Deadlock

• Book1 and Book2 are needed to do assignment, Bob and Allen all need to borrow these two books.
• Allen borrows Book1 first, after he borrowed Book1, he starts to find Book2.

• Bob borrows Book2 first, anfter he borrowed Book2, he starts to find Book1.

• No one can borrow these two books.

#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>


void *Allen(void *arg);
void *Bob(void *arg);

pthread_mutex_t book1=PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t book2=PTHREAD_MUTEX_INITIALIZER;

int main() {
    pthread_t tid1, tid2;
    pthread_create(&tid1, NULL, Allen, NULL);
    pthread_create(&tid2, NULL, Bob, NULL);

    pthread_join(tid1, NULL);
    pthread_join(tid2, NULL);

    return 0;
}

void *Allen(void *arg) {
    pthread_mutex_lock(&book1);
    sleep(10);
    pthread_mutex_lock(&book2);
    printf("Allen has collected all books he need, he is going to do homework!");
    pthread_mutex_unlock(&book2);
    pthread_mutex_unlock(&book1);
}

void *Bob(void *arg) {
    pthread_mutex_lock(&book2);
    sleep(10);
    pthread_mutex_lock(&book1);
    printf("Bob has collected all books he need, he is going to do homework!");
    pthread_mutex_unlock(&book1);
    pthread_mutex_unlock(&book2);
}

How can you solve this problem? You can find many ways to solve this deadlock problem: timeout, require for resources in a sequence, changing priority level time to time......