L-5 BCEProcess management.ppt
0 likes49 views
The document discusses key concepts related to process management in operating systems. It describes that an OS executes programs as processes, which can be in various states like running, waiting, ready etc. It also explains process control blocks that contain details of a process like state, registers, scheduling info etc. The document discusses process scheduling and synchronization techniques used by the OS to share CPU and other resources between multiple processes. It describes mechanisms for process creation, termination and interprocess communication using shared memory and message passing.
L-5 BCEProcess management.ppt
- 2. Process State Process Control Block Operations on Processes Process Scheduling Process Synchronisation Interprocess Communication
- 3. An operating system executes a variety of programs: Batch system – jobs Time-shared systems – user programs or tasks Process – a program in execution; process execution must progress in sequential fashion CPU executes a single process at a time instance. Process related terminology Process code : set of instruction at a time instance. Process associated data Process Components: Resources required for execution. Process state
- 4. 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
- 6. Information associated with each process (also called task control block) Process state – running, waiting, etc Program counter – location of instruction to next execute CPU registers – contents of all process- centric registers CPU scheduling information- priorities, scheduling queue pointers Memory-management information – memory allocated to the process Accounting information – CPU used, clock time elapsed since start, time limits I/O status information – I/O devices allocated to process, list of open files
- 7. 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 ◦ Processes migrate among the various queues
- 8. Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU. READY RUNNING Long-term Scheduler (or job scheduler) – selects which processes should be brought into the ready queue. NEW READY RUNNING TERMINATING Mid-Term Scheduler-Moves process from main memory to secondary memory during waiting state and vice versa RUNNING WAITING WAITING READY
- 9. System must provide mechanisms for: ◦ process creation, ◦ process termination, ◦ and so on as detailed next
- 10. Parent process create children processes, which, in turn create other processes, forming a tree of processes Generally, process identified and managed via a process identifier (pid) Resource sharing options ◦ Parent and children share all resources ◦ Children share subset of parent’s resources ◦ Parent and child share no resources Execution options ◦ Parent and children execute concurrently ◦ Parent waits until children terminate
- 11. init pid = 1 sshd pid = 3028 login pid = 8415 kthreadd pid = 2 sshd pid = 3610 pdflush pid = 200 khelper pid = 6 tcsch pid = 4005 emacs pid = 9204 bash pid = 8416 ps pid = 9298
- 12. Processes within a system may be independent or cooperating Cooperating process can affect or be affected by other processes, including sharing data Reasons for cooperating processes: ◦ Information sharing ◦ Computation speedup ◦ Modularity ◦ Convenience Cooperating processes need interprocess communication (IPC) Two models of IPC ◦ Shared memory ◦ Message passing
- 13. (a) Message passing. (b) shared memory.
- 14. Multiple process wait for each other to free up resources and all the process remains in halt (waiting state)