Operating systems. Module 7 IPC (Interprocess communication) PART I. Tami Sorgente 1

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1 Operating systems Mdule 7 IPC (Interprcess cmmunicatin) PART I Tami Srgente 1

2 INTERPROCESS COMMUNICATION Prcesses within a system may be independent r cperating Cperating prcess can affect r be affected by ther prcesses, including sharing data Reasns fr cperating prcesses: Infrmatin sharing Cmputatin speedup Mdularity Cnvenience Tw mdels f IPC Shared memry Message passing Tami Srgente 2

3 COMMUNICATION MODELS (a) message passing (b) shared memry Tami Srgente 3

4 PRODUCER-CONSUMER PROBLEM Paradigm fr cperating prcesses, prducer prcess prduces infrmatin that is cnsumed by a cnsumer prcess unbunded-buffer places n practical limit n the size f the buffer bunded-buffer assumes that there is a fixed buffer size Tami Srgente 4

5 IPC MESSAGE PASSING Mechanism fr prcesses t cmmunicate and t synchrnize their actins Message system prcesses cmmunicate with each ther withut resrting t shared variables IPC facility prvides tw peratins: send(message) message size fixed r variable receive(message) If P and Q wish t cmmunicate, they need t: establish a cmmunicatin link between them exchange messages via send/receive Implementatin f cmmunicatin link physical (e.g., shared memry, hardware bus) lgical (e.g., direct r indirect, synchrnus r asynchrnus) Tami Srgente 5

6 IPC MESSAGE PASSING Implementatin Questins Hw are links established? Can a link be assciated with mre than tw prcesses? Hw many links can there be between every pair f cmmunicating prcesses? What is the capacity f a link? Is the size f a message that the link can accmmdate fixed r variable? Is a link unidirectinal r bi-directinal? Tami Srgente 6

7 DIRECT COMMUNICATION Prcesses must name each ther explicitly: send (P, message) send a message t prcess P receive(q, message) receive a message frm prcess Q Prperties f direct cmmunicatin link A link is assciated with exactly ne pair f cmmunicating prcesses Between each pair there exists exactly ne link The link may be unidirectinal, but is usually bidirectinal Tami Srgente 7

INDIRECT COMMUNICATION Messages are directed and received frm mailbxes (als referred t as prts) Each mailbx has a unique id Prcesses can cmmunicate nly if they share a mailbx Prperties f cmmunicatin

8 INDIRECT COMMUNICATION Messages are directed and received frm mailbxes (als referred t as prts) Each mailbx has a unique id Prcesses can cmmunicate nly if they share a mailbx Prperties f cmmunicatin link Link established nly if prcesses share a cmmn mailbx A link may be assciated with many prcesses Each pair f prcesses may share several cmmunicatin links Link may be unidirectinal r bi-directinal Tami Srgente 8

9 MESSAGE SYNCHRONIZATION Message passing may be either blcking r nnblcking Blcking is cnsidered synchrnus Blcking send has the sender blck until the message is received Blcking receive has the receiver blck until a message is available Nn-blcking is cnsidered asynchrnus Nn-blcking send has the sender send the message and cntinue Nn-blcking receive has the receiver receive a valid message r null Tami Srgente 9

10 BUFFERING Queue f messages attached t the link; implemented in ne f three ways 1. Zer capacity 0 messages Sender must wait fr receiver (rendezvus) 2. Bunded capacity finite length f n messages Sender must wait if link full 3. Unbunded capacity infinite length Sender never waits Tami Srgente 10

11 Operating systems Mdule 7 Thread Cncept PART II Tami Srgente 11

12 THREADS Overview Multicre Prgramming Multithreading Mdels Thread Libraries Implicit Threading Thread Cancellatin Tami Srgente 12

13 THREADS - OVERVIEW What is a thread? A lightweight prcess A unit f executin f a prcess Tami Srgente 13

14 THREADS - OVERVIEW single threaded and multithreaded Tami Srgente 14

15 THREADS - OVERVIEW Mst mdern applicatins are multithreaded Multiple tasks can be implemented by separate threads Update display Fetch data Spell checking Answer a netwrk request Prcess creatin is heavy-weight while thread creatin is light-weight Kernels are generally multithreaded Tami Srgente 15

16 BENEFITS OF THREADS Respnsiveness may allw cntinued executin if part f prcess is blcked, especially imprtant fr user interfaces Resurce Sharing threads share resurces f prcess Ecnmy cheaper than prcess creatin, thread switching lwer verhead than cntext switching Scalability prcess can take advantage f multiprcessr architectures Tami Srgente 16

17 MULTICORE PROGRAMMING Multicre r multiprcessr systems putting pressure n prgrammers, challenges include: Dividing activities Balance Data splitting Data dependency Testing and debugging Parallelism implies a system can perfrm mre than ne task simultaneusly Cncurrency supprts mre than ne task making prgress Single prcessr / cre, scheduler prviding cncurrency Tami Srgente 17

18 CONCURRENCY VS. PARALLELISM Cncurrent executin n single-cre system: Parallelism n a multi-cre system: Tami Srgente 18

19 USER THREADS AND KERNEL THREADS User threads - management dne by user-level threads library Three primary thread libraries: POSIX Pthreads Win32 threads Java threads Kernel threads - Supprted by the Kernel Examples virtually all general purpse perating systems, including: Windws Slaris Linux Tru64 UNIX Mac OS X Tami Srgente 19

20 MULTITHREADING MODELS Many-t-One One-t-One Many-t-Many Tw- level Tami Srgente 20

21 MANY-TO-ONE Many user-level threads mapped t single kernel thread One thread blcking causes all t blck Multiple threads may nt run in parallel n muticre system because nly ne may be in kernel at a time Few systems currently use this mdel Tami Srgente 21

22 ONE-TO-ONE Each user-level thread maps t kernel thread Creating a user-level thread creates a kernel thread Mre cncurrency Number f threads per prcess smetimes restricted due t verhead Tami Srgente 22

23 MANY-TO-MANY MODEL Allws many user level threads t be mapped t many kernel threads Allws the perating system t create a sufficient number f kernel threads Tami Srgente 23

24 TWO-LEVEL MODEL Similar t M:M, except that it allws a user thread t be bund t kernel thread Tami Srgente 24

25 THREAD LIBRARIES Thread library prvides prgrammer with API fr creating and managing threads Tw primary ways f implementing Library entirely in user space Kernel-level library supprted by the OS Tami Srgente 25

26 IMPLICIT THREADING Grwing in ppularity as numbers f threads increase, prgram crrectness mre difficult with explicit threads Creatin and management f threads dne by cmpilers and run-time libraries rather than prgrammers Three methds explred Thread Pls OpenMP Grand Central Dispatch Other methds include Micrsft Threading Building Blcks (TBB), java.util.cncurrent package Tami Srgente 26

27 THREAD POOLS Create a number f threads in a pl where they await wrk Advantages: Usually slightly faster t service a request with an existing thread than create a new thread Allws the number f threads in the applicatin(s) t be bund t the size f the pl Separating task t be perfrmed frm mechanics f creating task allws different strategies fr running task Tami Srgente 27

28 OPENMP Set f cmpiler directives and an API fr C, C++, FORTRAN Prvides supprt fr parallel prgramming in sharedmemry envirnments Identifies parallel regins blcks f cde that can run in parallel #pragma mp parallel Create as many threads as there are cres #pragma mp parallel fr fr(i=0;i<n;i++) { c[i] = a[i] + b[i]; } Run fr lp in parallel Tami Srgente 28

29 GRAND CENTRAL DISPATCH Apple technlgy fr Mac OS X and ios perating systems Extensins t C, C++ languages, API, and run-time library Allws identificatin f parallel sectins Manages mst f the details f threading Blcks placed in dispatch queue Assigned t available thread in thread pl when remved frm queue Tami Srgente 29

30 THREAD CANCELLATION Terminating a thread befre it has finished Thread t be canceled is target thread Tw general appraches: Asynchrnus cancellatin terminates the target thread immediately Deferred cancellatin allws the target thread t peridically check if it shuld be cancelled Tami Srgente 30

CS4500/5500 Operating Systems Synchronization

CS4500/5500 Operating Systems Synchronization Operating Systems Synchrnizatin Yanyan Zhuang Department f Cmputer Science http://www.cs.uccs.edu/~yzhuang UC. Clrad Springs Recap f the Last Class Multiprcessr scheduling Tw implementatins f the ready