Name: ____________________________________________

____ Most of the CPU  time is spent in user mode.
____ a.out is an executable file format used in early versions of Windows.
____ The backing-store of the Text segment is swap space.
____ The stack of one thread could potentially be modified by another thread.
____ Premature frees are a serious problem in short lived programs.

____ A page size has to be a power of 2.
____ The page table register is always updated during a context switch.
____ By default, when a thread calls mutex_lock for the same lock twice, the second mutex_lock call will be ignored.
____ All pages in physical memory that are replaced are written back to the disk.
____ The call realloc( NULL, 100) will cause a SEGV.

____ calloc( 8, 1 ) allocates 8 bytes initialized with 1s.
____ BEST FIT is faster than FIRST FIT.
____ Copy on write is used during fork().
____ An object returned by malloc could have an address like 0x100280.
____ The order of mutex_unlock()'s could lead to deadlocks.

____ Most processes in a system are in wait state.
____ Non-accessed pages are prefered for replacement instead of modified pages.
____ A free list that has two blocks of 20 and 80 bytes has a fragmentation of 80%.
____ A call to fork() by a process that has two POSIX threads will create a child process with two threads.
____ During starvation a thread waits for a resource or mutex lock that may never be available.
 

Part 2. Short Questions

2. (4 pts) A parent process P1 calls fork() and creates a child process P2. Explain step by step what the OS will do when a page is modified by process P1.
 
 
 
 
 
 
 
 
 

3. (4 pts) Explain how the clock algorithm for page replacement works. Explain how it is improved using also the modify bit.
 
 
 
 
 
 
 
 

4. (4 pts) Give one example of a premature free?

 

 
 
     Give one example of a memory leak 
 
 

5. (4 pts) Assume that we the allocator described in project 7 is used with the following code:

    int * a = (int *) malloc( sizeof(int) );
    int * b = (int *) malloc( sizeof(int));
    b[ 0 ] = 3;
    a[ 1 ] = 5;
    printf( "b=%d\n", b[0] );
    free( b );

    What is  the value printed?
     
   

     Explain what is going to happen during the free() call.

6. (5 pts) The following three threads have access to six databases. Each database has its own mutex lock.
Could the following threads enter in a deadlock? If that is the case draw the graph that shows the loop that represents this deadlock, and draw in the right side the code that could prevent the deadlock. Give specific mutex numbers when drawing the graphs
If the threads cannot enter into a deadlock, give an alteration of the the mutex_lock call sequence that may lead to a deadlock and draw a graph with the loop that represents this deadlock.

thread1()
{
    for ( int i = 0; i < 10000; i++ ) {
        for ( int j = 0; j < 2; j++ ) {
           for ( int k = 0; k < 2; k++ ) {
      mutex_lock( &mutex[ j ]);
      mutex_lock( &mutex[ k ]);

            // Call some code

      mutex_unlock(  &mutex[ j ]);
      mutex_unlock(  &mutex[ k ]);
     }
    }

  }
}

thread2()
{
    for ( int i = 0; i < 10000; i++ ) {
          for ( int j = 0; j < 2; j++ ) {
             for ( int k = 0; k < 2; k++ ) {
        mutex_lock( &mutex[ j ]);
        mutex_lock( &mutex[ k ]);

              // Call some code

        mutex_unlock( &mutex[ j ]);
        mutex_unlock( &mutex[ k ]);

      }
    }

   }
}

struct List {
  int val;
  int next;
};

struct List * head = NULL;

// More variables

void insert( int val )
{

  List tmp = new List;

  tmp->val = val;

  tmp->next = head;

  head = tmp;

}

Struct List * removeFirst()
{

  List tmp = head;

  head = tmp->next;

}

Part 3 Long Questions. (10 points each)