pthread_mutex_t

首先是苹果的解释：

Detects when a mutex is used before it's initialized.

Overview

This check detects anytime pthread_mutex_lock(_:) or pthread_mutex_unlock(_:) is called with a pthread_mutex_t variable that wasn't initialized. Attempting to use an uninitialized mutex results in an error, and removes any guarantees about ordering that would exist while a mutex is locked.

Use of Uninitialized Mutex in C

In the following example, the pthread_mutex_lock(_:) function is called on an uninitialized pthread_mutex_t variable.

static pthread_mutex_t mutex;
void performWork() {
    pthread_mutex_lock(&mutex); // Error: uninitialized mutex
    // ...
    pthread_mutex_unlock(&mutex);
}

下面是自己的理解和例子代码

#import <Foundation/Foundation.h>
@interface NSLockTest : NSObject
- (void)forTest;
@end

#import "NSLockTest.h"
#include <pthread.h>
@interface NSLockTest()
@property (nonatomic,strong) NSArray *tickets;
@property (nonatomic,assign) int soldCount;

@end
@implementation NSLockTest
pthread_mutex_t pMutex;
- (void)forTest
{
//    pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;
    pthread_mutex_init(&pMutex,NULL);
    self.tickets = @[@"南京-北京A101",@"南京-北京A102",@"南京-北京A103",@"南京-北京A104",@"南京-北京A105",@"南京-北京A106",@"南京-北京A107",@"南京-北京A108",@"南京-北京A109",@"南京-北京A110",@"南京-北京A111",@"南京-北京A112",@"南京-北京A113",@"南京-北京A114",@"南京-北京A115",@"南京-北京A116",@"南京-北京A117",@"南京-北京A118",@"南京-北京A119",@"南京-北京A120",@"南京-北京A121",@"南京-北京A122",@"南京-北京A123",@"南京-北京A124",@"南京-北京A125",@"南京-北京A126",@"南京-北京A127",@"南京-北京A128",@"南京-北京A129",@"南京-北京A130"];
    //第一窗口
    NSThread *windowOne = [[NSThread alloc] initWithTarget:self selector:@selector(soldTicket) object:nil];
    windowOne.name = @"一号窗口";
    [windowOne start];
    //第二窗口
    NSThread *windowTwo = [[NSThread alloc] initWithTarget:self selector:@selector(soldTicket) object:nil];
    windowTwo.name = @"二号窗口";
    [windowTwo start];
    //第三窗口
    NSThread *windowThree = [[NSThread alloc] initWithTarget:self selector:@selector(soldTicket) object:nil];
    windowThree.name = @"三号窗口";
    [windowThree start];
    //第四窗口
    NSThread *windowFour = [[NSThread alloc] initWithTarget:self selector:@selector(soldTicket) object:nil];
    windowFour.name = @"四号窗口";
    [windowFour start];
}
-(void)soldTicket
{
    pthread_mutex_lock(&pMutex);
    if (self.soldCount == self.tickets.count) {
        NSLog(@"=====%@ 剩余票数：%lu",[[NSThread currentThread] name],self.tickets.count-self.soldCount);
        pthread_mutex_unlock(&pMutex);
        return;
    }
    //延时卖票
    [NSThread sleepForTimeInterval:0.2];
    self.soldCount++;
    NSLog(@"=====%@ %@ 剩%lu",[[NSThread currentThread] name],self.tickets[self.soldCount-1],self.tickets.count-self.soldCount);
    pthread_mutex_unlock(&pMutex);
    //一直卖票
    [self soldTicket];
    
}
@end

注意

1、申明一个互斥锁，pthread_mutex_t pMutex;

2、初始化它，pthread_mutex_init(&pMutex,NULL);

3、使用pMutex之前一定要初始化，否则不生效

4、获得锁，pthread_mutex_lock(&pMutex);

5、解锁，pthread_mutex_unlock(&pMutex);