Keys to Some of the Exercise questions
---------------------------------------

2. Specify the hardware support necessary for memory protection, and
explain briefly how it works.

The system should provide some kind of hardware support to keep track of 
which parts of memory are currently being used and by whom, to make sure 
that a process does not access the memory being used by other processes.
(Discused in Section 1.7)

3. State the correctness criteria for the producer-consumer problem. 

(1) No underflow: consumer must wait for producer to fill buffers.
(2) No overflow: producer must wait if all buffer space is in use.
(3) Only one process must manipulate buffer pool at once.

4. Write down a solution of the Producer-Consumer problem using
monitor. Let N be the buffer size.

Monitor Producer-Consumer
int buffer[N], item, count
condition full, empty

Put_it(item)
while (count == N) wait(full)
{put item into the buffer}
count = count + 1
if (count == 1) signal(empty)

Grab_it()
while (count == 0) wait(empty)
{get item from buffer}
count = count - 1
if (count == (N-1)) signal(full)

endmonitor

Producer
--------
while (true) 
{generate (item)}
Put_it(item)

Consumer
--------
while(true)
Grab_it()
{consume (item)}


6. Synchronization has two parts: mutual exclusion and scheduling.
Discuss how they are provided in monitors.

ME is autoimatically providede by the monitor lock.
Scheduling is provided by the condition variables.

7. Draw the state transision diagram of a process and indicate which 
transition can be incurred by wait and signal operations of a monitor.

Running -> Blocked: P or waiting for event
Blocked -> Ready: V or event occurs

8. In the semaphore solution of readers/writers, can OKToWrite
ever get greater than 1? What about OKToRead? Explain how it can 
(or cannot) happen.

OKToWrite cannot be great than 1. 
OKToRead can be great than 1.

9. In the monitor solution of readers/writers, is FIFO order guaranteed 
for Writers (i.e., the first writer who calls checkWrite will go into 
the database before other writers who call checkWrite later)?

FIFO is not guaranteed.

10. Regarding the monitor solution of readers/writers, 
if the first writer (P1) is inside the doneWrite procedure when the 
second writer (P2) arrives to the system, how far can it go within the 
checkWrite procedure?

P2 is not going anywhere; it is waiting for the monitor lock at 
the entrance of the monitor.