These are two sample questions that could have appeared in a 531 exam




A multiprocessor operating system provides spin locks using the following routines:


sp_lock(int x)    : locks x, and if x is already locked then the routine spins till the lock is obtained

sp_unlock(int x)  : unlocks x


We are provided with routines that do blocking and unblocking. These routines are re-entrant  are:


     block(queue Q):blocks the current process and places the PCB on Q

     unblock(queue Q):unblocks one process from Q


Now we want to define a barrier operation:

     barrier ( barriertype B);


To use the barrier, a field in B is initialized to the number of processes that synchronize on the barrier. Then each process calls the barrier and all block till the last process to arrive frees them all up.


Hint: You need to define the type barriertype, and this can be a struct with an int and a queue.



MPI is a message-passing package that can be thought of a library that supports the following functions:


         MPI_spawn(processor and arguments): create a process on a specified processor.

         MPI_Send(where and what)       :    send a message to a port

         MPI_Recv(from where and what):    receive a message from a port


The MPI package can be used to write concurrent or parallel programs that run on UMA machines as well as NUMA machines (as well as distributed systems - but we are not considering that in this question).


A.    Briefly, state how MPI is used on NUMA machines to write programs.


B.     Can parallel programs be written on UMA machines without the use of MPI. Show how, and describe what facility (other than MPI and regular sequential programming) would be needed.


C.     What are the advantages of using MPI on UMA machines (over the scheme outlined in your answer for (B)).


D.    What are the disadvantages of using MPI on UMA machines (over the scheme in (B)).