog(@"muArray地址:%p,數(shù)據(jù):%@",muArray,muArray);               // muArray地址:    0x600000bafde0, 數(shù)據(jù):(1, 2, 3 )
    NSLog(@"strongArray地址:%p,數(shù)據(jù):%@",_strongArray,_strongArray); // strongArray地址:0x600000bafde0, 數(shù)據(jù):(1, 2, 3 )
    NSLog(@"copyedArray地址:%p,數(shù)據(jù):%@",_copyedArray,_copyedArray); // copyedArray地址:0x600000bafbd0, 數(shù)據(jù):(1, 2, 3 )
    [muArray addObject:@"4"]; // 數(shù)據(jù)修改后
    NSLog(@"muArray地址:%p,數(shù)據(jù):%@",muArray,muArray);                // muArray地址:    0x600000bafde0, 數(shù)據(jù):(1, 2, 3 , 4)
    NSLog(@"strongArray地址:%p,數(shù)據(jù):%@",_strongArray,_strongArray); //  strongArray地址:0x600000bafde0, 數(shù)據(jù):(1, 2, 3 , 4)
    NSLog(@"copyedArray地址:%p,數(shù)據(jù):%@",_copyedArray,_copyedArray); //  copyedArray地址:0x600000bafbd0, 數(shù)據(jù):(1, 2, 3 )
    
   //總結(jié): 可變數(shù)組 賦值: strongArray 淺拷貝 copyedArray 深拷貝
    
    // 二 不可變數(shù)組
    NSArray *array = @[@"1",@"2",@"3"];
    self.strongArray = array;
    self.copyedArray = array;
    NSLog(@"array地址:%p,數(shù)據(jù):%@",array,array);                     // array地址:      0x6000035be340, 數(shù)據(jù):(1, 2, 3 )
    NSLog(@"strongArray地址:%p,數(shù)據(jù):%@",_strongArray,_strongArray); // strongArray地址:0x6000035be340, 數(shù)據(jù):(1, 2, 3 )
    NSLog(@"copyedArray地址:%p,數(shù)據(jù):%@",_copyedArray,_copyedArray); // copyedArray地址:0x6000035be340, 數(shù)據(jù):(1, 2, 3 )
    //總結(jié): 不可變數(shù)組 賦值: strongArray 淺拷貝 copyedArray 淺拷貝

link: http://www.reibang.com/p/7c38856b3231

分類(lèi) 屬性

Objective-C類(lèi)是由Class類(lèi)型來(lái)表示的，它實(shí)際上是一個(gè)指向objc_class結(jié)構(gòu)體的指針凌停。它的定義如下：

typedef struct objc_class *Class;

objc_class結(jié)構(gòu)體的定義如下：

struct objc_class {

    Class isa  OBJC_ISA_AVAILABILITY; // isa指針

#if !__OBJC2__

    Class super_class                                        OBJC2_UNAVAILABLE; // 父類(lèi)

    const char *name                                         OBJC2_UNAVAILABLE; // 類(lèi)名

    long version                                             OBJC2_UNAVAILABLE; // 類(lèi)的版本信息

    long info                                                OBJC2_UNAVAILABLE; // 類(lèi)信息

    long instance_size                                       OBJC2_UNAVAILABLE; // 該類(lèi)的實(shí)例變量大小

    struct objc_ivar_list *ivars                             OBJC2_UNAVAILABLE; // 該類(lèi)的成員變量鏈表

    struct objc_method_list **methodLists                    OBJC2_UNAVAILABLE; // 方法定義的鏈表
    struct objc_cache *cache                                 OBJC2_UNAVAILABLE; // 方法緩存

    struct objc_protocol_list *protocols                     OBJC2_UNAVAILABLE; // 協(xié)議鏈表

#endif
}

為什么不能添加成員變量呢粱年？
在上面的objc_class結(jié)構(gòu)體中，
ivars是objc_ivar_list（成員變量列表）指針罚拟；
methodLists是指向objc_method_list指針的指針台诗。
在Runtime中，objc_class結(jié)構(gòu)體大小是固定的赐俗，long instance_size 標(biāo)識(shí)實(shí)例變量大小,不可能往這個(gè)結(jié)構(gòu)體中添加數(shù)據(jù)拉队，只能修改。所以ivars指向的是一個(gè)固定區(qū)域阻逮，只能修改成員變量值粱快，不能增加成員變量個(gè)數(shù)。methodList是一個(gè)二維數(shù)組叔扼，所以可以修改*methodLists的值來(lái)增加成員方法事哭，雖沒(méi)辦法擴(kuò)展methodLists指向的內(nèi)存區(qū)域，卻可以改變這個(gè)內(nèi)存區(qū)域的值（存儲(chǔ)的是指針）瓜富。因此鳍咱，可以動(dòng)態(tài)添加方法，不能添加成員變量与柑。

link http://www.reibang.com/p/e203d70ccc3f

單例

#import "FTManager.h"

static FTManager *manager = nil;
@implementation FTManager
+ (instancetype)shareManager {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
//        manager = [[FTManager alloc] init];
        manager = [[super allocWithZone:NULL] init] ;
    });
    return manager;
}
// 保證 [[FTManager alloc] init] 對(duì)象地址統(tǒng)一
+ (instancetype)allocWithZone:(struct _NSZone *)zone {
    return [FTManager shareManager];
}
// 保證 [[[FTManager alloc] init] copy] 對(duì)象地址統(tǒng)一
- (nonnull id)copyWithZone:(nullable NSZone *)zone {
    return [FTManager shareManager];
}
@end
    NSLog(@"%p",[FTManager shareManager]);
    NSLog(@"%p",[[FTManager alloc] init]);
    NSLog(@"%p",[[[FTManager alloc] init] copy]);
2022-04-19 14:14:41.308590+0800 ForTest[3773:68879] 0x6000014faa30
2022-04-19 14:14:41.308763+0800 ForTest[3773:68879] 0x6000014faa30
2022-04-19 14:14:41.308916+0800 ForTest[3773:68879] 0x6000014faa30

weak

1.weak的作用
weak 關(guān)鍵字的作用弱引用谤辜，所引用對(duì)象的計(jì)數(shù)器不會(huì)加一，并在引用對(duì)象被釋放的時(shí)候自動(dòng)被設(shè)置為 nil价捧。
2.weak的實(shí)現(xiàn)原理
第一丑念、通過(guò)weak編譯解析，可以看出來(lái)weak通過(guò)runtime初始化的并維護(hù)的结蟋；
第二脯倚、weak和strong都是Object-C的修飾詞，而strong是通過(guò)runtime維護(hù)的一個(gè)自動(dòng)計(jì)數(shù)表結(jié)構(gòu)椎眯。
綜上：weak是有Runtime維護(hù)的weak表挠将。
3.weak釋放為nil過(guò)程
weak被釋放為nil胳岂，需要對(duì)對(duì)象整個(gè)釋放過(guò)程了解编整，如下是對(duì)象釋放的整體流程：
1舔稀、調(diào)用objc_release
2、因?yàn)閷?duì)象的引用計(jì)數(shù)為0掌测，所以執(zhí)行dealloc
3内贮、在dealloc中，調(diào)用了_objc_rootDealloc函數(shù)
4汞斧、在_objc_rootDealloc中夜郁，調(diào)用了object_dispose函數(shù)
5、調(diào)用objc_destructInstance
6粘勒、最后調(diào)用objc_clear_deallocating竞端。

http://www.reibang.com/p/f331bd5ce8f8

信號(hào)量

在IOS系統(tǒng)GCD的semaphore.h頭文件中提供三個(gè)方法進(jìn)行PV操作
// 這value是初始化多少個(gè)信號(hào)量
1.dispatch_semaphore_create(long value); 
// 這個(gè)方法是P操作對(duì)信號(hào)量減一，dsema這個(gè)參數(shù)表示對(duì)哪個(gè)信號(hào)量進(jìn)行減一庙睡，如果該信號(hào)量為0則等待事富，timeout這個(gè)參數(shù)則是傳入等待的時(shí)長(zhǎng)。
2.dispatch_semaphore_wait(dispatch_semaphore_t dsema, dispatch_time_t timeout); 
// 這個(gè)方法是V操作對(duì)信號(hào)量加一乘陪，dsema這個(gè)參數(shù)表示對(duì)哪個(gè)信號(hào)量進(jìn)行加一
3.dispatch_semaphore_signal(dispatch_semaphore_t dsema);

@interface FTTestViewController ()
/// iphone的數(shù)量
@property (nonatomic,assign) int iphoneNumber;
/// 互斥用的信號(hào)量
@property (nonatomic,strong) dispatch_semaphore_t semaphore;
@end

@implementation FTTestViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    [self test];
 }
- (void)test {
    self.iphoneNumber = 10;
        // 初始化1個(gè)信號(hào)量
        self.semaphore = dispatch_semaphore_create(1);
        
        /// 通過(guò)信號(hào)量進(jìn)行互斥统台，開(kāi)啟三個(gè)窗口(線程)同時(shí)賣(mài)iphone
    NSThread *thread1 = [[NSThread alloc] initWithTarget:self selector:@selector(sellIphone) object:nil];
        thread1.name = @"窗口1";
    NSThread *thread2 = [[NSThread alloc] initWithTarget:self selector:@selector(sellIphone) object:nil];
        thread2.name = @"窗口2";
    NSThread *thread3 = [[NSThread alloc] initWithTarget:self selector:@selector(sellIphone) object:nil];
        thread3.name = @"窗口3";
        [thread1 start];
        [thread2 start];
        [thread3 start];
}
// 通過(guò)信號(hào)量達(dá)到互斥
- (void)sellIphone
{
    while (1) {
        // P操作對(duì)信號(hào)量進(jìn)行減一，然后信號(hào)量變0啡邑，限制其他窗口(線程)進(jìn)入
        dispatch_semaphore_wait(self.semaphore, DISPATCH_TIME_FOREVER);
        
        if (self.iphoneNumber > 0) // 檢查還有沒(méi)iphone可賣(mài)
        {
            NSLog(@"賣(mài)出iphone剩下%d臺(tái)iphone---fromThread:%@",--self.iphoneNumber,[NSThread currentThread]);
            
        }
        else
        {
            NSLog(@"iphone沒(méi)有庫(kù)存了");
            return;
        }
        
        // V操作對(duì)信號(hào)量進(jìn)行加一贱勃，然后信號(hào)量為1，其他窗口(線程)就能進(jìn)入了
        dispatch_semaphore_signal(self.semaphore);
    }
}
2022-04-20 14:15:38.484988+0800 ForTest[19430:548682] 賣(mài)出iphone剩下9臺(tái)iphone---fromThread:<NSThread: 0x600001cbbd80>{number = 9, name = 窗口3}
2022-04-20 14:15:38.485890+0800 ForTest[19430:548680] 賣(mài)出iphone剩下8臺(tái)iphone---fromThread:<NSThread: 0x600001cbbd00>{number = 7, name = 窗口1}
2022-04-20 14:15:38.487929+0800 ForTest[19430:548681] 賣(mài)出iphone剩下7臺(tái)iphone---fromThread:<NSThread: 0x600001cbbd40>{number = 8, name = 窗口2}
2022-04-20 14:15:38.489221+0800 ForTest[19430:548682] 賣(mài)出iphone剩下6臺(tái)iphone---fromThread:<NSThread: 0x600001cbbd80>{number = 9, name = 窗口3}
2022-04-20 14:15:38.490322+0800 ForTest[19430:548680] 賣(mài)出iphone剩下5臺(tái)iphone---fromThread:<NSThread: 0x600001cbbd00>{number = 7, name = 窗口1}
2022-04-20 14:15:38.491334+0800 ForTest[19430:548681] 賣(mài)出iphone剩下4臺(tái)iphone---fromThread:<NSThread: 0x600001cbbd40>{number = 8, name = 窗口2}
2022-04-20 14:15:38.492223+0800 ForTest[19430:548682] 賣(mài)出iphone剩下3臺(tái)iphone---fromThread:<NSThread: 0x600001cbbd80>{number = 9, name = 窗口3}
2022-04-20 14:15:38.492808+0800 ForTest[19430:548680] 賣(mài)出iphone剩下2臺(tái)iphone---fromThread:<NSThread: 0x600001cbbd00>{number = 7, name = 窗口1}
2022-04-20 14:15:38.493185+0800 ForTest[19430:548681] 賣(mài)出iphone剩下1臺(tái)iphone---fromThread:<NSThread: 0x600001cbbd40>{number = 8, name = 窗口2}
2022-04-20 14:15:38.498118+0800 ForTest[19430:548682] 賣(mài)出iphone剩下0臺(tái)iphone---fromThread:<NSThread: 0x600001cbbd80>{number = 9, name = 窗口3}
2022-04-20 14:15:38.499101+0800 ForTest[19430:548680] iphone沒(méi)有庫(kù)存了

/// 通過(guò)同步鎖進(jìn)行互斥谤逼，通過(guò)同步鎖會(huì)比通過(guò)信號(hào)量控制的方式多進(jìn)入該臨界代碼（線程數(shù)量-1）次
- (void)sellIphoneWithSynchronization
{
    while (1) {
        
        @synchronized (self) {
            if (self.iphoneNumber > 0) // 檢查還有沒(méi)iphone可賣(mài)
            {
                NSLog(@"%@賣(mài)出iphone剩下%d臺(tái)iphone",[NSThread currentThread].name,--self.iphoneNumber);
            }
            else
            {
                NSLog(@"iphone沒(méi)有庫(kù)存了");
                return;
            }
 
        }
    }
}

@end

link https://blog.csdn.net/fanyun_01/article/details/111878096

隊(duì)列 隊(duì)列組 柵欄函數(shù) 線程死鎖

隊(duì)列

 /* ##### 隊(duì)列任務(wù) */
   // 一: 同步串行隊(duì)列
   // 參數(shù)1 隊(duì)列名字 參數(shù)2 串行隊(duì)列宏
   dispatch_queue_t queue1 = dispatch_queue_create("myQueue", DISPATCH_QUEUE_SERIAL);
    for(NSInteger i = 0; i < 10; i++){
        // 同步任務(wù) 添加到串行隊(duì)列
        dispatch_sync(queue1, ^{
            NSLog(@"thread == %@ i====%ld",[NSThread currentThread],(long)i);
            // thread == <_NSMainThread: 0x6000002c0000>{number = 1, name = main} i====8
            // thread == <_NSMainThread: 0x6000002c0000>{number = 1, name = main} i====9
        });
    }
    // ps: 主線程 同步串行執(zhí)行任務(wù)

    // 二: 同步并行隊(duì)列
    dispatch_queue_t queue2 = dispatch_queue_create("myQueue", DISPATCH_QUEUE_CONCURRENT);
    for(NSInteger i = 0; i < 10; i++){
        dispatch_sync(queue2, ^{
            NSLog(@"thread == %@ i====%ld",[NSThread currentThread],(long)i);
        });
    }
    // ps: 主線程 同步執(zhí)行任務(wù)

    //三: 異步串行隊(duì)列
    dispatch_queue_t queue3 = dispatch_queue_create("myQueue", DISPATCH_QUEUE_SERIAL);
        for(NSInteger i = 0; i < 10; i++){
            dispatch_async(queue3, ^{
                NSLog(@"thread == %@ i====%ld",[NSThread currentThread],(long)i);
            });
    }
    // ps: 開(kāi)辟一條子線程 串行執(zhí)行任務(wù)

    //四: 異步并行隊(duì)列
    dispatch_queue_t queue4 = dispatch_queue_create("myQueue", DISPATCH_QUEUE_CONCURRENT);
        for(NSInteger i = 0; i < 10; i++){
            dispatch_async(queue4, ^{
                NSLog(@"thread == %@ i====%ld",[NSThread currentThread],(long)i);
            });
//            thread == <NSThread: 0x600001104700>{number = 4,  name = (null)} i====7
//            thread == <NSThread: 0x6000024cb900>{number = 11, name = (null)} i====8
//            thread == <NSThread: 0x6000024f5340>{number = 5,  name = (null)} i====9
    }
    // ps: 開(kāi)辟多條子線程 并行執(zhí)行任務(wù)

    // 開(kāi)辟線程主要看 dispatch_async 異步

    //五: 異步 主隊(duì)列
    dispatch_queue_t queue5 = dispatch_get_main_queue();
       for(NSInteger i = 0; i < 10; i++){
           sleep(2);
           dispatch_async(queue5, ^{
               NSLog(@"thread == %@ i====%ld",[NSThread currentThread],(long)i);
           });
    }
    // ps: 主線程 串行執(zhí)行任務(wù)

隊(duì)列組

//    六: 隊(duì)列組
    dispatch_group_t group = dispatch_group_create();
    dispatch_queue_t concurrentQueue = dispatch_queue_create("concurrentQueue", DISPATCH_QUEUE_CONCURRENT);

        dispatch_group_async(group, concurrentQueue, ^{
            for (int i = 0; i < 3; i++)
            {
                NSLog(@"Task1 %@ %d", [NSThread currentThread], i);
            }
        });
        dispatch_group_async(group, dispatch_get_main_queue(), ^{
            for (int i = 0; i < 3; i++)
            {
                NSLog(@"Task2 %@ %d", [NSThread currentThread], i);
            }
        });
        dispatch_group_async(group, concurrentQueue, ^{
            for (int i = 0; i < 3; i++)
            {
                NSLog(@"Task3 %@ %d", [NSThread currentThread], i);
            } //
        });
        dispatch_group_notify(group, concurrentQueue, ^{
            NSLog(@"All Task Complete");
    });
    
     Task3 <NSThread: 0x600000bcf400>{number = 5, name = (null)} 0
     Task1 <NSThread: 0x600000b8a740>{number = 8, name = (null)} 0
     Task3 <NSThread: 0x600000bcf400>{number = 5, name = (null)} 1
     Task1 <NSThread: 0x600000b8a740>{number = 8, name = (null)} 1
     Task3 <NSThread: 0x600000bcf400>{number = 5, name = (null)} 2
     Task1 <NSThread: 0x600000b8a740>{number = 8, name = (null)} 2
     Task2 <_NSMainThread: 0x600000be8980>{number = 1, name = main} 0
     Task2 <_NSMainThread: 0x600000be8980>{number = 1, name = main} 1
     Task2 <_NSMainThread: 0x600000be8980>{number = 1, name = main} 2
     All Task Complete
    
      // ps 異步并行隊(duì)列 正常會(huì)開(kāi)啟n調(diào)線程 這里只開(kāi)啟了一條線程???

柵欄函數(shù)
柵欄函數(shù)的作?：
1 實(shí)現(xiàn)多讀單寫(xiě), 當(dāng)鎖用
2 控制線程執(zhí)行順序, 達(dá)到同步的效果
柵欄函數(shù)注意:
1 柵欄函數(shù)只能控制同一并發(fā)隊(duì)列
2 柵欄函數(shù)要想起作用贵扰，那么創(chuàng)建任務(wù)隊(duì)列就必須使用dispatch_queue_create()該種方式，使用全局隊(duì)列柵欄函數(shù)無(wú)法發(fā)揮作用流部；
dispatch_barrier_async：前面的任務(wù)執(zhí)行完畢戚绕，才會(huì)來(lái)到這里
dispatch_barrier_sync：作用相同，但是這個(gè)會(huì)堵塞線程贵涵，影響后面的執(zhí)行

@interface FTTestViewController ()
{
    // 定義一個(gè)并發(fā)隊(duì)列
    dispatch_queue_t _concurrent_queue;
    
    // 用戶(hù)數(shù)據(jù)中心, 可能多個(gè)線程需要數(shù)據(jù)訪問(wèn)
    NSMutableDictionary *_userCenterDic;
}

- (void)viewDidLoad {
    [super viewDidLoad];
   //七: 柵欄函數(shù)
    // 多讀單寫(xiě)
    // 通過(guò)宏定義 DISPATCH_QUEUE_CONCURRENT 創(chuàng)建一個(gè)并發(fā)隊(duì)列
      _concurrent_queue = dispatch_queue_create("read_write_queue", DISPATCH_QUEUE_CONCURRENT);
      // 創(chuàng)建數(shù)據(jù)容器
      _userCenterDic = [NSMutableDictionary dictionary];

    [self barrierTest]; // 柵欄函數(shù)測(cè)試
}

- (id)objectForKey:(NSString *)key
{
    __block id obj;
    // 同步讀取指定數(shù)據(jù),立刻返回讀取結(jié)果
    dispatch_sync(_concurrent_queue, ^{
        obj = [self->_userCenterDic objectForKey:key];
    });
    
    return obj;
}

- (void)setObject:(id)obj forKey:(NSString *)key
{
    // 異步柵欄調(diào)用設(shè)置數(shù)據(jù)
    dispatch_barrier_async(_concurrent_queue, ^{
        [self->_userCenterDic setObject:obj forKey:key];
    });
}

// 柵欄函數(shù)測(cè)試 舉例
- (void)barrierTest {    
    // 建立全局并發(fā)隊(duì)列
dispatch_queue_t concurrentQueue = dispatch_queue_create("concurrentQueue", DISPATCH_QUEUE_CONCURRENT);
    dispatch_async(concurrentQueue, ^{
        NSLog(@"任務(wù)(一)%@",[NSThread currentThread]);
    });
    dispatch_async(concurrentQueue, ^{
        NSLog(@"任務(wù)(二)%@",[NSThread currentThread]);
    });
    dispatch_async(concurrentQueue, ^{
        NSLog(@"任務(wù)(三)%@",[NSThread currentThread]);
    });
    dispatch_barrier_async(concurrentQueue, ^{
        NSLog(@"(柵欄函數(shù))%@",[NSThread currentThread]);
    });
    dispatch_async(concurrentQueue, ^{
        NSLog(@"任務(wù)(四)%@",[NSThread currentThread]);
    });
    NSLog(@"開(kāi)始工作");
}
2022-04-20 19:11:49.205886+0800 ForTest[26101:755643] 開(kāi)始工作
2022-04-20 19:11:49.206003+0800 ForTest[26101:755903] 任務(wù)(二)<NSThread: 0x600002ceb140>{number = 4, name = (null)}
2022-04-20 19:11:49.206010+0800 ForTest[26101:755908] 任務(wù)(一)<NSThread: 0x600002c9a1c0>{number = 6, name = (null)}
2022-04-20 19:11:49.206041+0800 ForTest[26101:755901] 任務(wù)(三)<NSThread: 0x600002c89c00>{number = 3, name = (null)}
2022-04-20 19:11:49.206232+0800 ForTest[26101:755908] (柵欄函數(shù))<NSThread: 0x600002c9a1c0>{number = 6, name = (null)}
2022-04-20 19:11:49.206398+0800 ForTest[26101:755901] 任務(wù)(四)<NSThread: 0x600002c89c00>{number = 3, name = (null)}

線程死鎖
觸發(fā)場(chǎng)景: 主線程/同步 串行隊(duì)列/同步 死鎖

dispatch_queue_t queue = dispatch_get_main_queue();
        dispatch_sync(queue, ^{
            NSLog(@"執(zhí)行任務(wù)2");  // Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
    });// 往主線程里面 同步添加任務(wù) 會(huì)發(fā)生死鎖現(xiàn)象

    dispatch_queue_t myQueue = dispatch_queue_create("myQueue", DISPATCH_QUEUE_SERIAL);
        dispatch_async(myQueue, ^{ // 異步串行隊(duì)列
            NSLog(@"1111,thread====%@",[NSThread currentThread]);

        dispatch_sync(myQueue, ^{ // 同步串行隊(duì)列
            NSLog(@"2222,thread====%@",[NSThread currentThread]);
//            Thread 4: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)  crash
        });
    });