操作系统概念(第七版_英文版)ch3.ppt

Chapter 3: Processes Chapter 3: Processes Process Concept Process Scheduling Operations on Processes Cooperating Processes Interprocess Communication Communication in Client-Server Systems 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 heap Process in Memory 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 Diagram of Process State 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 Process Control Block (PCB) CPU Switch From Process to Process Process Scheduling Queues 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 Processes migrate among the various queues Ready Queue And Various I/O Device Queues Representation of Process Scheduling 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 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 e