一、互斥锁
1. 函数原型
pthread_mutex_init(pthread_mutex_t *restrict mutex, const pthread_mutexattr_t *restrict attr);
pthread_mutex_destroy(pthread_mutex_t *mutex); 分析：
- pthread_mutex_t 类型，其本质是一个结构体，为简化理解，应用时可忽略其实现细节，简单当成整数看待。
- pthread_mutex_t mutex：变量mutex只有两种取值0、1；
函数一参数1：传出参数，调用时应传&mutex
- restrict关键字：只用于限制指针，告诉编译器，所有修改该指针指向内存中内容的操作，只能通过本指针完成。不能通过除本指针以外的其他变量或指针修改。
函数一参数2：互斥属性。是一个传入参数，通常传NULL，选用默认属性(线程间共享).
- 静态初始化：如果互斥锁mutex是静态分配的(定义在全局，或加了static关键字修饰），可以直接使用宏进行初始化。pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
- 动态初始化：局部变量应采用动态初始化, pthread_mutex_init(&mutex, NULL);
2. 函数原型：
pthread_mutex_lock(pthread_mutex_t *mutex);
pthread_mutex_unlock(pthread_mutex_t *mutex); 分析：
- 函数1：没有被上锁，当前线程会将这把锁锁上；被锁上了，当前线程阻塞，锁被打开之后，线程解除阻塞（加锁。可理解为将mutex--（或-1））。
- 函数2：同时将阻塞在该锁上的所有线程全部唤醒解锁(可理解为将mtex++（或+1)).
二、代码清单
1. 测试代码
#include <stdio.h>
#include <string.h>
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>void *tfn(void *arg)
{srand(time(NULL));while(1) {printf("hello ");sleep(rand() % 3); //模拟长时间操作共享资源，导致cpu易主，产生与时间有关的错误printf("word\n");sleep(rand() % 3);}return NULL;
}int main()
{pthread_t tid;srand(time(NULL));pthread_create(&tid, NULL, tfn, NULL);while(1) {printf("HELLO ");sleep(rand() % 3);printf("WORLD\n");sleep(rand() % 3);}return 0;
}输出结果
2. 测试代码
#include <stdio.h>
#include <string.h>
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>void *tfn(void *arg)
{srand(time(NULL));while(1) {printf("hello ");sleep(rand() % 3); //模拟长时间操作共享资源，导致cpu易主，产生与时间有关的错误printf("word\n");sleep(rand() % 3);}return NULL;
}int main()
{pthread_t tid;srand(time(NULL));pthread_create(&tid, NULL, tfn, NULL);while(1) {printf("HELLO ");sleep(rand() % 3);printf("WORLD\n");sleep(rand() % 3);}return 0;
}输出结果
#include<pthread.h>
#include<stdlib.h>
#include<unistd.h>pthread_mutex_t mutex;void* tfn(void* arg)
{srand(time(NULL));while (1) {pthread_mutex_lock(&mutex);printf("hello ");sleep(rand() % 3); //模拟长时间共享资源，导致cpu易主。产生于时间有关的错误 printf("word\n");pthread_mutex_unlock(&mutex);sleep(rand() % 3);}return NULL;
}int main()
{pthread_t tid;srand(time(NULL));pthread_mutex_init(&mutex, NULL);pthread_create(&tid, NULL, tfn, NULL); //mutex == 1while (1) {pthread_mutex_lock(&mutex);printf("HELLO ");sleep(rand() % 3);printf("WORLD\n");pthread_mutex_unlock(&mutex);sleep(rand() % 3);}pthread_mutex_destroy(&mutex);return 0;
}
#include<stdlib.h>
#include<unistd.h>
#include<pthread.h>
#include<errno.h>
#include<stdio.h>pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t *mp;void add(void)
{int i = 10;i = i + 1;i = i + 2;i = i + 3;printf("sum is %d\n", i);
}void thread1(void)
{{pthread_mutex_lock(mp);add();pthread_mutex_unlock(mp);sleep(1);}
}
void thread2(void)
{{pthread_mutex_lock(mp);add();pthread_mutex_unlock(mp);sleep(2);}
}int main(void)
{pthread_t id1, id2;int ret;mp = (pthread_mutex_t*)malloc(sizeof(pthread_mutex_t));pthread_mutex_init(mp, NULL);ret = pthread_create(&id1, NULL, (void*)thread1, NULL);if(ret < 0){perror("pthread_create id1");exit(1);}ret = pthread_create(&id2, NULL, (void*)thread2, NULL);if(ret <0){perror("pthread_create id2");exit(1);}pthread_join(id1, NULL); pthread_join(id2, NULL); pthread_mutex_destroy(mp);free(mp);return 0;
}
