A multithreaded web server uses a cache to avoid disk reads for frequently accessed pages. When a request is received, a worker thread first checks the cache and will perform a disk read only if the page is not found in the cache. Kernel-level threads should be used instead of user-level threads to allow preemption for better response times under heavy loads.

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fetching these pages from the disk. Whenever a request for a web page is received, a worker
thread will first check the cache. A disk read u,ill only be performed if the page is not in the
cache. You have been told that u5gllqv€Llhrygls are being used for the worker threads. Should
kernelJevel threads be used instead? Justi r answer. marks
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2. AACS5214 COMPUTER OPER]TTING SYSTEMS 2O1Oi2O11
Q3. A real-time system has 3 periodic tasks as shown in the table below:
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Can each of the policies below pro{qce a feasible schedule? Justif, your answers with Gantt
charts s howin g thi sch edu le between (fl and/O?f .
r Rate-Monotonic schedvling (RMS)
o Earliest-Deadline-First scheduling (EDF) (8 marks)
Rate-Monotonic schgdullne
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3. jr
AACS5214 COMPUTER OPERATING SYSTEMS 2010/2011
Q4. Consider a solution to the prgduqer-copsuqrer problem with the use of semaphores as given
below. The variabl.g, semapho..r. ,(- *,
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Producer Consumer
do{ do{
// produce an item wait (full);
wait (empty); wait (mutex);
wait (mutex); // remove an item from buffer
// insert item into a buffer of size N signal (rnutex);
signal (mutex); signal (empty);
qignal (full); // consume item
while (TRUE); while (TRUE):
(i) What should be the initial value of the empty semaphore? Explain the purpose of the S G
(empty) statement in thez.Producer process-jupport your answer by explaining the funciffi
of the wait ogeration)N{th the use of pseudocode. (6 marks)
Initial value of e
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AACS5214 COMPUTER OPERr{TING SYSTEMS 2010/2011
(iii) Evaluate the use of semaphores to solve the producer-consumer problem. (5 marks)
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