Page 122 - DCAP103_Principle of operating system

Unit 4: Process Management-III

2. To avoid the race condition, the number of processes that may be simultaneously inside Notes
their critical section is
( a) 8 (b) 1
( c) 16 (d) 0
3. A critical region

( a) is a piece of code which only one process executes at a time
( b) is a region prone to deadlock

( c) is a piece of code which only a finite number of processes execute
( d) is found only in Windows NT operation system
4. The solution to Critical Section Problem is: Mutual Exclusion, Progress and Bounded
Waiting.
( a) The statement is false. (b) The statement is true.
( c) The statement is contradictory. (d) None of the above

4.4 Safety-Critical Operating Systems

The successful design of safety-critical systems is difficult and demands significant attention to
detail. Fortunately, an operating system’s emphasis on protection and resource guarantees can
make the job of application developers less arduous.
Whether you are designing a telecom switch, a piece of medical equipment, or one of the many
complex systems aboard an aircraft, certain critical parts of the application must be able to
operate under all conditions. Indeed, given the steadily increasing speed of processors and the
economically-driven desire to run multiple applications, at varying levels of criticality, on the
same processor, the risks continue to grow. Consider a blood gas analyzer used in an intensive
care unit. The analyzer may serve two distinct purposes. First, it monitors the level of oxygen
and other gasses in the patient’s bloodstream, in real time. If any monitored gas reaches a
dangerously low or high level, the analyzer should produce an audible alarm or take some
more direct, intervention, action. But the device may have a second use, offering a historical
display of gas levels for “offline” analysis. In such a system, data logging, data display, and
user interface threads may compete with the critical monitoring and alarm threads for use of
the processor and other resources. In order for threads of varying importance to safely coexist
in the same system, the operating system that manages the processor and other resources must
be able to properly partition the software to guarantee resource availability. The key word here
is guarantee. Post-design, post-implementation testing cannot be counted on. Safety-critical
systems must be safe at all times.
4.4.1 Terminology

The following terms are used in this article:
• Thread: A lightweight unit of program execution

• Process: A heavyweight unit consisting primarily of a distinct address space, within which
one or more threads execute
• Kernel: The portion of an operating system that provides core system services such as
scheduling, thread synchronization, and interprocess communication

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