Description

• Write in a neat and legible handwriting
• Clearly explain the reasoning process
• Write in a complete style (subject, verb and object) Progamming exercises:
• Write a README file for each program
• Upload an archive with all the programs onto Canvas
Ex. 1 — Simple questions
1. A system has two processes and three identical resources. Each process needs a maximum of two resources. Can a deadlock occur? Explain.
3. A real-time system has four periodic events with periods of 50, 100, 200, and 250 msec each. Suppose the four events require 35, 20, 10, and x msec of CPU time, respectively. What is the largest value x for which the system is schedulable?
4. Round-robin schedulers normally maintain a list of all runnable processes, with each process occurring exactly once in the list. What would happen if a process occurred more than once in the list? Would there be any reason for allowing this?
5. Can a measure of whether a process is likely to be CPU bound or I/O bound be detected by analyzing the source code. How to determine it at runtime?
Ex. 2 — Deadlocks
Assuming three resources consider the following snapshot of a system.
Process Allocated Maximum Available
P1 010 753 332
P2 200 322
P3 302 902
P4 211 222
P5 002 433
1. Determine the content of the Request matrix.
2. Is the system in a safe state?
3. Can all the processes be completed without the system being in an unsafe state at any stage?
Ex. 3 — Programming
Implement the Banker’s algorithm.
Ex. 4 — Minix 3
How is scheduling handled in Minix 3? Provide clear explanations on how to find the information just by exploring the source code of Minix kernel.
Ex. 5 — The reader-writer problem
In the reader-writer problem, some data could be accessed for reading but also sometimes for writing. When processes want to read the data they get a read lock and a write lock for writing. Multiple processes could get a read lock at the same time while a write lock should prevent anybody else from reading or writing the data until the write lock is released.
To solve the problem we decide to use a global variable count together with two semaphores: count_lock for locking the count variable, and db_lock for locking the database. To get a write lock we can proceed as follows:

1. Explain how to get a read lock, and write the corresponding pseudocode.
2. Describe what is happening if many readers request a lock.
To overcome the previous problem we will block any new reader when a writer becomes available.
3. Explain how to implement this idea using another semaphore called read_lock.
4. Is this solution giving any unfair priority to the writer or the reader? Can the problem be considered as solved?