/*
    Idea: order of locking is important

    A robot has 4 arms:
        Arm 1 is made of component A and C
        Arm 2 is made of component C and B
        Arm 3 is made of component C and A
        Arm 4 is made of component B and A
*/

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

pthread_mutex_t component_A_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t component_B_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t component_C_mutex = PTHREAD_MUTEX_INITIALIZER;

// Arm 1 must get component A and component C
void* arm1(void* arg) {
    pthread_mutex_lock(&component_A_mutex);
    printf("Arm 1 acquired Component A\n");

    pthread_mutex_lock(&component_C_mutex);
    printf("Arm 1 acquired Component C\n");

    printf("Arm 1 is assembling\n");

    pthread_mutex_unlock(&component_C_mutex);
    pthread_mutex_unlock(&component_A_mutex);
    return NULL;
}

// Arm 2 must acquire component C and component B
void* arm2(void* arg) {
    pthread_mutex_lock(&component_C_mutex);
    printf("Arm 2 acquired Component C\n");

    pthread_mutex_lock(&component_B_mutex);
    printf("Arm 2 acquired Component B\n");

    printf("Arm 2 is assembling\n");

    pthread_mutex_unlock(&component_C_mutex);
    pthread_mutex_unlock(&component_B_mutex);
    return NULL;
}

// Arm C must acquire component A and component C
void* arm3(void* arg) {
    pthread_mutex_lock(&component_A_mutex);
    printf("Arm 3 acquired Component C\n");

    pthread_mutex_lock(&component_C_mutex);
    printf("Arm 3 acquired Component A\n");

    printf("Arm 3 is assembling\n");

    pthread_mutex_unlock(&component_A_mutex);
    pthread_mutex_unlock(&component_C_mutex);
    return NULL;
}

// arm 4 must acquire component A and component B
void* arm4(void* arg) {
    pthread_mutex_lock(&component_A_mutex);
    printf("Arm 4 acquired Component A\n");

    pthread_mutex_lock(&component_B_mutex);
    printf("Arm 4 acquired Component B\n");


    printf("Arm 4 is assembling\n");

    pthread_mutex_unlock(&component_B_mutex);
    pthread_mutex_unlock(&component_A_mutex);
    return NULL;
}

int main() {
    // Create four threads to assemble each arm
    pthread_t thread_id1;
    pthread_t thread_id2;
    pthread_t thread_id3;
    pthread_t thread_id4;
    pthread_create(&thread_id1, NULL, arm1, NULL);
    pthread_create(&thread_id2, NULL, arm2, NULL);
    pthread_create(&thread_id3, NULL, arm3, NULL);
    pthread_create(&thread_id4, NULL, arm4, NULL);

    // Wait for all four threads to finish
    pthread_join(thread_id1, NULL);
    pthread_join(thread_id2, NULL);
    pthread_join(thread_id3, NULL);
    pthread_join(thread_id4, NULL);

    return 0;
}