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Problem 4 (30 pts) a) (15 pts) Three processes share four resource units that can be reserved and released only one at a time. Each process acquires and releases resources over time but only needs a maximum of two resource units at any one time. Deadlock can not occur. Why b) (15 pts) Consider a system consisting of m resources of the same type, being shared by n processes. Resources can be requested and released by processes only 1 at a time. Show that the system is deadlock free if the following two conditions hold: (I) The max need for each process is between 1 and m resources. (II) The sum of all max needs is less than n + m. Problem 5 (15 pts) In lecture we said that, if the semaphore operations Wait and Signal are not executed atomically, then mutual exclusion may be violated. Assume that Wait and Signal are implemented as below: void Wait (Semaphore S) { while (S.count
Problem 6 (25 Points) Consider a system that has W workers and M managers that continuously enter and leave an office. Work can only be done in teams consisting of 1 manager and 2 workers in the office. The detailed requirements are: • Managers arrive to a FCFS queue, and workers arrive to their own FCFS queue. • When the manager at the front of the queue is ready, he/she picks the next two workers for his team and tells them to begin working. Then, the next manager can form his/her team in a similar manner. • Workers tell their manager when they are done working and leave immediately. • A manager does not leave until all team members have said they are leaving. • After work is completed, the team members leave for a random amount of time before re turning. a) Describe the synchronization for the manager process by writing the manager process in terms of the counting semaphore primitives Signal() and Wait() and the semaphore and variable declarations. Note: You do not need to give the worker process code; i.e., you can assume that the worker process is given. b) Describe the use of each semaphore and the general logic of the manager process. You can do that using comments in your code. HINT: (Note: You may use the following skeleton.) struct { int manager; int worker[2]; int n=0; } newTeam; // shared // manager of new team // which workers are forming a new team // how many entries in worker[2] ... semaphore definitions ... Page 3 of 4
Page 1: CS 1901473 Operating Systems; Exam

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