线程中什么情况下会造成死锁

线程中什么情况下会造成死锁

什么是死锁？
死锁：假如你有两把锁a、b，当线程1拿到锁a的时候又想去拿锁b，线程2拿到了锁b又想去拿锁a，这时候两个线程竞争谁也拿不到锁，导致线程无法运行下去，造成了死锁。

代码验证如下

#include<stdio.h>
#include<pthread.h>
//int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
  //                        void *(*start_routine) (void *), void *arg)
int data=0;

pthread_mutex_t mutex;
pthread_mutex_t mutex2;

void *fun1(void *arg)
{

        pthread_mutex_lock(&mutex);
        sleep(1);
        pthread_mutex_lock(&mutex2);
        while(1)
        {
                data++;
                printf("t1 data=%d\n",data);
                if(data==3)
                {
                        pthread_mutex_unlock(&mutex);
                        pthread_exit(NULL);
                }
                sleep(1);
        }
}

void *fun2(void *arg)
{

        while(1)
        {
                pthread_mutex_lock(&mutex2);
                sleep(1);
                pthread_mutex_lock(&mutex);
                data++;
                pthread_mutex_unlock(&mutex2);
                sleep(1);
                printf("t2 data=%d\n",data);

        }
}
int main()
{
        pthread_t t1;
        pthread_t t2;
        int ret;
        int t=100;

        pthread_mutex_init(&mutex,NULL);
        pthread_mutex_init(&mutex2,NULL);
        ret=pthread_create(&t1,NULL,fun1,(void *)&t);
        if(ret==0)
        {
                printf("main:create success\n");
        }

        ret=pthread_create(&t2,NULL,fun2,(void *)&t);
        if(ret==0)
        {
                printf("main:create success\n");
        }
        printf("main:%ld\n",(unsigned long)pthread_self());


        pthread_join(t1,NULL);
        pthread_join(t2,NULL);

        pthread_mutex_destroy(&mutex);
        pthread_mutex_destroy(&mutex2);
        return 0;
}