ECS 150, Operating Systems Fall Quarter 2008
Program 4
Due Date: December 2, 2008 Points: 100
Program
1. (100 points) The MINIX kernel does not implement user-level semaphores. Your task in this project is to do so.
The semaphore system calls have the following interface:
#include <minix/semaphore.h>
int semup(int semaphorenumber);
int semdown(int semaphorenumber);
int seminit(int semaphorenumber, int value);
int semdestroy(int semaphorenumber);
int semstatus(int semaphorenumber, int *value, int *numblocked);
In all the above system calls, semaphorenumber is the number of the semaphore (0 through 9). In seminit,
the initial value of the semaphore is set to value. In semstatus, the current value of the semaphore is returned
in value, and the number of processes blocked on that semaphore is returned in numblocked.
The system call seminit creates the semaphore and returns 0 if the semaphore does not exist. The initial
value is set to value. It returns โ1 if the semaphore exists. The system call semdestroy deletes the given
semaphore and returns 0. If any processes are blocked on it, though, it returns โ1 and does not delete the
semaphore. All other calls return 0 on success and โ1 on failure.
Please implement the producer-consumer problem to verify your semaphores work correctly. Your program
must use the semaphores to synchronize accesses to the bounded buffer (to be implemented as a file) and the
necessary counters (also kept in a file). The program will open and initialize the files, initialize the semaphores,
and then fork a specified number of producer and consumer processes which produce or consume a specified
number of items.
Hint: Implement these in the memory manager (MM), where tasks can be easily blocked and restarted. Note
that you do not need a synchronization mechanism within the kernel to protect the semaphore structures because
while the memory manager is running, no other process will run..
Extra Credit
1. (20 points) Implement appropriate errno codes and perror strings to describe errors in the above system
calls in more detail.
Write a program to demonstrate these work.
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