CS354 Spring 2007

Final Exam


Name: ____________________________________________









Question
 Max
 Grade
T/F
10 pts.
1-5
 20 pts.
6-10
 20 pts.
11.
10 pts.
12.
 10 pts.
13.
 15 pts.
14.
 15 pts.
Total:
 100 pts.























Part 1. Answer True/False (T/F) (1 point each)

____ The page-table register is updated every time there is a context switch from one thread to another.
____ There is a stack for every thread in the process.
____ mmap() returns NULL if there is an error.
____ Two VM pages in the same process could map to the same physical page.
____ The backing-store of the Stack is swap space.

____ sbrk(0) will return a pointer to the end of the heap.
____ An object returned by malloc could have an address that ends in "2" .
____ cond_signal could wake up more than one thread.
____ The stack of one thread could potentially be modified by another thread.
____ mmaped memory that is modified is immediately updated in the mapped file.

Part 2. Short Questions

1. (4 pts) Enumerate the memory sections of a program  that use swap space as backing store and when.
 
 
 
 
 
 

2. (4 pts) Enumerate the fields of an i-node.
 
 
 
 
 

 
 

3. (4 pts)  Give an example in "C" of a premature free.
 
 


 
                Give an example in "C" of a memory leak.


 
 

4. (4 pts) Explain how you could modify your memory allocator to detect "memory smashing".






5. (4 pts) Explain how VM memory speeds up the allocation of  zero-initialized memory for stack or heap.





6. (4 pts) Explain how the modified clock algorithm works to approximate LRU.






7. (4 pts) What are the advantages and disadvantages of hard links vs. symbolic links?






8. (4 pts)  Explain how VM memory speeds up the execution of fork().






9. (4 pts)  Explain why the malloc libraries may have problems return memory back to the OS.








10. (4 pts). Explain what is internal fragmentation and external fragmentation.







Part 3 Long Questions. 

11. (10 pts) Write a program "grepsortout arg1 arg2 arg3" that  executes the shell command "grep arg1 arg2 | sort > arg3" in the program using fork, execvp, pipe, dup2, and any other call you need. arg1, arg2, and arg3 are passed through argv. Print any error to stderr and print a diagnostic using perror().
int main( int argc, char ** argv) {




























}
 


12. (10 pts)  From your lab5,  write the C++ function
<>int RPCServer::RPCServer( char * sharedFileName );
int RPCServer::RPCServer( char * sharedFileName ) {






















}
 


13. (15 pts) From lab7 from the method "int void Allocator::freeObject( void * ptr )" write the part that checks if the object at the left of "ptr" is free and coalesces it if necessary. If you need helper functions also include them in your implementation. Note: Only write this part of the code.

void
Allocator::freeObject( void * ptr )  {
   ... other code ...

 
  // IMPORTANT: Only write this part of the code of freeObject

  // Check if the object at the left of "ptr" is free and
  // coalesces it if necessary. Write all the steps to accomplish this.
  // If the object is coalesced, "ptr" should be updated to point
  // to the beginning of the coalesced object.














< style="font-family: monospace;">  ..other code ..

}
 

 
14. (15 pts) Write a class WaitForAlert that allows threads to wait for an alert until an alert is produced. Alerts have names of type (char *). A thread calling waitForAlert(alertName) will wait until another thread calling signalAlert(alertName) with the same alertName is called. For example, multiple threads can call waitForAlert("aaaa") and all these threads will block until  another thread calls signalAlert("aaaa"). If signalAlert(alertName) is called and no threads are waiting for this alertName, the signalAlert() call will be ignored. IMPORTANT: Use condition variables.
class WaitForAlert {
// Add your member variables here




public:
WaitForAlert();
void waitForAlert(const char * alertName);
void signalAlert(const chat *alertName);
};

WaitForAlert::WaitForAlert()
{







}

void WaitForAlert::waitForAlert(const char * alertName)
{









}

void WaitForAlert::signalAlert(const chat *alertName)
{











}