Bài giảng Hệ điều hành nâng cao - Chapter 3: Processes

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Chapter 3: Processes Operating System Concepts – 8th Edition Operating System Concepts – 8th Edition 3.1 Silberschatz, Galvin and Gagne ©2009
Chapter 3: Processes s Process Concept s Process Scheduling s Operations on Processes s Interprocess Communication s Examples of IPC Systems s Communication in Client-Server Systems Operating System Concepts – 8th Edition 3.2 Silberschatz, Galvin and Gagne ©2009
Objectives s To introduce the notion of a process -- a program in execution, which forms the basis of all computation s To describe the various features of processes, including scheduling, creation and termination, and communication s To describe communication in client-server systems Operating System Concepts – 8th Edition 3.3 Silberschatz, Galvin and Gagne ©2009
Process Concept s An operating system executes a variety of programs: q Batch system – jobs q Time-shared systems – user programs or tasks s Textbook uses the terms job and process almost interchangeably s Process – a program in execution; process execution must progress in sequential fashion s A process includes: q program counter q stack q data section Operating System Concepts – 8th Edition 3.4 Silberschatz, Galvin and Gagne ©2009
The Process s Multiple parts q The program code, also called text section q Current activity including program counter, processor registers q Stack containing temporary data 4 Function parameters, return addresses, local variables q Data section containing global variables q Heap containing memory dynamically allocated during run time s Program is passive entity, process is active q Program becomes process when executable file loaded into memory s Execution of program started via GUI mouse clicks, command line entry of its name, etc s One program can be several processes q Consider multiple users executing the same program Operating System Concepts – 8th Edition 3.5 Silberschatz, Galvin and Gagne ©2009
Process in Memory Operating System Concepts – 8th Edition 3.6 Silberschatz, Galvin and Gagne ©2009
Process State s As a process executes, it changes state q new: The process is being created q running: Instructions are being executed q waiting: The process is waiting for some event to occur q ready: The process is waiting to be assigned to a processor q terminated: The process has finished execution Operating System Concepts – 8th Edition 3.7 Silberschatz, Galvin and Gagne ©2009
Diagram of Process State Operating System Concepts – 8th Edition 3.8 Silberschatz, Galvin and Gagne ©2009
Process Control Block (PCB) Information associated with each process s Process state s Program counter s CPU registers s CPU scheduling information s Memory-management information s Accounting information s I/O status information Operating System Concepts – 8th Edition 3.9 Silberschatz, Galvin and Gagne ©2009
Process Control Block (PCB) Operating System Concepts – 8th Edition 3.10 Silberschatz, Galvin and Gagne ©2009
CPU Switch From Process to Process Operating System Concepts – 8th Edition 3.11 Silberschatz, Galvin and Gagne ©2009
Process Scheduling s Maximize CPU use, quickly switch processes onto CPU for time sharing s Process scheduler selects among available processes for next execution on CPU s Maintains scheduling queues of processes q Job queue – set of all processes in the system q Ready queue – set of all processes residing in main memory, ready and waiting to execute q Device queues – set of processes waiting for an I/O device q Processes migrate among the various queues Operating System Concepts – 8th Edition 3.12 Silberschatz, Galvin and Gagne ©2009
Process Representation in Linux s Represented by the C structure task_struct pid t pid; /* process identifier */ long state; /* state of the process */ unsigned int time slice /* scheduling information */ struct task struct *parent; /* this process’s parent */ struct list head children; /* this process’s children */ struct files struct *files; /* list of open files */ struct mm struct *mm; /* address space of this pro */ Operating System Concepts – 8th Edition 3.13 Silberschatz, Galvin and Gagne ©2009
Ready Queue And Various I/O Device Queues Operating System Concepts – 8th Edition 3.14 Silberschatz, Galvin and Gagne ©2009
Representation of Process Scheduling Operating System Concepts – 8th Edition 3.15 Silberschatz, Galvin and Gagne ©2009
Schedulers s Long-term scheduler (or job scheduler) – selects which processes should be brought into the ready queue s Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU q Sometimes the only scheduler in a system Operating System Concepts – 8th Edition 3.16 Silberschatz, Galvin and Gagne ©2009
Schedulers (Cont.) s Short-term scheduler is invoked very frequently (milliseconds) (must be fast) s Long-term scheduler is invoked very infrequently (seconds, minutes) (may be slow) s The long-term scheduler controls the degree of multiprogramming s Processes can be described as either: q I/O-bound process – spends more time doing I/O than computations, many short CPU bursts q CPU-bound process – spends more time doing computations; few very long CPU bursts Operating System Concepts – 8th Edition 3.17 Silberschatz, Galvin and Gagne ©2009
Addition of Medium Term Scheduling Operating System Concepts – 8th Edition 3.18 Silberschatz, Galvin and Gagne ©2009
Context Switch s 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. s Context of a process represented in the PCB s Context-switch time is overhead; the system does no useful work while switching q The more complex the OS and the PCB -> longer the context switch s Time dependent on hardware support q Some hardware provides multiple sets of registers per CPU -> multiple contexts loaded at once Operating System Concepts – 8th Edition 3.19 Silberschatz, Galvin and Gagne ©2009
Process Creation s Parent process create children processes, which, in turn create other processes, forming a tree of processes s Generally, process identified and managed via a process identifier (pid) s Resource sharing q Parent and children share all resources q Children share subset of parent’s resources q Parent and child share no resources s Execution q Parent and children execute concurrently q Parent waits until children terminate Operating System Concepts – 8th Edition 3.20 Silberschatz, Galvin and Gagne ©2009