lec3: Process Management 2018-2109

Process Management
A process can be thought of as a program in execution. A process will need certain resources — such as CPU time, memory, files, and I/O devices —to accomplish its task. These resources are allocated to the process either when it is created or while it is executing.
A process is the unit of work in most systems. Systems consist of a collection of processes: Operating-system processes execute system code, and user processes execute user code. All these processes may execute concurrently(parallel).
Although traditionally a process contained only a single thread of control as it ran, most modern operating systems now support processes that have multiple threads.
The operating system is responsible for the following activities in connection with process and thread management: the creation and deletion of both user and system processes; the scheduling of processes; and the provision of mechanisms for synchronization, communication, and deadlock handling for processes.
Table of Contents
1 PROCESSES 2
1.1 PROCESS CONCEPT 2
1.1.1 The Process 3
1.1.2 Process State 4
1.1.3 Process Control Block 5
1.1.4 Threads ? 6
1.2 PROCESS SCHEDULING 7
1.2.1 Scheduling Queues 7
1.2.2 Schedulers 9
1.2.3 Context Switch 10
1.3 OPERATIONS ON PROCESSES 10
1.3.1 Process Creation 10
1.4 SUMMARY 11

1 Processes
Early computer systems allowed only one program to be executed at a time. This program had complete control of the system and had access to all the system’s resources. In contrast, current-day computer systems allow multiple programs to be loaded into memory and executed concurrently. This evolution required firmer control and more compartmentalization of the various programs, and these needs resulted in the notion of a process, which is a program in execution. A process is the unit of work in a modern time-sharing system.
A system consists of a collection of processes: operating- system processes executing system code and user processes executing user code. Potentially, all these processes can execute concurrently, with the CPU (or CPUs) multiplexed among them. By switching the CPU between processes, the operating system can make the computer more productive.
CHAPTER OBJECTIVES
- To introduce the notion of a process—a program in execution that forms the basis of all computation. ?
- To describe the various features of processes, including scheduling, creation and termination, and communication. ?