-"Second, an interrupt handler must not call any function that can
-sleep, which rules out thread_yield(), lock_acquire(), and many
-others. This is because external interrupts use space on the stack of
-the kernel thread that was running at the time the interrupt occurred.
-If the interrupt handler tried to sleep and that thread resumed, then
-the two uses of the single stack would interfere, which cannot be
-allowed."
+The alarm tests do not test to see if multiple threads are woken up if
+their timers have expired. That is, students can write a solution
+that just wakes up the first thread on the sleep queue rather than
+check for additional threads. Of course, the next thread will be
+woken up on the next tick. Also, this might be hard to test.