Pthreads Programming

8/12/2019 Pthreads Programming

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Pthreads Programming: A

Hands-on Introduction

Adrien Lamothe

[email protected]

Monday, July 23, 2007

8:30 am !2:00 noon

"oom #!3$%!&0Copyright 2007 Adrien LamotheAll Rights Resered
mailto:[email protected]:[email protected]


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Agenda

We're going to cover fundamental concepts of multi-threaded

programming and Pthreads. We'll play around with some simple C

programs, that utilize Pthreads, to learn the basics and to illustrate

some important concepts. Due to time limitation, we may not be able

to tal about some of the finer points of Pthreads programming.

!his is not a comprehensive tutorial. !he goal is to get you "uicly

familiar with multi-threaded programming concepts and Pthreadsprogramming. #f you haven't wored with threads before, this tutorial

should serve as a good starting point. #f you are more e$perienced, you

may or may not benefit from this tutorial% there will be some discussion

that may interest those of you with nowledge and e$perience of the

topic.

!his set of slides will serve as our guide. &nce we get to the e$ample

programs the activity will also involve actually running and changing

the programs, in order to have some fun and see first-hand how

Pthreads actually wor.


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Background

Concurrent systems and multi-threadedprogramming have been with us a number of

years.

ecent developments (clusters, multi-coremicroprocessors) have led to renewed interest in

concurrent programming.


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New Multicore Processors

*un +icrosystems iagara / cores#0+ Cell 0roadband 1ngine (C01) up to 2 coresParalla$ Propeller Chip 3 cores#ntel Core / Duo, 4uad Core / and 5 cores

6+D Dual Core (soon to release "uad core)


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Background

#n the past, support for concurrent programmingwas uneven among vendors. Concurrent

programming environments and tools were mostly

confined to specialized applications.

eal-time operating systems, in particular,

strongly supported concurrent programming, due

in some cases to a lac of memory protection.

+any real-time systems also demand pearesponsiveness.


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Why Bother with Concurrent Programming?

!he current trend in microprocessor design isparallelism.

Cloc speed wasn't the answer, and 7hit the

wall8.

+ulti-core CP9s increase both performance and

energy efficiency.

Destop and noteboo computers are now

parallel machines.


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#f your software application demands high

performance and:or responsiveness, you should

consider enabling it to tae advantage of the

parallelism inherent in today's computer systems.


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ot all software benefits from concurrency.

Profile your application.

Consider the cost:benefits.

!he learning curve is not as bad as you may

thin.


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What types of software benefit?

!he following conditions mar an application as a candidate for

concurrency;


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Concurrent Software Architecture

!wo main approaches to concurrent programming;

Process +odel

!hreading +odel


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Process Model

6pplication distributed across multiple processes.

Processes wor in parallel, running on separate

e$ecution units (CP9s or cores.)

9ni$ a great platform for Process +odel

applications, due to a good set of interprocess

functionality (shared memory, semaphores,process control)


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hreading Model

Parallelism achieved within a single process.

6dvantages;


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!ser Space "s# $ernel Space hreads

9ser *pace !hreads (79ser !hreads8);

Controlled by a scheduler lined into the process.Coordination with ernel scheduler re"uired.7Dynamic8 languages (Perl, Python, uby) use 9ser

!hreads (each with their own semantics.) ?ava utilizes9ser !hreads (called 7green threads8.)

@ernel *pace !hreads (7@ernel !hreads8);

Controlled only by ernel scheduler.When supported well by the &*, the better way to

implement threading.


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hreads in %inu&

&riginal eneration P&*#A !hreads (>P!) was

offered as a replacement for


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'endor Support

!hreading support varied among vendors.

#n 22E, a P&*#A standard, PBB.c (nown as

7Pthreads8) was issued, to standardize multi-threaded

programming. !his standard has largely remained the same,

with some minor changes.

Fendor support has improved (but # still don't trust themG)


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Current rends in Multi(hreaded Programming

&pen+P (www.openmp.org) is a toolit that aims

to simplify multi-threaded programming in C:CJJand K&!6.

*ome compilers now have switches that cause

generation of parallel code, without re"uiring any

special programming by the developer. *un

+icrosystems has this in their C:CJJ compiler.

*un's motto is 7let the compiler handle thecomplications of producing multi-threaded code.8
http://www.openmp.org/http://www.openmp.org/


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asell (www.hasell.org) is a language that aims to simplify multi-

threaded programming. !his afternoon, in DL from ;B to E;BB pm,a asell tutorial will be presented.

!ransactional +emory is a techni"ue to Iournal memory #:&, which

promises to alleviate some of the potential pitfalls of multi-threaded

programming. !here will be a short tal about this on Wednesday,

2;Bam-2;5Epm, Portland 0allroom.

!he >9 organization has developed a library for C, called >9 Pth

(for >9 Portable !hreads, see www.gnu.org:software:pth). Pth was a

foundation of the abandoned >P! proIect.

>9 also has their own &pen+P proIect (called >&+P,) which appears

to be inactive at this time.

!here are other &pen+P implementations.
http://www.haskell.org/http://www.gnu.org/software/pthhttp://www.gnu.org/software/pthhttp://www.haskell.org/


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#ntel Corporation has created a toolit, a CJJ class library, to

simplify mutli-threaded programming and also has a debugger andprofiler for threaded software. #ntel plans to release a new open-source

product for multi-threaded development at this &*C& (!uesday, 3;B

am /;BB noon, D2-5B.)

6 new &'eilly boo has Iust been released, titled #ntel !hreading0uilding 0locs.


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)ntel hreading Building Blocks *BB+

#ntel has tied together a number of different parallel

programming concepts and implemented them in !00.

!00 is only available for #ntel processors and those that

emulate them (i.e. 6+D). #ntel may open-source !00, in

which case you will be able to rebuild it for differentplatforms.

#f #ntel open-sources !00, be sure to chec whether critical

performance functionality has been moved into the #ntelcompilers. 6lso carefully chec licensing.

Do your own testing and benchmaring of !00.


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)ntel hreading Building Blocks *BB+

!00 contains different types of mute$es, for different

situations.

!00 seems to do a good Iob supporting manipulation of

comple$ data structures.

!00 seems to be aimed at parallel mathematical

operations.

Comple$ity doesn't go away, it Iust gets e$pressed

differently. #n terms of coding, !00 is in some ways more

comple$ than woring with Pthreads.

!00 is not standards compliant. #t is a proprietary 6P#.


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Pthreads

Wh Pth d ?


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Why Pthreads?

Pthreads is a good way to start learning about

concurrent programming.

Pthreads is an international standard. =1*, !6!

#* 6 >&&D !#>G


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Why Pthreads?

Pthreads get the Iob done.

1$amples of successful Pthreads applications;

6pache

+y*4et over it.

6ll computer systems share resources, in different

areas. =es, you should minimize shared data

access, but at some point your threads will need toshare some data.

While on the subIect of shared data...

)BM Cell Broadband 4ngine *CB45 or the 6Cell7+


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!he C01 has a main e$ecution core and up to 3 7*ynergistic

Processing 1lements8 (*P1s). *P1s are e$ecution cores.What maes them different and special, is they each have

their own memory. !his alleviates much of the trouble

associated with shared memory.

C01 has very fast data buses, to facilitate message passing

and broadband data transmission.

# find C01 the most interesting new processor architecture.



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#0+ has taen a hybrid approach to programming

C01, adding a library with functions applying to the*P1's.

1ach *P1 has dedicated memory. !his greatly

reduces the need for threads to share physical

memory.

System Considerations for Concurrency8Parallelism


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!o achieve the best results from concurrency, the entire

computer system needs to be designed with as much

parallelism as possible. !his means things such as;

Parallel networ interface controllers*imultaneous memory accessDedicated memory for e$ecution cores

1ven so, there are always going to be bottlenecs, there is

no way to escape this. !he way to minimize the effect of

bottlenecs is to increase processing speed at bottlenecpoints. !hus, system design becomes an e$ercise in

balancing bandwidth and concurrency.

Problems to a"oid when programming threads


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ace Conditions

Priority #nversion

Deadly 1mbrace

!hread unsafe libraries (due to reentrancy and

thread cancellation)

unning out of process resources

hings to do when working with Pthreads


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@eep things as clean and simple as possible

+inimize shared data

9ther opics *time permitting+


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!hread *cheduling

!hread Cancellation!est harnesses for our programsDebugging with >9 gdbCondition Fariables

Process resources and thread attributesCleanup functions!hread cancellation*cheduling Pthreads

*etting process resources

Summary

h i l h ti t i t d th t i d


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hours is only enough time to introduce the topic and

loo at some simple Pthreads e$amples.

Pthreads programming is "uite different than se"uential

programming. #t involves thining a bit differently about

what is happening with your code and is also a bit tricy.

+any people are comparing concurrent programming to

obIect-oriented programming, in that it re"uires a change ofthining to accommodate the paradigm shift. # thin this is a

good analogy.

Despite uneven implementation among vendors, Pthreads isproven technology that powers some of the most pervasive

and successful infrastructure software.

Summary *cont#+

&f Pth d i 't f #f I ( t f


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&f course, Pthreads isn't for everyone. #f you enIoy (out of

either pleasure or necessity) the advantages of woring with

dynamic languages, then by all means continue woring withthem. =our programs can still benefit from the threading

mechanisms of those languages. *ome people have

developed Python e$tensions, written in C, that allow them

to access Pthreads from their Python programs.

!hose of you developing server software, demanding high

performance, should definitely tae a close loo at Pthreads.

Download +y*4< source code and see how they have

harnessed Pthreads.

#f your software is mathematically intensive, you should tae

a loo at #ntel !hreading 0uilding 0locs (!00).


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!han" you #or coming$ en%oy the rest o# the sho&'

Adrien Lamothe

adrien(adriens&e)'com

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Pthreads Programming

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