Page 116 - DCAP103_Principle of operating system

Unit 4: Process Management-III

Notes
4.6.17 Several Instances of a Resource Type
4.6.18 Detection-Algorithm Usage
4.6.19 Recovery from Deadlock
4.6.20 Process Termination
4.6.21 Abort All Deadlocked Processes
4.6.22 Abort One Process at a Time Until the Deadlock Cycle is Eliminated
4.6.23 Resource Preemption

4.7 Summary
4.8 Keywords
4.9 Review Questions

4.10 Further Readings
Objectives

After studying this unit, you will be able to:
• Explain meaning of process management-III

• Understand concept of critical section
• Discuss the critical-section problem
• Explain way to handle critical-section problem

• Understand safety-critical operating systems
• Discuss semaphores
• Explain deadlock concept and handling

Introduction

A process is a program in execution. A process must have system resources, such as memory
and the underlying CPU. The kernel supports the illusion of concurrent execution of multiple
processes by scheduling system resources among the set of processes that are ready to execute.
On a multiprocessor, multiple processes may really execute concurrently. This unit describes the
composition of a process, the method that the system uses to switch between processes, and the
scheduling policy that it uses to promote sharing of the CPU. It also introduces process creation
and termination, and details the signal facilities and process-debugging facilities.

4.1 Concept of Critical Section

4.1.1 Basic Concept

If a data item is shared by a number threads, race conditions could occur if the shared item is
not protected properly. The easiest protection mechanism is a lock. In general, if a set of data
items must be protected so that at any time there is no more than one thread can have access
to it, we can associate the set of data items with a lock. The use of locks is actually very easy.
For every thread, before it accesses the set of data items, it acquires the lock. Once the lock is
successfully acquired, the thread becomes the owner of that lock and the lock is locked. Then,
the owner can access the protected items. After this, the owner must release the lock and the

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