2020/10/26 下午7:17OS Fall 2020 Midterm Exam
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[ 1, 1 ]
[ 1, M ]
[ 1, X ]
[ M, 1 ]
[ X, 1 ]
[ M , X ]
[ X , M ]
[ M, M ]
[ X, X ]
insu,cient information to answer this question
OS Fall 2020 Midterm Exam
Given is an operating system that only suppo!s the user-level threading model
(M:1) but NOT the kernel level (1:1) . A clever programmer programmed her
application using threads. When this program is run on a system with
cpus, what is the combination of "[ maximum concurrency , maximum parallelism
]" (see possible answers below) this application can achieve when M is
signi"cantly higher than X ? [ 4 points ]
2020/10/26 下午7:17OS Fall 2020 Midterm Exam
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We have talked at length in class about the di#erences between interrupts,
systemcalls (traps) and exceptions. Provided are a few examples of events that
trigger an entry into the OS kernel. Each row should only have one answer. A
correct answer is 1pt an incorrect answer is -0.5. [ 8 points ]
Interrupt Systemcall Exception Unsure
User hits
keyboard
IO device
completed a disk
read
Scheduler
quantum expires
Process issues
pipe()
Process issues
read() on a Hle
Process stores to
write protected
area
Thread issues a
division by zero:
Loat x = 3.14 /
0.0
Thread
dereferences a
NULL ptr : int x =
*((int*)NULL;;
2020/10/26 下午7:17OS Fall 2020 Midterm Exam
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fork() and exec() are two fundamental system calls. Identify whether the
de"nition/prope!y described is true or false (must choose) or unsure/unmarked.
Correct row is 1 pt, an incorrect row leads to ½ pt deduction or 0 pts for blank or
"Unsure". [ 8 points ]
True False Unsure
exec() uses copy-on-
write semantics
fork() return code
identiHes whether
parent or child
fork() creates a
whole new process
fork() does nothing
unless combined
with exec()
exec() returns only on
error
exec() replaces the
program of the
currently running
process
exec() creates
execution unit and
then forks a new
process.
fork() creates only a
new address space
2020/10/26 下午7:17OS Fall 2020 Midterm Exam
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Batch Job
Process
Address Space
Thread
Task
Interactive Job
TCB
PCB
Address Space
Process Stack
Process Heap
No saving required since registers are virtualized in the CPU
Given is a multi-threading capable Operating System suppo!ing the 1:1
threading model. Which of the following entities does the CPU scheduler select
for execution ? [ 2 points ]
Given is a multi-threading capable Operating System suppo!ing the 1:1
threading model. During a kernel context switch (e.g. due to preemption or
blocking on I/O where is the state such as registers saved ? [ 3 points ]
2020/10/26 下午7:17OS Fall 2020 Midterm Exam
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mutex + mutex-exclusive
mutex + counting
binary + non-binary
bounded-buffer + binary
counting + non-binary
mutex + bounded-buffer
There are two types of semaphores. Select the one that identi"es the correct
names of those types as used in class. [ 3 points ]
2020/10/26 下午7:17OS Fall 2020 Midterm Exam
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struct { int value; List waiting; }
struct { int value; Liststruct { int value; List consumers; }
struct { int pvalue; int cvalue; List producers; List; }
struct { int value, List users; }
struct { int value; List users; }
struct { int value; List producers; }
struct { int value; List producers; }
struct { int pvalue; int cvalue; List producers; List; }
struct { int value; List consumers; }
A semaphore is implemented using multiple members. Assume a multi-threading
capable operating system. Select the most correct de"nition, paying a%ention to
the functionality implied by the name of the struct members [ 4 points ]
2020/10/26 下午7:17OS Fall 2020 Midterm Exam
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unsupervised vs supervised
user vs kernel
fork vs exec
exec vs fork
unsupervised vs priviliged
problem vs no-problem
priviliged vs unpriviliged
kernel vs user
A CPU typically operates in two di#erent modes, namely at the application level
and at the operating system level. What are these two modes most commonly
called. Pick the most appropriate pair where the le& side identi"es the
application and the right side identi"es the operating system mode. [ 2 points ]
Given the schedulers implemented in lab2 (FCFS, LCFS, SRTF, RR, PRIO,
PREPRIO), which scheduler is the best for the stated system objective in each
row [ 8 points ]
FCFS LCFS SRTF RR PRIO PREPRIO
same fairness
but preempt
after a
speciHed
quantum
always make
sure the
highest
2020/10/26 下午7:17OS Fall 2020 Midterm Exam
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priority job
runs
System/Job
throughput
with earlier
ready jobs
Hrst
system/job
throughput
with recent
ready jobs
Hrst
priorities of
processes are
taken into
account, but
number of
context
switches
should be
small
smallest
average
response time
for io-bound
processes
same
perceived
fairness
among jobs
smallest
average
waiting time
across all
processes
,
2020/10/26 下午7:17OS Fall 2020 Midterm Exam
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Synchronization and Parallelization
Synchronization and Event NotiHcation
Event NotiHcation and Parallelization
None of the three operations (Synchronization, Parallelism or Event NotiHcation)
All of the three operations (Synchronization, Parallelism or Event NotiHcation)
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Locks, Semaphores, Conditions Variables and Monitors suppo! which of these
operations? Select the most appropriate answer [ 3 points ]
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