Chapter 3Process Description and Control课件.ppt

Two-State Process Model To control processes, we need to describe their behavior Process may be in one of two states Running Not-running 精品文档 Queuing Diagram Etc … processes moved by the dispatcher of the OS to the CPU then back to the queue until the task is competed Processes that are not running must be kept in some sort of queue, waiting their turn to execute. 精品文档 Process Birth and DeathCommon Reasons Creation Termination New batch job Normal Completion Interactive Login Memory unavailable Created by OS to provide a service Protection error Spawned by existing process Operator or OS Intervention See tables 3.1 and 3.2 for more 精品文档 Process Creation The OS builds a data structure to manage the process Traditionally, the OS creates all processes But it can be useful to let a running process create another, e.g., a server process may generate a new process for each request This action is called process spawning Parent Process is the original, creating process Child Process is the new process 精品文档 Process Termination There must be some way that a process can indicate completion. This indication may be: A HALT instruction for termination in a batch job A user action (e.g. log off, quitting an application) A fault or error Parent process terminating 精品文档 Five-State Process Model Processes may be blocked (e.g., waiting for an I/O operation) 精品文档 Using Two Queues 精品文档 Multiple Blocked Queues 精品文档 Suspended Processes Processor is faster than I/O, so all processes could be waiting for I/O Swap these processes to disk to free up more memory and use processor on more processes Blocked state becomes suspend state when swapped to disk 精品文档 One Suspend State 精品文档 Two Suspend States When the event of a suspended (and blocked) process occurs, the process is not blocked and is potentially available for execution. 精品文档 Process SuspensionCommon Reasons Reason Comment Swapping The OS needs to release sufficient main memory to bring in a process that is ready to execute. O