3. Process Concept in operating system.pptx

3. Process Concept in operating system.pptx

1. Operating System Process Management Dr. Manish Bansal

2. Processes Process Concept Process Scheduling Operation on Processes Cooperating Processes Inter process communication

3. Process Concept A process is a program in execution For example, when we write a program in C or C++ and compile it, the compiler creates binary code. The original code and binary code are both programs. When we actually run the binary code, it becomes a process. A process is an ‘active’ entity, as opposed to a program, which is considered to be a ‘passive’ entity. A single program can create many processes when run multiple times; for example, when we open “a .exe” or binary file multiple times, multiple instances begin (multiple processes are created). A process includes: Program counter – Specifies address of next instruction to be executed Stack – It includes temporary data like method parameters, return address and local variables Data section- It includes global variables

4. 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.

5. Diagram of Process State

6. 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

7. PCB Cont… Process State: new, ready, running, waiting, halted Program Counter: It stores address of next instruction to be executed CPU registers: accumulators, index register, stack pointer and condition code information CPU scheduling information: it includes process priority, pointers to scheduling queues etc. Memory-Management Information: it includes value of base register and limit registers, info of page table and segmentation tables etc. Accounting information: it includes CPU time used, process number (PID). I/O status information: The information includes the list of I/O devices allocated to this process, list of open files and so on.

8. Process Control Block (PCB)

9. Thread Thread is a Single Process which a program executes at one time Most of the Program can execute only one thread at a time In Latest technologies a multithreaded based system has been evolved In Multi thread system Operating system can execute multiple threads on time sharing basis.

10. Operating System Process Management Dr. Manish Bansal

11. Processes Process Scheduling Operation on Processes Cooperating Processes Inter process communication

12. 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. Process migration between the various queues.

13. Ready Queue And Various I/O Device Queues

14. Representation of Process Scheduling

15. Schedulers Long-term Scheduler (or job scheduler) – It is also called a job  scheduler . A  long - term scheduler  determines which programs are admitted to the system for processing. It selects processes from the queue and loads them into memory for execution. Process loads into the memory for CPU  scheduling .. Short-term Scheduler (or CPU scheduler) The  short - term scheduler  (also known as the CPU  scheduler ) decides which of the ready, in-memory processes is to be executed (allocated a CPU) after a clock interrupt, an I/O interrupt, an operating system call or another form of signal

16. Addition of Medium Term Scheduling

17. 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.

18. 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. Context-switch time is overhead; the system does no useful work while switching. Time dependent on hardware support.

19. Operating System Process Management Dr. Manish Bansal

20. Processes Operation on Processes Cooperating Processes Inter process communication

21. Operation on process Process Creation Parent process creates children processes, which, in turn create other processes, forming a tree of processes. There is Unique Identifier for each Process (PID) Resource sharing Parent and children share all resources. Children share subset of parent’s resources. Execution Parent and children execute concurrently. Parent waits until children terminate.

22. Address space Child duplicate of parent. Child has a program loaded into it. Operation on process Process Creation Cont…

23. A Tree of Processes On A Typical UNIX System

24. Process Termination Process executes last statement and asks the operating system to decide it ( exit ). Output data from child to parent (via wait ). Process’ resources are deallocated by operating system. Parent may terminate execution of children processes ( abort ). Child has exceeded allocated resources. Task assigned to child is no longer required. Parent is exiting. Operating system does not allow child to continue if its parent terminates. This is called cascading termination.

25. Producer Consumer problem To illustrate the concept of cooperating processes, let us consider the producer-consumer problem . The producer process produces information that is consumed by the consumer process. E.g. a printer program produces characters that are consumed by printer To allow processor and consumer processes to run concurrently, we must have available a buffer of items that can be filled by producer and emptied by consumer.

26. Producer Consumer problem To synchronies producer and consumer, consumer should consume item only if it is produced by producer. Buffer Types Unbounded Buffer:- Producer consumer problem places no practical limit on the size of the buffer. Bounded Buffer:- Producer consumer problem assume a fixed size buffer. In this case, the consumer must wait if the buffer is empty, and the producer must wait if the buffer is full

27. Producer Consumer problem Lets discuss shared memory solution to the bounder-buffer problem The shared buffer will be implemented as a circular array with two logical pointers: in (points to the next free position in buffer) and out (points to the first position in the buffer). The buffer is empty when in == out ; and buffer is full when ((in+1) % BUFFER_SIZE)==out

28. Producer Consumer problem Code for Producer process

29. Producer consumer problem

30. Producer Consumer problem Code for Consumer Process

31. Producer consumer problem

32. Interprocess Communication The concurrent processes executing in the operating system may be either independent processes or cooperating processes. Independent:- A process is independent means that does not share any data with any other process is independent. Cooperating :- The process is cooperating if any process shares data with other processes is a cooperating process.

33. Cooperating Processes The system should provide an environment that allows process cooperating for several reasons. Information Sharing:- Several users may be interested to share same information so the system must provide an environment to allow concurrent access to these types of recourses . Computation speedup :- A task should be broken into subtasks, each of which will be executing in parallel with the others. Such a speed up can be achieved only if the computer has multiple processing elements. Modularity:- System should be constructed in modular (processes or threads) fashion. Convenience:- System should be such that individual user can work on multiple tasks like editing, printing and compiling etc.

34. Inter-process communication (IPC) There are two models of Inter Process Communication Direct Communication or Message Passing Indirect Communication or Shared Memory

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36. Message Passing Message passing is useful when small amount of data is required to be exchanged It is easier to implement as compared to Share Memory It require system call through Kernal intervention Processes must name each other explicitly: send (P, message) – send a message to process P receive(Q, message) – receive a message from process Q Properties of communication link Links are established automatically. A link is associated with exactly one pair of communicating processes. Between each pair there exists exactly one link. The link may be unidirectional, but is usually bi-directional

37. Shared Memory Shared memory allows maximum speed Shared memory is faster than message passing In this all the process establish a region of common shared memory A shared memory is generally is part of address space of e parent process which is creating the shared memory space. All other cooperating process share the same address space Any process which requires to share the information between cooperating process shares the information in shared memory.

38. Indirect communication Operations create a new mailbox send and receive messages through mailbox destroy a mailbox Primitives are defined as: send(A, message) – send a message to mailbox A receive(A, message) – receive a message from mailbox A

39. Indirect Communication Mailbox sharing P1, P2, and P3 share mailbox A. P1, sends; P2 and P3 receive. Who gets the message? Solutions Allow a link to be associated with at most two processes. Allow only one process at a time to execute a receive operation. Allow the system to select arbitrarily the receiver. Sender is notified who the receiver was.

40. Synchronization Message passing may be either blocking or non-blocking. Blocking is considered synchronous . Non-blocking is considered asynchronous Blocking Send: The sending process is blocked until the msg is received by the receiving process Nonblocking send: The sending process sends the msg and resumes operation. Blocking receive: The receiver blocks until a msg is available Nonblocking receive: The receiver retrieves either a valid msg or a null.

41. Buffering Queue of messages attached to the link; implemented in one of three ways. Zero capacity – 0 messages Sender must wait for receiver (rendezvous). 2. Bounded capacity – finite length of n messages Sender must wait if link full. 3. Unbounded capacity – infinite length. Sender never waits.