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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
Showing 501-502 out of 1137
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 501
470
DEADLOCKS
CHAP. 6
41.
Program a simulation of the banker’s algorithm. Your program should cycle through
each of the bank clients asking for a request and evaluating whether it is safe or unsafe.
Output a log of requests and decisions to a file.
42.
Write a program to implement the deadlock detection algorithm with multiple re-
sources of each type. Your program should read from a file the following inputs: the
number of processes, the number of resource types, the number of resources of each
type in existence (vector
E
), the current allocation matrix
C
(first row, followed by the
second row, and so on), the request matrix
R
(first row, followed by the second row,
and so on).
The output of your program should indicate whether there is a deadlock in
the system. In case there is, the program should print out the identities of all processes
that are deadlocked.
43.
Write a program that detects if there is a deadlock in the system by using a resource al-
location graph. Your program should read from a file the following inputs: the number
of processes and the number of resources.
For each process if should read four num-
bers: the number of resources it is currently holding, the IDs of resources it is holding,
the number of resources it is currently requesting, the IDs of resources it is requesting.
The output of program should indicate if there is a deadlock in the system. In case
there is, the program should print out the identities of all processes that are deadlocked.
44.
In certain countries, when two people meet they bow to each other. The protocol is that
one of them bows first and stays down until the other one bows. If they bow at the
same time, they will both stay bowed forever. Write a program that does not deadlock.
Page 502
7
VIRTUALIZATION AND THE CLOUD
In some situations, an organization has a multicomputer but does not actually
want it. A common example is where a company has an email server, a Web server,
an FTP server, some e-commerce servers, and others. These all run on different
computers in the same equipment rack, all connected by a high-speed network, in
other words, a multicomputer. One reason all these servers run on separate ma-
chines may be that one machine cannot handle the load, but another is reliability:
management simply does not trust the operating system to run 24 hours a day, 365
or 366 days a year, with no failures. By putting each service on a separate com-
puter, if one of the servers crashes, at least the other ones are not affected. This is
good for security also. Even if some malevolent intruder manages to compromise
the Web server, he will not immediately have access to sensitive emails also—a
property sometimes referred to as
sandboxing
.
While isolation and fault tolerance
are achieved this way, this solution is expensive and hard to manage because so
many machines are involved.
Mind you, these are just two out of many reasons for keeping separate ma-
chines. For instance, organizations often depend on more than one operating sys-
tem for their daily operations: a Web server on Linux, a mail server on Windows,
an e-commerce server for customers running on OS X, and a few other services
running on various flavors of UNIX. Again, this solution works, but cheap it is def-
initely not.
What to do? A possible (and popular) solution is to use virtual machine tech-
nology, which sounds very hip and modern, but the idea is old, dating back to the
471
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