Question $5[20$ Marks$]$

Message buffers and message queues can be eliminated if processes exchange messages by rendezvous. In this scheme, a sender tries to find whether an intended receiver is waiting for its message. If so$,$ it copies the message to the receiver's address space and unblocks the receiver. If not, it waits. When the receiver runs, it tries to find a waiting sender which has message for it$.$ If so$,$ it copies the message and unblocks the sender$.$ Otherwise, it waits.

a$)$ Prove that, in a uniprocessor kernel, both sender and receiver wait for each other cannot occur.

$[10]$

b$)$ In a multiprocessor kernel, processes may run on separate processors in parallel. Can process rendezvous still work? Justify your answer.

Question $6[20$ Marks$]$

Device a memory compaction algorithm for the real mode MTX kernel. In kmalloc$(),$ if there is not enough memory and there are multiple holes, move all the process images to the high end of memory and try to allocate memory again. Note that, if a process image is moved, its saved segment registers in both the proc and user mode stack must be adjusted to suit the new segments.

Question $7[20$ Marks$]$

Assume P$1$ is a process which hops from segment to segment. Initially, P$1$ runs in the segment $\backslash (0\backslash$times $2000\backslash ).$ By a hop $($u$16$ segment$)$ syscall, it enters kernel to change segment. When it returns to Umode, it returns to an IDENTICAL Umode image but in a different segment, e$.$g$.\backslash (0\backslash$times $4000\backslash ).$ When P$1$ tries to change its Umode segment, the target segment may already be occupied by another process. If so$,$ the original process must be evicted to make room for P$1.$

Devise an algorithm for the hop$()$ syscall. In your algorithm, devise a technique that would allow P$1$ to move into a segment without destroying the original process in that segment.