C语言多线程开发中死锁与读写锁问题详解

//多线程多锁，抢占锁资源
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
// 创建2个互斥量
pthread_mutex_t mutex1, mutex2;
void * workA(void * arg) {
    pthread_mutex_lock(&mutex1);
    sleep(1);
    pthread_mutex_lock(&mutex2);
    printf("workA....\n");
    pthread_mutex_unlock(&mutex2);
    pthread_mutex_unlock(&mutex1);
    return NULL;
}
void * workB(void * arg) {
    pthread_mutex_lock(&mutex2);
    sleep(1);
    pthread_mutex_lock(&mutex1);
    printf("workB....\n");
    pthread_mutex_unlock(&mutex1);
    pthread_mutex_unlock(&mutex2);
    return NULL;
}
int main() {
    // 初始化互斥量
    pthread_mutex_init(&mutex1, NULL);
    pthread_mutex_init(&mutex2, NULL);
    // 创建2个子线程
    pthread_t tid1, tid2;
    pthread_create(&tid1, NULL, workA, NULL);
    pthread_create(&tid2, NULL, workB, NULL);
    // 回收子线程资源
    pthread_join(tid1, NULL);
    pthread_join(tid2, NULL);
    // 释放互斥量资源
    pthread_mutex_destroy(&mutex1);
    pthread_mutex_destroy(&mutex2);
    return 0;
}

/*
    读写锁的类型 pthread_rwlock_t
    int pthread_rwlock_init(pthread_rwlock_t *restrict rwlock, const pthread_rwlockattr_t *restrict attr);
    int pthread_rwlock_destroy(pthread_rwlock_t *rwlock);
    int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);
    int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock);
    int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);
    int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock);
    int pthread_rwlock_unlock(pthread_rwlock_t *rwlock);
    案例：8个线程操作同一个全局变量。
    3个线程不定时写这个全局变量，5个线程不定时的读这个全局变量
*/
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
// 创建一个共享数据
int num = 1;
// pthread_mutex_t mutex;
pthread_rwlock_t rwlock;
void * writeNum(void * arg) {
    while(1) {
        pthread_rwlock_wrlock(&rwlock);
        num++;
        printf("++write, tid : %ld, num : %d\n", pthread_self(), num);
        pthread_rwlock_unlock(&rwlock);
        usleep(100);
    }
    return NULL;
}
void * readNum(void * arg) {
    while(1) {
        pthread_rwlock_rdlock(&rwlock); 
        printf("===read, tid : %ld, num : %d\n", pthread_self(), num);
        pthread_rwlock_unlock(&rwlock);
        usleep(100);
    }
    return NULL;
}
int main() {
   pthread_rwlock_init(&rwlock, NULL);
    // 创建3个写线程，5个读线程
    pthread_t wtids[3], rtids[5];
    for(int i = 0; i < 3; i++) {
        pthread_create(&wtids[i], NULL, writeNum, NULL);
    }
    for(int i = 0; i < 5; i++) {
        pthread_create(&rtids[i], NULL, readNum, NULL);
    }
    // 设置线程分离
    for(int i = 0; i < 3; i++) {
       pthread_detach(wtids[i]);
    }
    for(int i = 0; i < 5; i++) {
         pthread_detach(rtids[i]);
    }
    pthread_exit(NULL);
    pthread_rwlock_destroy(&rwlock);
    return 0;
}