CS 134: Operating Systems

Transcription

1 CS 134: Operating Systems CS 134: Operating Systems 1 / 25

2 Overview Overview Overview in Unix Implementation States Concepts Uses Design in Unix Implementation States Concepts Uses Design 2 / 25

3 3 / 25 & Concurrency & Concurrency & Concurrency What is a process? What is concurrency? What is a process? What is concurrency?

4 4 / 25 s View of s View of s View of A fundamental OS abstraction But details vary from OS to OS: Batch system Jobs Time-shared systems programs or tasks Common idea: Process = A program in execution have a degree of independence from each other Possibly only allowed communicate through designated mechanisms One errant processes should not affect other unrelated ones A fundamental OS abstraction But details vary from OS to OS: Batch system Jobs Time-shared systems programs or tasks Common idea: Process = A program in execution have a degree of independence from each other Possibly only allowed communicate through designated mechanisms One errant processes should not affect other unrelated ones

5 Class Exercise Class Exercise Class Exercise What makes up a process? ( A process has... ) In general On a typical POSIX system What makes up a process? ( A process has... ) In general On a typical POSIX system 5 / 25

6 6 / 25 in Unix Components of a Process (Unix) Execution state I/O State Registers File descriptors Program counter Working directory Program status word Root directory pointer Event Notifications Scheduling information Signals waiting Process state Signal mask Priority Time of next alarm Class, etc. Other Memory Process ID Text area Parent process Data area Process group area Controlling terminal Security/Authentication Info Start time ID CPU time Group ID Children s CPU time in Unix Components of a Process (Unix) Components of a Process (Unix) Execution state Registers Program counter Program status word pointer Scheduling information Process state Priority Class, etc. Memory Text area Data area area Security/Authentication Info ID Group ID I/O State File descriptors Working directory Root directory Event Notifications Signals waiting Signal mask Time of next alarm Other Process ID Parent process Process group Controlling terminal Start time CPU time Children s CPU time

7 in Unix under UNIX in Unix under UNIX under UNIX : Create with fork Exit with exit Replace process image with execve Multiple processes may be active at any one time (compare w/ uniprogrammed system) : Create with fork Exit with exit Replace process image with execve Multiple processes may be active at any one time (compare w/ uniprogrammed system) 7 / 25

8 8 / 25 Class Question in Unix in Unix Class Question Class Question If there s fork, should we have join? If there s fork, should we have join?

9 in Unix 9 / 25 coreservicesd diskarbitrationd ATSServer SystemStarter SecurityServer dynamic_pager distnoted automount mach_init rpc.lockd syslogd update cupsd ntpd lookupd notifyd configd root init nfsiod automount kextd netinfod mdnsresponder cron DirectoryService xinetd EventAgent crashreporterd loginwindow TabletDriverRelauncher TabletDriver nobody AppleSpell pbs WindowServer TextEdit Safari Dock p2 SystemUIServer Finder System Preview Keynote MouseWorks UniversalAccess ssh -tcsh login melissa TeXShop Terminal -tcsh login -tcsh man login p5 login sh login login -tcsh p1 sh ps p4 less -tcsh p6 -tcsh p3 under UNIX The environment you interact with is made up of processes in Unix under UNIX under UNIX The environment you interact with is made up of processes nobody lookupd mdnsresponder distnoted configd DirectoryService coreservicesd mach_init EventAgent diskarbitrationd automount ATSServer rpc.lockd crashreporterd cron SystemStarter syslogd root loginwindow xinetd update SecurityServer init TabletDriverRelauncher dynamic_pager cupsd nfsiod TabletDriver automount ntpd kextd notifyd netinfod p2 SystemUIServer AppleSpell Safari pbs WindowServer Dock TextEdit ssh man p1 -tcsh -tcsh sh less login Finder login sh p4 System melissa login -tcsh Preview Terminal login -tcsh Keynote TeXShop login ps p3 MouseWorks login -tcsh p6 UniversalAccess -tcsh p5

10 Implementation 10 / 25 Process Implementation Implementation Process Implementation Process Implementation How does the OS implement the process abstraction? How does the OS implement the process abstraction?

11 11 / 25 Implementation Process Implementation (cont d) Implementation Process Implementation (cont d) Process Implementation (cont d) The OS needs to maintain a process image for each process: Process s address space, containing: Program code Program data Processor stack Housekeeping information (PCB) One of most important is process state The OS needs to maintain a process image for each process: Process s address space, containing: Program code Program data Processor stack Housekeeping information (PCB) One of most important is process state

12 12 / 25 A Two-State Process Model States States A Two-State Process Model A Two-State Process Model Simplest model for processes: Not Running Running Simplest model for processes: Not Running Running

13 13 / 25 States A Four-State Process Model More useful model for processes: States A Four-State Process Model A Four-State Process Model More useful model for processes: Ready Running Blocked Finished Ready Running Finished Blocked

14 States New Ready Blocked Running Finished A Five-State Process Model Five states can model additional needs of batch systems: States A Five-State Process Model A Five-State Process Model Five states can model additional needs of batch systems: Scheduler queues: Ready queue: ready and waiting to execute. New queue: waiting to be created New Ready Running Finished Blocked Scheduler queues: Ready queue: ready and waiting to execute. New queue: waiting to be created 14 / 25

15 Concepts Generalizing Concepts Generalizing Generalizing Simple view of process is Address space + Thread of execution Does the mapping need to be one-to-one? Simple view of process is Address space + Thread of execution Does the mapping need to be one-to-one? 15 / 25

16 16 / 25 Possible Mappings Concepts Concepts Possible Mappings Possible Mappings one process one thread multiple processes one thread per process one process multiple threads multiple processes multiple threads per process one process one thread one process multiple threads multiple processes one thread per process multiple processes multiple threads per process

17 Concepts Concepts Motivation: Traditional processes: Virtual uniprocessor machine Multithreaded processes: Virtual multiprocessor machine Motivation: Traditional processes: Virtual uniprocessor machine Multithreaded processes: Virtual multiprocessor machine 17 / 25

18 Uses Uses of Uses Uses of Uses of Various reasons why people use threads Performing foreground and background work Supporting asynchronous processing Speeding execution Organizing programs Various reasons why people use threads Performing foreground and background work Supporting asynchronous processing Speeding execution Organizing programs 18 / 25

19 Uses Dispatcher thread Network connection Web server process Worker thread Web page cache space space Uses of Example Web server process Uses Uses of Example Uses of Example /* Dispatcher Thread */ for ( ; ; ) { url = get_next_request(); handoff_work(url); } /* Worker Thread */ \\ for ( ; ; ) { url = wait_for_work(); page = look_in_cache(url); if (page == NULL) page = generate_page(url); send_page(page); } Dispatcher thread Worker thread space Web page cache space Network connection /* Dispatcher Thread */ for ( ; ; ) { url = get_next_request(); handoff_work(url); } /* Worker Thread */ \\ for ( ; ; ) { url = wait_for_work(); page = look_in_cache(url); if (page == NULL) page = generate_page(url); send_page(page); } 19 / 25

20 Uses Class Exercise Uses Class Exercise Class Exercise Can an application implement threads without built-in thread support in the OS? If so, what does it need from the from the OS to support threads? Can an application implement threads without built-in thread support in the OS? If so, what does it need from the from the OS to support threads? 20 / 25

21 21 / 25 Library Model for Model for Model for Key: -level thread -level thread P Process P Pure user-level Class Exercise What are the pros and cons of this approach? Library P Key: -level thread -level thread P Process So, maybe we should put the threads in the kernel? Pure user-level Class Exercise What are the pros and cons of this approach?

22 Library Model for Model for Model for Key: -level thread -level thread P Process P Pure user-level + No kernel overhead for thread library calls + Own scheduler = Application-specific scheduling policy? I/O issues Can t (easily) take advantage of multiprocessing Library P Key: -level thread -level thread P Process So, maybe we should put the threads in the kernel? Pure user-level + No kernel overhead for thread library calls + Own scheduler = Application-specific scheduling policy? I/O issues Can t (easily) take advantage of multiprocessing 21 / 25

23 22 / 25 P Pure kernel-level -level thread P Process Model for -Level Model for -Level Model for -Level Key: Class Exercise What are the pros and cons of this approach? -level thread P Pure kernel-level Key: -level thread -level thread P Process Class Exercise What are the pros and cons of this approach?

24 22 / 25 P Pure kernel-level -level thread P Process Model for -Level Model for -Level Model for -Level Now we have kernel overheads: data structures Mode switch to kernel Key: -level thread P Pure kernel-level Key: -level thread -level thread P Process Now we have kernel overheads: data structures Mode switch to kernel

25 23 / 25 Library Hybrid Thread Schemes Hybrid Thread Schemes Hybrid Thread Schemes P P Combined Key: -level thread -level thread P Process Class Exercise What are the pros and cons of this approach? P Library P Key: -level thread -level thread P Process Combined Class Exercise What are the pros and cons of this approach?

26 24 / 25 Traditional vs. Multithreaded Single-Threaded Process Model Traditional vs. Multithreaded Traditional vs. Multithreaded Single-Threaded Process Model Process Control Block Address Process Control Block Address

27 24 / 25 Process Control Block Address Thread Thread Control Block Thread Thread Control Block Thread Thread Control Block Traditional vs. Multithreaded Single-Threaded Process Model Process Control Block Address Process Control Block Address Multithreaded Process Model Thread Thread Thread Control Block Thread Control Block Thread Thread Control Block Traditional vs. Multithreaded Traditional vs. Multithreaded Single-Threaded Multithreaded Process Model Process Model Process Control Block Address Class Question But what s per-process and what s per-thread? Class Question But what s per-process and what s per-thread?

28 25 / 25 Design Per-Process vs. Per-Thread You Decide... Execution state Registers Program counter Program status word pointer Scheduling information Process state Priority Class, etc. Memory Text area Data area area Security/Authentication Info ID Group ID I/O State File descriptors Working directory Root directory Event Notifications Signals waiting Signal mask Time of next alarm Other Process ID Parent process Process group Controlling terminal Start time CPU time Children s CPU time Design Per-Process vs. Per-Thread You Decide... Per-Process vs. Per-Thread You Decide... Execution state Registers Program counter Program status word pointer Scheduling information Process state Priority Class, etc. Memory Text area Data area area Security/Authentication Info ID Group ID I/O State File descriptors Working directory Root directory Event Notifications Signals waiting Signal mask Time of next alarm Other Process ID Parent process Process group Controlling terminal Start time CPU time Children s CPU time