contro l l i ng the remote process. The implementation
of the method that interacts \\'ith the operating S\'Stem
would know t.he trad c-ofts
todetermine how to <llla
l yze the req uest tor maximum efficiency.
Com·crring a locative describing a Fortran 90 arrav
section to a "read memory section" method should be
casv: thev represen t nearlv the same thing. For �1 loca
tive that describes a distributed HPf arrav, Aard,·ark
would need to build ( p hysical ) memory section
descri ptions for each p lwsical process. This can be
done by iterati ng 01·er the phvsical processes and
building the memory secti on tor each process.
Itis
:� lso possible to build the me mon· sections t()l" ;11 1 the processes d uri ng; �1 single pass thro uf':h the louri,·c , bur rhc pertcmn�11Kc gJins nu1· nor be large enough w w;1 1-ranr the added comploitv.
Differing Values
Using H PF to distrib u te an arr;n· often partitions irs clements Jmong the processes . ScaL1rs, ho11·c,·cr, �HT generally rcpliutcd and mav be e xpected ro kwc the same 1-;liue i n uch pmccss . There �1rc c1scs, thu ugh , where sccmi ngil' repli cated sc1 L1rs 111;1,. 110t h;11·c the S;lmc value. DO l oops th;lt do not requ i re daL1 to be com mun icated bet�,·ccn processes do nor h ;ln: sl·n ch roniJ.ation poi n ts :�nd can become out
of J
llnsc
, resulting i n their indexes ,mel other pri1·;1tizcd ' ;u·iablcsh<ll·ing d i ffere n t ,·al ues. Functions c1lkcl 11 i r h i n a
F o R A L L construct often run 1 11depcndcn til· of e;Kh
orhe1·, cwsing the a1·gu menrs ;tnd loc�11 ''<lri,lblcs in one process to he cl ifkrcnr ti·om those in ,w othcr.
A
debugger should be aware rh:�r ,·alucs might d i fkr :� nd adjust the p1·cscnt�1tion of such l';ll ues accordi ng�\.Aardvark's ;1pprcK1ch is to ddl n e a nc11· kind of value object c11led
chj/(Tinp,
mlues ro rcprescm <1 ,.;1luc ti·om a sem;unicalil' single sou rce th;H docs nor iLl\T thesame va l u e ti-om <11 1 i ts actual sources.
A
user
inr crbcc em detect rbis ki nd oh·:� J u e and d i spb1· it in d i fte rc m 11·�1\'S, [or example, based Oil CO! HOt ;md/or the size of the data .Referring ag.1 i n to figure 4, tilL prog;Llm "·'1' l ll ter r upted while e;Kh process 11':\S o.ccu ting the hl iKtion
M A N D E L V A L called with in a F O R A L L . Lme 2 sh o11·�
th�lt the �1rgumcnt X "·as dctnmined to h�n·e d i fte ri ng
\';l lues. This usn i n terhcc docs not sho11· :�l l the ,.;1 l u cs ;H this f�oi nt; �1 brgc n u mber of , a lucs could d i str,Kt t h e user ti·om the c u rrent objccti,·c of d iscclluing; where the process stopped. Insrod , it sho"·s an i n dicl tion that the ,·alucs arc d i ftcrenr ;llong; 11 ith the n-pc of
the \'ariab lc . Notice thar the other t11·o argu men ts,
N M I N �md N M A X , a rc presented as in tcg;crs; tiKI h,l,·c
the same val u e in a l l processes. Line 12 1·cquc sts to sec
the va lue of X . Line
1 3
;1g:1 i n sh o11·s th�u the ,·a lues �1rcd itkrellt, and lines 1 4 through
1 8
s ho" the process n u mber :md the \';liuc ti·om the process.To b u i l d a d i ftcring ,.,1lues object, A�1rLil-�1rk re;llb rhc ,·alucs tor a replicated sca lar ti·om cK h f� roccss . H. a l l the V<li ucs ;lre bit-wise cqu;ll, thev arc considned to be the S<ll11C and a st;md ard ( si n gl e ) ,.;1l u e object is returned . Otherwise, a d i ftcring ,·al ucs object is con structed ti·om the sc,·er;ll ,.�1l ucs. For n u m eric d;lLl, this ;1 pproach see ms rcason�1bk. Ifrhc ' al u e of a sc1Lu· inte ger vari�1blc I N T V A R is 4 on all the processes, then 4 1s �1 rcason;lble ( sin gle ) l'�l l u c for I N T V A R . I f thc ,·:�lue of
I N T v A R is 4 on some processors :�nd 5 011 others, no
single ,·aluc is rc1sonable. For 110I1!1lt m cr i c th ra ;md flOi nters, there i s the possibi l i tl' of blsL· J�ositi1 es and E1lsc neg:lti,·cs. The iclul tor uscr - d e tincd t1ves is ro compare the tlelds rcc u rsi,-clv. Poi nters that arc scman-
rical i l· the s.1mc em point to targets located at difti:renr mc mo1T ,1ddrcsscs tor u nrelated reasons, leading to d i fti:rcnr lncmor,· add ress ,·al ucs :�nd therefore a f:llse positi\'c . To corrccrlv d erdi.:rencc rhe poi mcrs, though, r\:1 1·d,·ark IKtds tile difkrc n t mc lllOrv :�dd ress \'�l lues. In short, it is rcJson<lble to test n u meric data and cre :trc a single ,·aluc object or a d ilkring \'J i u cs object, �m d it <lflf�Clrs rc1sona h l c to do the S<lmc to r non n u meric d a u , despite the possibi l irv ot"a rcc h n ie<1l ly b lsc kimi oh·;1luc object.
Currcmil', d i fferi ng ,.:1lucs d o nor participate in ��t-ith mctic. Tlur is, the expression I N T v A R . L T . 5 is v;1lid i f
I N T v A R is :1 single ,.,1l ue hut causes an e rror to be sig
!l;lled i f I N T V A R is a d i tkring \·alue. lvb ny cases could he nude ro 11·ork, bur some cases dct\' resol u tion . I n the
I N T V A R . L T . 5 ClSc, ifaiJ 1 aJues of i N T V A R ;u·e Jc�, rJ1an
5 or aJJ :1rc greater rhan or equal ro 5, then it is reason <lhlc to coll,lf�sc the result into a single ,.;1lue, . T R u E . m
. F A L S E . , respcctil ch-. I f some 1;1 lues ,\IT less than 5
;lnd some are not , it also seems reasonable to crcatc a diikri ng ' .1l ucs object rhar holds rhe ditk1i
ng
resu lts. What if I N T V A R . L T . 5 is used �1s the condition of a l11·c;1kpoim ,md some ''<li ucs of I N T v A R <1re less th;m 5 and some .1rc 11ot; The bre<lkpoint should prohJb!l cwse rhc process ( and aJI the phvsical processes) to rcm<1i n sroi�JKd . I t is unclcu· 11·hethcr Jrithmcric on d i fre nng ,.,1lues " ou[cl be usdi.d ro users or i f it wouldk.1d to more conti1 sion than it wou l d clear up. Unmet Cha llenges
H I'� prcscms <1 ' ,1rict1· of chal lenges rhar A�1rd1·ark docs nor \'c t ;lddrcss. Some o t-these cb�tl lcngcs ;lrc not in common pr<ll'ticc, gi1·ing them l o11· f1riorit,·. Some ;l iT rccem 11ith H I)� Version 2 . 0
�
1nd :�rc being used" i rh incn:.1sing ti-cq uenC\·. Some o f rh c ch;lllcngcs, tor C \ ,1!11f�lc, ;1 debugger- i n i tiated u l l of a n H P � proce d u re, :11T tedious to :�ddrcss correctlv.
Mapped Scalars
l r is possible ro distri bute a scala1· so thar the sccuar is not h i l h-replicated .1-The compiler 11 ould need to emit sufti cicm debugging i n t(m11:1tion, ll' hich wou ld probablv be a ' irru<1l �uT,l\' dcscri pto1· 11 ith an �lin\· r:mk ot" 0 and a no117ero tcmpbte ,·;mk. A1rd1-ark wou ld probabJv model ir using its o isti ng loc1D\'C r()[ HP� 'llTJVS, also ll'ith an :l!T;l\. rank ofO and ;lppropriarc template intcm11ation . Replica ted Arrays
U n l c�s orhcr"·isc spcc i tlcd, Dll; ITAL's H PF compiler rcplic1tcs ;lrravs Ir is possi ble to rq�licatc JIT<l�'S opl ic i th' ;md to ;th gn ;l!Ta,·s ( and Sellar ) so that the\' arc p.1rti;1lh· rcplicncd . Ctl lTc ntll·, A<1rd v;11·k docs n ot d e tect a l"Cf�l i cncd ;HTJ\', despite the svm bol c1blc or r u n -time dc�criptor i n d i cni ng th;H it is replicated. As a resu l t, A11·d,·ark determ i nes a single process fro m 11 hich w krch cKh arrJ\' c l c m c m . For ti.i l l v rep l i cated
JIT<l\'S, r\Jrchark shoul d reJd the JIT�\\' from
e:1ch
process and process them with the difkri ng val ues
algorithms. Corrccrl�' processing :�rra\'s rhar are par
ti:�lly repl icated is not JS easy as processing u nrep l i
CJted o r fu l ly repl icated arrays. lfrhe odd col um ns .1re
on processes 0 and
l,while the even col umns are on
processes
2�1 nd 3, no single process contains the entire
aiT<\1'.