1. Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition, Chapter 3: Processes

2. 3.2 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Chapter 3: Processes Process Concept Process Scheduling Operations on Processes Interprocess Communication Examples of IPC Systems Communication in Client-Server Systems

3. 3.3 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition 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

4. 3.4 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Process in Memory

5. 3.5 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition 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

6. 3.6 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Diagram of Process State

7. 3.7 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition 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

8. 3.8 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition 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

9. 3.9 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Ready Queue And Various I/O Device Queues

10. 3.10 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Representation of Process Scheduling

11. 3.11 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition 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

12. 3.12 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition 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

13. 3.13 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Addition of Medium Term Scheduling

14. 3.14 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition 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 via a context switch Context of a process represented in the PCB Context-switch time is overhead; the system does no useful work while switching Time dependent on hardware support

15. 3.15 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Process Creation 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 Parent and children share all resources Children share subset of parent’s resources Parent and child share no resources Execution Parent and children execute concurrently Parent waits until children terminate

16. 3.16 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Process Creation (Cont) Address space Child duplicate of parent Child has a program loaded into it UNIX examples fork system call creates new process exec system call used after a fork to replace the process’ memory space with a new program

17. 3.17 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition C Program Forking Separate Process int main() { pid_t pid; /* fork another process */ pid = fork(); if (pid < 0) { /* error occurred */ fprintf(stderr, "Fork Failed"); exit(-1); } else if (pid == 0) { /* child process */ execlp("/bin/ls", "ls", NULL); } else { /* parent process */ /* parent will wait for the child to complete */ wait (NULL); printf ("Child Complete"); exit(0); }

18. 3.18 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Process Termination Process executes last statement and asks the operating system to delete 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 If parent is exiting  Some operating system do not allow child to continue if its parent terminates – All children terminated - cascading termination

19. 3.19 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Interprocess Communication 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

20. 3.20 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Communications Models

21. 3.21 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Single and Multithreaded Processes

22. 3.22 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Benefits Responsiveness Resource Sharing Economy Scalability

23. 3.23 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Multicore Programming Multicore systems putting pressure on programmers, challenges include Dividing activities Balance Data splitting Data dependency Testing and debugging

24. 3.24 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Thread Libraries Thread library provides programmer with API for creating and managing threads Two primary ways of implementing Library entirely in user space Kernel-level library supported by the OS

25. 3.25 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition User Threads Thread management done by user-level threads library Three primary thread libraries: POSIX Pthreads Win32 threads Java threads

26. 3.26 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Pthreads May be provided either as user-level or kernel-level A POSIX standard (IEEE 1003.1c) API for thread creation and synchronization API specifies behavior of the thread library, implementation is up to development of the library Common in UNIX operating systems (Solaris, Linux, Mac OS X)

27. 3.27 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Java Threads Java threads are managed by the JVM Typically implemented using the threads model provided by underlying OS Java threads may be created by: Extending Thread class Implementing the Runnable interface

28. 3.28 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Threading Issues Semantics of fork() and exec() system calls Thread cancellation of target thread Asynchronous or deferred Signal handling Thread pools Thread-specific data Scheduler activations

29. 3.29 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Semantics of fork() and exec() Does fork() duplicate only the calling thread or all threads?

30. 3.30 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Signal Handling Signals are used in UNIX systems to notify a process that a particular event has occurred A signal handler is used to process signals  Signal is generated by particular event  Signal is delivered to a process  Signal is handled Options: Deliver the signal to the thread to which the signal applies Deliver the signal to every thread in the process Deliver the signal to certain threads in the process Assign a specific threa to receive all signals for the process

31. 3.31 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Thread Pools Create a number of threads in a pool where they await work Advantages: Usually slightly faster to service a request with an existing thread than create a new thread Allows the number of threads in the application(s) to be bound to the size of the pool

32. 3.32 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Linux Threads Linux refers to them as tasks rather than threads Thread creation is done through clone() system call clone() allows a child task to share the address space of the parent task (process)

33. 3.33 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition Linux Threads