OS concept - Synchronization

Synchronization is an important concept in Operating System. Producer/Consumer and Reader/Writer are two examples of synchronization problems. The following is the sample codes for them. 

Producer and Consumer

int buf[N], in = 0, out = 0;

sem filledslots = 0, emptyslots = N, mutex = 1;

Producer()

{

    wait(emptyslots);   //synchronization start

    wait(mutex);        //critical section start

    Produce(buf[in]);

    in = (in + 1) % N;

    signal(mutex);      //critical section end

    signal(filledslots);//synchronization end

}

Consumer()

{

    wait(filledslots);  //synchronization start

    wait(mutex);        //critical section start

    Consume(buf[out]);

    out = (out + 1) % N;

    signal(mutex);      //critical section end

    signal(emptyslots); //synchronization end

}

Reader and Writer

int n = 0;

sem mutex = 1, RW = 1;

Reader()

{

    wait(mutex);   // lock reader

    n++;

    if (n == 1)

        wait(RW);  // lock first reader when there is a writer

    signal(mutex);

    Read();

    wait(mutex);

    if (n == 1)

        signal(RW);

    n--;

    signal(mutex);

}

Writer()

{

    wait(RW);      // wait if at least one reader is reading

    Write();

    signal(RW);

}