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Synchronization

Producer and Consumer with Semaphores​

  • Easy to implement, one sema for consumer and producer
  • But not the solution we are approaching to? There are some ambiguity on whether the semaphore puts the threads to sleep or is forced to spin-wait (thus makes it busy-waiting and not recommended)
Producer waits for the vending machine to be empty (&emptySlots semaphore > 0)
    waits for the machine to be free, lock it up (&mutex)
        enqueue
    release the machine (release &mutex) 
    up sema for fullslots

Consumer waits for the vending to be fully? slotted (&fullSlots semaphore > 0) 
    waits for the machine to be free, lock it up (&mutex)
        dequeue 
    release the machine (release &mutex)
    up sema for empty

*mutex semaphores ensures critical section integrity

Producer and Consumer with monitors​

  • Monitor is a lock with zero or more conditional variables, and conditional variables are a queue of threads.