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Processes Management. 3.2 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Process Management A process is a program.

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Presentation on theme: "Processes Management. 3.2 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Process Management A process is a program."— Presentation transcript:

1 Processes Management

2 3.2 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Process Management A process is a program in execution. It is a unit of work within the system. Program is a passive entity, process is an active entity. Process needs resources to accomplish its task CPU, memory, I/O, files Initialization data Process termination requires reclaim of any reusable resources Single-threaded process has one program counter specifying location of next instruction to execute Process executes instructions sequentially, one at a time, until completion Multi-threaded process has one program counter per thread

3 3.3 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Process Management Activities Creating and deleting both user and system processes Suspending and resuming processes Providing mechanisms for process synchronization Providing mechanisms for process communication Providing mechanisms for deadlock handling The operating system is responsible for the following activities in connection with process management:

4 3.4 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Memory Management All data in memory before and after processing All instructions in memory in order to execute Memory management determines what is in memory when Optimizing CPU utilization and computer response to users Memory management activities Keeping track of which parts of memory are currently being used and by whom Deciding which processes (or parts thereof) and data to move into and out of memory Allocating and deallocating memory space as needed

5 3.5 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Storage Management File-System management Files usually organized into directories Access control on most systems to determine who can access what OS activities include  Creating and deleting files and directories  Primitives to manipulate files and directores  Mapping files onto secondary storage  Backup files onto stable (non-volatile) storage media

6 3.6 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Mass-Storage Management Usually disks used to store data that does not fit in main memory or data that must be kept for a “long” period of time Proper management is of central importance Entire speed of computer operation hinges on disk subsystem and its algorithms OS activities Free-space management Storage allocation Disk scheduling

7 3.7 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition I/O Subsystem One purpose of OS is to hide peculiarities of hardware devices from the user I/O subsystem responsible for Memory management of I/O including buffering (storing data temporarily while it is being transferred), caching (storing parts of data in faster storage for performance), spooling (the overlapping of output of one job with input of other jobs) General device-driver interface Drivers for specific hardware devices

8 3.8 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Process Concept An operating system executes a variety of programs: Batch system – jobs Time-shared systems – user programs or tasks Textbook uses the terms job and process almost interchangeably Process – a program in execution; process execution must progress in sequential fashion A process includes: program counter stack data section

9 3.9 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition The Process Multiple parts The program code, also called text section Current activity including program counter, processor registers Stack containing temporary data  Function parameters, return addresses, local variables Data section containing global variables Heap containing memory dynamically allocated during run time Program is passive entity, process is active Program becomes process when executable file loaded into memory

10 3.10 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Process in Memory

11 3.11 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Process State As a process executes, it changes state new: The process is being created running: Instructions are being executed waiting: The process is waiting for some event to occur ready: The process is waiting to be assigned to a processor terminated: The process has finished execution

12 3.12 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Diagram of Process State

13 3.13 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Process Control Block (PCB) Information associated with each process Process state Program counter CPU registers CPU scheduling information Memory-management information Accounting information I/O status information

14 3.14 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Process Control Block (PCB)

15 3.15 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition CPU Switch From Process to Process

16 3.16 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Process Scheduling Maximize CPU use, quickly switch processes onto CPU for time sharing Process scheduler selects among available processes for next execution on CPU Maintains scheduling queues of processes Job queue – set of all processes in the system Ready queue – set of all processes residing in main memory, ready and waiting to execute Device queues – set of processes waiting for an I/O device

17 3.17 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Representation of Process Scheduling

18 3.18 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Schedulers Long-term scheduler (or job scheduler) – selects which processes should be brought into the ready queue Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU

19 3.19 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Schedulers (Cont.) Short-term scheduler is invoked very frequently (milliseconds)  (must be fast) Long-term scheduler is invoked very infrequently (seconds, minutes)  (may be slow) The long-term scheduler controls the degree of multiprogramming Processes can be described as either: I/O-bound process – spends more time doing I/O than computations, many short CPU bursts CPU-bound process – spends more time doing computations; few very long CPU bursts

20 3.20 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Addition of Medium Term Scheduling

21 3.21 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Context Switch When CPU switches to another process, the system must save the state of the old process and load the saved state for the new process via a context switch. Context of a process represented in the PCB Context-switch time is overhead; the system does no useful work while switching The more complex the OS and the PCB -> longer the context switch

22 3.22 Silberschatz, Galvin and Gagne ©2011 Operating System Concepts Essentials – 8 th Edition Thanks


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