Operating Systems

Team:Jonathan Arturo Alvarado Mata   1441616Obed David  Guevara Ibarra        1447478

Carlos Eduardo Triana Sarmiento    1412573

Blog:http://os-ocj.blogspot.com/

First Point

 Explain how to solve unbounded-buffer producer-consumer with locks.  Discuss the quality of the proposed solution.

what we did?...

We use an array as global variable, this array contain the number of items. We use this array to control the producer and the consumer, because if the array is full the producer stops producing and if the array is empty the consumer stops consuming

Also we use two threads, one for the consumer and the other for the producer.

what we did?...

The assignment consists in implementing locks to the producer consumer problem. So we have to declare a lock as a global variable, which controls the threads activity.This is important to remember.... Only the thread that acquired the lock can release it

CODELOCK *L1;CONDITION *C

PRODUCER(){        WHILE(1){// try to aquire the lockIF(L1->TRYAQUIRE()){                         // if the array is full, lets wait                         // if it isn’t, continue...                           WHILE(ARRAY == FULL){                                     C->WAIT(L1)                                        }                  // increase the number of items in the array                 C-> SIGNAL(); // Enables the waiting threads                 L1->RELEASE(); } // end of if             } // end of  while       } // end of the function producer

CONSUMER(){while(1){// try to aquire the lockif(l1->TRYAQUIRE()){// if the array is empty, wait                 // if it isn’t, continue...                  WHILE(ARRAY == EMPTY){                             C->WAIT(L1);                                        } // decrease the number of items in the array             CONSUME();                     C-> SIGNALl(); // Enables the waiting thread                     L1->RELEASE();         } // end of if     } // end of while} //end of function consumer

void main(){L1 = new lock(“L1”);C = new condition(“C”);Thread *t = new Thread(“producer”);  t->Fork(producer, 1);Thread * t= new Thread(“consumer”);t->Fork(consumer, 1);}end main

Second Point  

Explain how to detect and eliminate deadlock in the dinning philosophers problem.

The solution...

* This is the solution

When a philosopher has a fork waits a random time to get the second fork. If in that time is not free the second fork, release the one he has and go back to the queue

If a philosopher "A" release a fork (because he has eaten or because he waited too long with a fork in hand) but still want to eat, getting back on line to the fork. Basically we follow this concept and that's how we make the code

CODEPhilosophers[N];    //Array to store the philosophersLock *L1 // Only two philosophers can try to get 2 forksLock *L2

void philosopher (i){        WHILE(true){        think(); //All the philosophers start waiting        take_forks(i);     } //End of while} //End of function

void take_forks(int i){    Look_for_Locks();    Get_Forks();    Eat();    Drop_Forks();     L1->release() || L2 ->release();   //release the lock that the philosophers has     philosopher return to the queue     } //End of function

 void Look_for_Locks(){    IF(L1->tryaquire() || L2 -> tryaquire()){         if one is available        return to  take_forks    }ELSE{ // if not         wait some time        look if one lock is available and try to get it        if no lock is available            L1-> release() || L2 -> release()        philosopher return to the queue    }//end else}

  void Get_Forks(){    Look for forks;    if(fork == 1 || fork == 0) // if no Lock is available or if only got one        wait some time        look if forks are available and try to get one or two        if (fork == 2){             return to take_forks    }else{ // if doesn’t get the fork it need        drop fork        L1-> release() || L2 -> release()   // release the lock that the philosophers has        philosopher return to the queue    }else{return to take_forks}}

Bibliography

*Operating Systems-Design and Implementation, Second Edition Author: Andrew S. Tanenbaum and Albert S. Woodhull * http://www.isi.edu/~faber/cs402/notes/lecture7.html *http://www.4coders.com/index.php?modulo=contenido&op=detalle&tipo=c&id=83http://www.4coders.com/index.php?modulo=contenido&op=detalle&tipo=c&id=83 *http://es.wikipedia.org/wiki/Problema_de_la_cena_de_los_fil%C3%B3sofos