OSSpinLock
自旋鎖(過期了)，等待鎖的線程會處于忙等（busy-wait）狀態(tài)，一直占用著CPU資源
目前應(yīng)不再安全，可能出現(xiàn)優(yōu)先級反轉(zhuǎn)問題
優(yōu)先級低的線程1先進(jìn)入，鎖住句惯。CPU把大量時(shí)間給優(yōu)先級高的線程2土辩，優(yōu)先級高的線程2等線程1解鎖，優(yōu)先級低的線程獲得不到CPU的時(shí)間宗弯，無法解鎖脯燃。出現(xiàn)了假死鎖。
#import <libkern/OSAtomic.h>
OSSpinLock lock = OS_SPINLOCK_INIT; // 需要全局初始化一次
// 鎖
OSSpinLockLock(&lock);
// 解鎖
OSSpinLockUnLock(&lock);

// 嘗試加鎖 
if (OSSpinLockTry(&lock)) {
    OSSpinLockUnLock(&lock);
}

os_unfair_lock
iOS10以后
優(yōu)化了OSSpinLock蒙保，等待os_unfair_lock鎖的線程
#import <os/lock.h>
typedef struct os_unfair_lock_s {
uint32_t _os_unfair_lock_opaque;
} os_unfair_lock, *os_unfair_lock_t;

@property(assign, nonatomic) os_Unfair_lock lock;

os_unfair_lock_lock(&lock);
os_unfair_lock_trylock(&lock);
os_unfair_lock_unlock(&lock);

pthread_mutex
pthread開頭都是跨平臺的
mutex:互斥
互斥鎖辕棚，等待鎖的線程會處于休眠狀態(tài)
#import <pthread.h>
// pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
// 初始化屬性
pthread_mutexattr_t attr;
pthread_mutextattr_init(&attr);
// PTHREAD_MUTEX_DEFAULT 默認(rèn)鎖
// 檢測錯(cuò)誤鎖
// PTHREAD_MUTEX_RECURSIVE 遞歸鎖
允許同一個(gè)線程對一把鎖進(jìn)行重復(fù)加鎖
允許同一個(gè)線程先多次加鎖，然后再解鎖邓厕，加鎖多少次逝嚎，解鎖多少次。
a線程鎖了详恼，b線程來了要等待
pthread_mutextattr_settype(&attr, PTHREAD_MUTEX_DEFAULT);
// 初始化鎖
pthread_mutex_init(&mutex, &attr);
// 銷毀屬性
pthread_mutexattr_destroy(&attr);

pthread_mutex_lock(&mutex);
pthread_mutex_unlock(&mutex);

// 銷毀鎖 （dealloc）
phread_mutex_destroy(&mutex);

- (void)test {
    pthread_mutex_lock(&mutex);    
    NSLog(@“—0”);
    [self test1];

    pthread_mutex_unlock(&mutex);
}
- (void)test1 {
    pthread_mutex_lock(&mutex);    

    NSLog(@“—1”);

    pthread_mutex_unlock(&mutex);
}
死鎖补君，解決辦法：兩把鎖，test1里再用一把鎖mutex2即可

- (void)test {
    pthread_mutex_lock(&mutex);    
    // 遞歸 使用PTHREAD_MUTEX_RECURSIVE
    static int count = 0;
    if (count < 5) {
        count++;
        [self test];
    }

    pthread_mutex_unlock(&mutex);
}
允許先多次加鎖昧互，然后再解鎖挽铁，加鎖多少次，解鎖多少次敞掘。

// 條件叽掘。
@property(assign, nonatomic)pthread_cond_t cond;

// 初始化
 pthread_cond_init(&cond, NULL);

// 兩條線程 先執(zhí)行remove方法
[[[NSTread alloc] initWithTarget:self selector:@selector(remove) objcet: nil] start];
[[[NSTread alloc] initWithTarget:self selector:@selector(add) objcet: nil] start];

- (void)remove {
    pthread_mutex_lock(&mutex);
    if (self.data.count == 0) {
        // 等待繼續(xù)執(zhí)行的條件cond 把mutex鎖放開
        // 收到可以繼續(xù)執(zhí)行的條件 mutex加鎖
        pthread_cond_wait(&cond, &mutex);
    }
    
    [self.data removeLastObject];
    NSLog(@“刪除了元素”);
    
    pthread_mutex_unlock(&mutex);
}

- (void)add {
    pthread_mutex_lock(&mutex);
    sleep(1);

    [self.data addObject:@“te”];
    NSLog(@“添加了元素”);
    
    // 通知等待的cond 可以繼續(xù)執(zhí)行了
    pthread_cond_signal(&cond)
    
    pthread_mutex_unlock(&mutex);
}

NSLock
對pthread_mutex普通鎖的封裝

遵守NSLocking兩個(gè)協(xié)議
    lock和unlock兩個(gè)方法

-(BOOL)tryLock; // 嘗試加鎖
-(BOOL)lockBeforeDate: (NSDate *)limit; // 相比tryLock有個(gè)等待的時(shí)間 會阻塞
    在這個(gè)時(shí)間之前，能等到鎖玖雁，就給這個(gè)鎖加鎖 加鎖成功 繼續(xù)往下走
    在時(shí)間內(nèi)更扁，沒等到鎖，加鎖失敗赫冬，代碼繼續(xù)往前走
@property(strong, nonatomic) NSLock *lock;
self.lock = [[NSLock allock] init];

[self.lock lock];
[self.lock unlock];

NSRecursiveLock <NSLocking>
對pthread_mutex遞歸鎖鎖的封裝
NSRecursiveLock方法同NSLock

NSCondition<NSLocking>
對pthread_cond_t的封裝有l(wèi)ock和unlock方法
-(void)wait;
-(BOOL)waitUntilDate:(NSDate *)limit;
-(void)signal;
-(void)broadcast;

NSConditionLock<NSLocking>
條件鎖
內(nèi)部存儲的條件之是1（初始化是多少）時(shí)候才能加鎖
對pthread_cond_t和pthread_mutex_t的封裝

@property(strong, nonatomic) NSConditionLock *conditionLock;

self.conditionLock = [[NSConditonLock allok] initWithCondition:1];

- (void)one {
    [self.conditionLock lockWhenCondition: 1];// 條件之為1才能加鎖
    NSLog(@“11”);
    [self.conditionLock lockWhenCondition: 2];// 設(shè)置內(nèi)部條件值為2 并解鎖
}

- (void)two {
    [self.conditionLock lockWhenCondition: 3];// 條件之為2才能加鎖
    NSLog(@“22”);
    [self.conditionLock unlock];    
}
- (void)three {
    [self.conditionLock lockWhenCondition: 3];// 條件之為2才能加鎖
    NSLog(@“22”);
    [self.conditionLock unlock];    
}
效果：一定先執(zhí)行one 再執(zhí)行two 最后執(zhí)行three

dispatch_semaphore
信號量信號量的初始值浓镜，可以用來控制線程并發(fā)訪問的最大數(shù)量
最大并發(fā)量
線程同步信號量設(shè)置為1 DISPATCH_TIME_FOREVER 即可保證只有一條線程執(zhí)行
@property (strong, nonatomic) dispatch_semaphore_t semaphore;

self.semaphore = dispatch_semaphore_create(5); // 最大并發(fā)5

- (void)test {
    for (i = 0; i< 20; i++) {
        [[[NSThread alloc] initWithTarget: self selector@selector(run) object:nil] start];
    }
}

- (void)run {
    // 信號量的值 > 0，就讓信號量的值減1劲厌，然后繼續(xù)執(zhí)行代碼
    // 信號量的值 <= 0 就會休眠等待 具體等多久 看dispatch_semaphore_wait第二個(gè)參數(shù)
    dispatch_semaphore_wait(self.semaphore, DISPATCH_TIME_FOREVER);
    
    sleep(2);
    NSLog(@“%@“, [NSTread crrentThread]);
    
    // 剛執(zhí)行到這里 信號量為0 
    // 信號量+1
    dispatch_semaphore_signal(self.semaphore);
}

// 每個(gè)方法都是獨(dú)立一把鎖
-(void)test {
    static dispatch_semaphore_t semaphore;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^ {
        semaphore = dispatch_semaphore_create(1);
    })

    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);

    // 要加鎖的代碼        

    dispatch_semahore_signal(semaphore);
}

// 宏
#define SemaphoreBegin \
static dispatch_semaphore_t semaphore; \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^ { \
    semaphore = dispatch_semaphore_create(1); \
})\ 
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);

#define SemaphoreEnd \
    dispatch_semahore_signal(semaphore);

-(void)test {
    SemaphoreBegin;

    // 要加鎖的代碼        

    SemaphoreEnd;
}

dispatch_queue(DISPATCH_QUEUE_SERIAL)
串行隊(duì)列
@property(strong, nonatomic)dispatch_queue_t queue;

self.queue = dispatch_queue_create(“q”, DISPATCH_QUEUE_SERIAL);

- (void)saleTicket {
    dispatch_sync({self.queue, ^{
        NSLog(@“sale“);
    });
}

@synchronized
對prhead_mutex遞歸鎖的封裝
不推薦使用
{
@synchronized(self) {
[self run];
}
}

讀寫安全
1膛薛、dispatch_semaphore_t 信號量
讀和寫都給鎖住了讀沒必要鎖住
2、

import <pthread.h>

@property (assign, nonatomic)pthread_rwlock lock;

{

pthread_rwlock_init(&lock, NULL)    

[[[NSTread alloc] initWithTarget:self selector:@selector(read) objcet: nil] start];
[[[NSTread alloc] initWithTarget:self selector:@selector(write) objcet: nil] start];

}

-(void)read {
pthread_rwlock_rdlock(&lock);
NSLog(@“du”);
pthread_rwlock_unlock(&lock);
}

-(void)write {
pthread_rwlock_wrlock(&lock);
NSLog(@“xie”);
pthread_rwlock_unlock(&lock);
}

-(void)dealloc {
pthread_rwlock_dispose(&lock);
}

-(void)read {
dispatch_async(q, ^{
NSLog(@“du”);
})
}

-(void)write {
dispatch_barrier_async(q, ^ {
NSLog(@“xie”);
})
}

iOS - 鎖

iOS - 鎖

import <pthread.h>