Threads cannot be implemented as a library (reading question)

Please submit your response on Gradescope by Monday, April 17, 2023, 3pm PST.

1. State what the point of section 5.1 is. Then state in what way Figure 3 undercuts the entire point of Section 5.1.

2. We can define the semantics of a volatile variable v as giving two guarantees: (i) no additional loads or stores can be done to v other than what appear in the program text, and (ii) an access to v cannot be reordered with any other volatile access or lock call. Which problems (if any) in Section 4 would this fix?

3. You see the following code below, Eraser said this “double-check lock” idiom is tricky because of memory consistency. Assume the hardware is sequentially consistent and Boehm fixed the compiler to not be stupid about locks (describe your interpretation of what this means). Does this code break? Why or why not?

if (!p) {
    lock();
    if (!p) {
        struct foo *t = foo_new();
        t->bar = bar_new();
        p = t;
    }
    unlock();
}