CS202: HW 2: Linked list, shell, concurrency

These problems should be done on your own. We're not going to be grading them strictly (we'll mainly look at whether you attempted them). But they will be reinforcing knowledge and skills, so you should work through them carefully.

Linked lists

This question will provide some practice with linked lists (you may thank us during job interview season: linked lists are common subjects of interview questions).

In the code below, we specify a data structure node_t:

    struct node_t {
        int id;
        char name[10];
        struct node_t *next;
    };

A linked list consists of a list of these structures, connected via the next field, which is a pointer to another node_t. Given the head of a linked list (a pointer to the first element), the program can traverse the linked list by following the next pointers (you will do that in the exercise below). The last element in a linked list (assuming the list has been set up correctly) has its next field set to NULL.

We wish to write code that stores a list of students, each with an id and a name. We also will arrange to keep all elements keep sorted by student ids. The skeleton is below. You will fill it in.

    /* Iterate through the sorted list (by node_t::id), and find the position after
     * which the new 'node' should be inserted in the list. Ensure that the list
     * is kept sorted. Return the element just before the newly inserted one.
     * If the new 'node' should be inserted at the beginning, return NULL.
     */
    node_t *
    find_insert_pos(node_t *head, node_t *node)
    {
        if (head == NULL) return NULL;

        node_t *ret = NULL;

        // 2.1 your code here

        return ret;
    }

    /* insert a new 'node' into the list 'head', return the new head of the list.
    node_t *
    insert(node_t *head, node_t *node)
    {
        if (head == NULL) return node;

        // find the proper position to insert this node pair.
        node_t *pos = find_insert_pos(head, node);

        // 2.2 your code here

        return head;
    }

    int
    main(void)
    {
        node_t *student_list = NULL;

        // init first student Alice
        node_t *student_1 = (node_t *)malloc(sizeof(node_t));
        student_1->id = 1002;
        strcpy(student_1->name, "Alice");
        student_1->next = NULL;

        // init second student Bob
        node_t *student_2 = (node_t *)malloc(sizeof(node_t));
        student_2->id = 1000;
        strcpy(student_2->name, "Bob");
        student_2->next = NULL;

        student_list = insert(student_list, student_1);
        student_list = insert(student_list, student_2);

        // now we should have a student list:
        //    <1000, Bob> -> <1002, Alice> -> NULL

        ... free resources ...

        return 0;
    }

Shell

There is a file 'members.txt'. Assume it is in the following form:

        Name:John
        NetId:j22
        email:john@nyu.edu
        Name:Amy
        NetId:a123
        email:amy@nyu.edu
        ...

Processes and threads

Concurrency

Based on the following code:

    int i = 0; 

    void
    foo(void *)
    {
        int n = i;
        i = i + 1;
        printf("foo: %d\n", n);
    }

    void
    boo(void *)
    {
        int n = i;
        i = i + 1;
        printf("boo: %d\n", n);
    }

    int
    main(void)
    {
        tid_foo = create_thread(foo); 
        tid_boo = create_thread(boo);

        // wait for threads to finish
        join_thread(tid_foo);
        join_thread(tid_boo);

        printf("main: %d\n", i);
        return 0;
    }

Handing in the homework

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