State the Readers and Writers Problem and write its semaphore based solution. Also describe the algorithm. Can the producer consumer problem be considered as a special xase of Reader/Writer problem with a single Writer(the producer and a single Reader (consumer) Explain.)

readers - writers : monitor begin readercout: interger; busy : Boolean; OKtoread , OKtowrite :

condition; procedure startread; begin if busy then OKtoread.wait; readercount :=readercount + 1;

OKtoread.signal; (*Once one reader can start, they all can *) end startend; procedure endread;

begin readercount: = readercount - 1; if readercount =0 then OKtowrite.signal; end endread;

procedure startwrite; begin if busy OR readercout !=0 then OKtowrite.wait; busy : = true; end

startwrite ; procedure endwrite; begin busy:=false; if OKtoread.queue then OKtoread.signal else

OKtowrite.signal; end OKtowrite.sigal; end endwrite; begin(*initialization*) readercount =0;

busy: false; end; end readers - writers;

The above code gives a solution to the readers priority problem using monitors. For

proper synchronization reader processes must call the startread procedure before

accessing the file and call the endread when the read is finished. Likewise, writer

processes must call startwrite before modifying the file and call endwrite when the write

is finished. The monitor users the Boolean variables busy to indicate whether a writer is

active and readercount to keep track of the number of active readers.

On invoking startread, a reader process is blocked and placed in the queue of the

OKtoread condition variable if busy is true Otherwise, the reader proceeds and performs

the following. The process increments the readercount, and activated a waiting reader, if

present, thought the OKtoread.signal operation. On the completion of access, a reader

invokes endread, where readercount is decremented. When there are no active readers,

the last exiting reader process performs the Oktowrite.signal operation to activate any

waiting writer.

A writer, on invoking start write, proceeds only when no other writer or readers are

active. The process sets busy to true to indicate that a writer is active. On completion of

the access, a writer invokes the end write procedure. The end write procedure sets busy to

false, indicating that no writer is active, and checks the OK to read queue for the presence

of waiting readers. If there is a waiting reader, the exiting writers queue. If a reader

otherwise it signals the writer queue. If a reader is activated in end write procedure, it

increments the reader count and executes the OK to read signal, thereby activating the next waiting reader in the queue. This process continues until all the waiting readers have been activated, during which processes trying to enter the monitor are blocked and join the monitor's entry queue. But, after all the readers waiting on the OK to read condition have been signed, any newly arrived readers will again access to the monitor before any waiting writers. In summary, the readers priority monitor, while not permitting a new writer to start when there is a reader waiting, permits any number of readers to proceed, as long as there is at least one active reader.