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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 208
CHAP. 2
PROBLEMS
177
37.
Suppose that we have a message-passing system using mailboxes. When sending to a
full mailbox or trying to receive from an empty one, a process does not block. Instead,
it gets an error code back.
The process responds to the error code by just trying again,
over and over, until it succeeds. Does this scheme lead to race conditions?
38.
The CDC 6600 computers could handle up to 10 I/O processes simultaneously using
an interesting form of round-robin scheduling called processor sharing.
A process
switch occurred after each instruction, so instruction 1 came from process 1, instruc-
tion 2 came from process 2, etc. The process switching was done by special hardware,
and the overhead was zero.
If a process needed
T
sec to complete in the absence of
competition, how much time would it need if processor sharing was used with
n
proc-
esses?
39.
Consider the following piece of C code:
void main( ) {
fork( );
fork( );
exit( );
}
How many child processes are created upon execution of this program?
40.
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
twice in the list?
Can you think of any reason for allowing this?
41.
Can a measure of whether a process is likely to be CPU bound or I/O bound be deter-
mined by analyzing source code? How can this be determined at run time?
42.
Explain how time quantum value and context switching time affect each other, in a
round-robin scheduling algorithm.
43.
Measurements of a certain system have shown that the average process runs for a time
T
before blocking on I/O.
A process switch requires a time
S
, which is effectively
wasted (overhead). For round-robin scheduling with quantum
Q
, give a formula for
the CPU efficiency for each of the following:
(a)
Q
=
∞
(b)
Q
>
T
(c)
S
<
Q
<
T
(d)
Q
=
S
(e)
Q
nearly 0
44.
Five jobs are waiting to be run. Their expected run times are 9, 6, 3, 5, and
X
. In what
order should they be run to minimize average response time?
(Your answer will
depend on
X
.)
45.
Five batch jobs.
A
through
E
, arrive at a computer center at almost the same time.
They have estimated running times of 10, 6, 2, 4, and 8 minutes.
Their (externally de-
termined) priorities are 3, 5, 2, 1, and 4, respectively, with 5 being the highest priority.
For
each of the following scheduling algorithms, determine the mean process
turnaround time. Ignore process switching overhead.
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