Meta tags:

Headings (most frequently used words):

edit, and, navigation, tools, load, link, store, conditional, contents, comparison, of, ll, sc, compare, swap, implementations, extensions, see, also, references, menu, personal, namespaces, views, search, contribute, print, export, languages,

Text of the page (most frequently used words):
the (44), and (29), load (18), store (16), this (12), #conditional (12), pdf (10), link (10), wikipedia (9), from (9), memory (9), acm (9), value (9), edit (8), #implementations (8), cas (8), articles (7), for (7), read (6), instructions (6), can (6), address (6), any (6), fail (6), not (5), 2017 (5), with (5), february (5), retrieved (5), architecture (5), 1145 (5), doi (5), free (5), isbn (5), eric (5), cache (5), see (5), are (5), other (5), updates (5), non (4), page (4), article (4), all (4), november (4), citations (4), lock (4), symposium (4), principles (4), laboratory (4), 2013 (4), also (4), computer (4), used (4), which (4), that (4), have (4), between (4), some (4), arm (4), there (4), even (4), compare (4), swap (4), needed (4), such (4), location (4), will (4), about (3), text (3), terms (3), 2021 (3), version (3), navigation (3), search (3), more (3), 2020 (3), transactional (3), org (3), reference (3), counting (3), podc (3), proceedings (3), distributed (3), computing (3), hagensen (3), jensen (3), broughton (3), technical (3), report (3), lawrence (3), livermore (3), national (3), new (3), trevor (3), brown (3), faith (3), ellen (3), ruppert (3), 978 (3), blocking (3), multi (3), operations (3), synchronization (3), reserved (3), risc (3), references (3), write (3), code (3), implementation (3), has (3), two (3), when (3), weak (3), pair (3), line (3), linked (3), another (3), citation (3), view (2), contact (2), privacy (2), policy (2), may (2), using (2), was (2), links (2), upload (2), file (2), changes (2), tools (2), learn (2), help (2), current (2), events (2), contents (2), talk (2), categories (2), clarification (2), january (2), specifically (2), marked (2), weasel (2), worded (2), phrases (2), unsourced (2), statements (2), lacking (2), 2015 (2), programming (2), alpha (2), 2004 (2), atomic (2), moir (2), annual (2), gary (2), jeffrey (2), 1987 (2), ucrl (2), archived (2), original (2), aap (2), approach (2), data (2), access (2), 4503 (2), general (2), university (2), practical (2), james (2), object (2), 193 (2), 2018 (2), instruction (2), isa (2), science (2), wiki (2), modify (2), typically (2), nesting (2), provide (2), primitive (2), implemented (2), they (2), implement (2), concurrent (2), list (2), tree (2), extensions (2), over (2), separate (2), only (2), into (2), requires (2), registers (2), old (2), being (2), bytes (2), block (2), same (2), modification (2), stronger (2), platforms (2), powerpc (2), allows (2), progress (2), cpus (2), sufficient (2), cause (2), through (2), than (2), many (2), operation (2), algorithms (2), occurred (2), since (2), been (2), restored (2), comparison (2), known (2), jump (2), http (2), web (2), cookie, statement, statistics, developers, mobile, disclaimers, available, under, additional, apply, site, you, agree, registered, trademark, profit, organization, wikimedia, foundation, inc, use, creative, commons, attribution, sharealike, license, last, edited, september, utc, polski, 日本語, français, deutsch, languages, printable, download, print, export, wikidata, item, cite, information, permanent, special, pages, related, what, here, recent, community, portal, contribute, donate, random, main, history, views, english, namespaces, log, create, account, contributions, logged, personal, menu, hidden, needing, constructs, concurrency, control, https, index, php, title, oldid, 1042059899, sites, 1993, axp, 151220, 151226, comm, reinholtz, kirk, december, users, journal, pointers, detlefs, martin, steele, guy, 2001, 190, 58113, 383, 383962, 384016, 8221, citeseerx, twentieth, bruner, john, pattin, jay, 97646, coherence, 97663, 2012, exclusive, shared, multiprocessors, 2014, 329, 342, 2656, 2555243, 2555267, ppopp, sigplan, practice, parallel, technique, trees, slides, 2065, 2484239, 2484273, pragmatic, primitives, structures, keir, fraser, cambridge, ucam, 579, freedom, larus, ravi, rajwar, 2007, morgan, claypool, 59829, 124, their, table, figures, section, particular, anderson, mark, 1995, universal, constructions, 184, 89791, 710, 224964, 224985, fourteenth, keno, fischer, julia, feature, preview, time, traveling, linux, bug, reporting, beckmann, nathan, carnegie, mellon, april, 740, fall, andrew, waterman, krste, asanović, eds, set, manual, volume, user, level, stanford, project, hardware, allow, pairs, mechanism, mcas, word, where, words, scattered, software, extension, call, llx, scx, relies, automated, generation, one, best, performing, actually, slightly, beating, based, skip, jdk, chromatic, binary, advantages, designing, reads, writes, required, design, philosophy, both, performed, fitting, naturally, common, hand, three, dependency, written, does, constraint, though, modern, chips, well, translate, internally, micro, cisc, x86, operand, isas, pipeline, define, platform, dependent, blocks, ranging, 2048, attempt, given, fails, normal, inside, anywhere, whole, space, former, most, these, wrap, loads, stores, although, vulnerable, false, sharing, example, face, changing, graphs, arbitrary, counter, reuse, otherwise, dcas, provides, architectural, guarantee, eventual, sequences, limited, length, double, lines, track, granularity, portion, whether, via, core, merely, ordinary, require, accessed, exclusively, configured, mode, llock, scond, arc, ldrex, strex, armv6, ldxr, stxr, mips, lwarx, stwcx, ldarx, stdcx, power, ldl_l, stl_c, ldq_l, stq_c, supported, nevertheless, equivalent, sense, either, manner, wait, difficult, emulate, additionally, stopping, running, paired, single, stepping, prevent, forward, making, debugging, tricky, real, always, succeed, question, exceptional, spuriously, older, broadcast, bus, called, researchers, breaks, theoretical, weakness, relative, context, switch, guaranteed, followed, detect, aba, problem, originally, proposed, multiprocessor, locked, sometimes, achieve, returns, while, subsequent, together, implements, multithreading, includes, but, how, remove, template, message, please, precise, introducing, improve, lacks, corresponding, inline, encyclopedia, wayback, machine, archive, 20221017015623, timestamps, capture, success, 2023, 2022, nov, oct, sep, dec, 2005, jul, 2026, captures,

Text of the page (random words):
load link store conditional wikipedia 193 captures 15 dec 2005 19 jul 2026 sep oct nov 17 2021 2022 2023 success fail about this capture timestamps the wayback machine http web archive org web 20221017015623 http en wikipedia org wiki load link store conditional load link store conditional from wikipedia the free encyclopedia jump to navigation jump to search this article includes a list of general references but it lacks sufficient corresponding inline citations please help to improve this article by introducing more precise citations february 2015 learn how and when to remove this template message in computer science load linked store conditional 1 ll sc sometimes known as load reserved store conditional 2 lr sc are a pair of instructions used in multithreading to achieve synchronization load link returns the current value of a memory location while a subsequent store conditional to the same memory location will store a new value only if no updates have occurred to that location since the load link together this implements a lock free atomic read modify write operation load linked is also known as load link citation needed load reserved 2 and load locked citation needed ll sc was originally citation needed proposed by jensen hagensen and broughton for the s 1 aap multiprocessor 1 at lawrence livermore national laboratory contents 1 comparison of ll sc and compare and swap 2 implementations 3 extensions 4 see also 5 references comparison of ll sc and compare and swap edit if any updates have occurred the store conditional is guaranteed to fail even if the value read by the load link has since been restored as such an ll sc pair is stronger than a read followed by a compare and swap cas which will not detect updates if the old value has been restored see aba problem real implementations of ll sc do not always succeed even if there are no concurrent updates to the memory location in question any exceptional events between the two operations such as a context switch another load link or even on many platforms another load or store operation will cause the store conditional to spuriously fail older implementations will fail if there are any updates broadcast over the memory bus this is called weak ll sc by researchers as it breaks many theoretical ll sc algorithms 3 weakness is relative and some weak implementations can be used for some algorithms ll sc is more difficult to emulate than cas additionally stopping running code between paired ll sc instructions such as when single stepping through code can prevent forward progress making debugging tricky 4 nevertheless ll sc is equivalent to cas in the sense that either primitive can be implemented in terms of the other in o 1 and in a wait free manner 5 implementations edit ll sc instructions are supported by alpha ldl_l stl_c and ldq_l stq_c powerpc power isa lwarx stwcx and ldarx stdcx mips ll sc arm ldrex strex armv6 and v7 and ldxr stxr arm version 8 risc v lr sc 2 arc llock scond some cpus which require the address being accessed exclusively to be configured in write through mode typically cpus track the load linked address at a cache line or other granularity such that any modification to any portion of the cache line whether via another core s store conditional or merely by an ordinary store is sufficient to cause the store conditional to fail all of these platforms provide weak clarification needed ll sc the powerpc implementation allows an ll sc pair to wrap loads and even stores to other cache lines although this approach is vulnerable to false cache line sharing this allows it to implement for example lock free reference counting in the face of changing object graphs with arbitrary counter reuse which otherwise requires double compare and swap dcas risc v provides an architectural guarantee of eventual progress for ll sc sequences of limited length some arm implementations define platform dependent blocks ranging from 8 bytes to 2048 bytes and an ll sc attempt in any given block fails if there is between the ll and sc a normal memory access inside the same block other arm implementations fail if there is a modification anywhere in the whole address space the former implementation is the stronger and most practical ll sc has two advantages over cas when designing a load store architecture reads and writes are separate instructions as required by the design philosophy and pipeline architecture and both instructions can be performed using only two registers address and value fitting naturally into common 2 operand isas cas on the other hand requires three registers address old value new value and a dependency between the value read and the value written x86 being a cisc architecture does not have this constraint though modern chips may well translate a cas instruction into separate ll sc micro operations internally extensions edit hardware ll sc implementations typically do not allow nesting of ll sc pairs 6 a nesting ll sc mechanism can be used to provide a mcas primitive multi word cas where the words can be scattered 7 in 2013 trevor brown faith ellen and eric ruppert implemented in software a multi address ll sc extension which they call llx scx that relies on automated code generation 8 they have used it to implement one of the best performing concurrent binary search tree actually a chromatic tree slightly beating the jdk cas based skip list implementation 9 see also edit non blocking synchronization read modify write transactional memory references edit a b s 1 project stanford computer science wiki 2018 11 30 a b c andrew waterman krste asanović eds 2017 05 07 7 2 load reserved store conditional instructions the risc v instruction set manual volume 1 user level isa version 2 2 pdf beckmann nathan synchronization pdf 15 740 computer architecture fall 2018 carnegie mellon university retrieved 23 april 2021 keno fischer 2020 05 02 julia 1 5 feature preview time traveling linux bug reporting retrieved 2020 05 14 james h anderson mark moir 1995 universal constructions for multi object operations podc 95 proceedings of the fourteenth annual acm symposium on principles of distributed computing acm pp 184 193 doi 10 1145 224964 224985 isbn 0 89791 710 3 see their table 1 figures 1 2 and section 2 in particular james r larus ravi rajwar 2007 transactional memory morgan claypool p 55 isbn 978 1 59829 124 7 keir fraser february 2004 practical lock freedom pdf technical report university of cambridge computer laboratory p 20 ucam cl tr 579 brown trevor ellen faith ruppert eric 2013 pragmatic primitives for non blocking data structures pdf podc 13 proceedings of the 2013 acm symposium on principles of distributed computing acm pp 13 22 doi 10 1145 2484239 2484273 isbn 978 1 4503 2065 8 see also slides trevor brown faith ellen eric ruppert 2014 a general technique for non blocking trees pdf ppopp 14 acm sigplan symposium on principles and practice of parallel programming acm pp 329 342 doi 10 1145 2555243 2555267 isbn 978 1 4503 2656 8 jensen eric h hagensen gary w broughton jeffrey m november 1987 a new approach to exclusive data access in shared memory multiprocessors pdf technical report lawrence livermore national laboratory ucrl 97663 archived from the original pdf on 2017 02 02 retrieved 2012 02 22 bruner john d hagensen gary w jensen eric h pattin jay c broughton jeffrey m 11 november 1987 cache coherence on the s 1 aap pdf technical report lawrence livermore national laboratory ucrl 97646 archived from the original pdf on 2 february 2017 retrieved 10 november 2013 detlefs d martin p moir m steele jr guy l 2001 lock free reference counting podc 01 proceedings of the twentieth annual acm symposium on principles of distributed computing acm pp 190 9 citeseerx 10 1 1 92 8221 doi 10 1145 383962 384016 isbn 1 58113 383 9 reinholtz kirk december 2004 atomic reference counting pointers c c users journal sites r l february 1993 alpha axp architecture comm acm 36 2 33 44 doi 10 1145 151220 151226 retrieved from https en wikipedia org w index php title load link store conditional oldid 1042059899 categories concurrency control programming constructs transactional memory hidden categories articles lacking in text citations from february 2015 all articles lacking in text citations all articles with unsourced statements articles with unsourced statements from november 2020 all articles with specifically marked weasel worded phrases articles with specifically marked weasel worded phrases from january 2017 wikipedia articles needing clarification from january 2017 navigation menu personal tools not logged in talk contributions create account log in namespaces article talk english views read edit view history more search navigation main page contents current events random article about wikipedia contact us donate contribute help learn to edit community portal recent changes upload file tools what links here related changes upload file special pages permanent link page information cite this page wikidata item print export download as pdf printable version languages deutsch français 日本語 polski 中文 edit links this page was last edited on 3 september 2021 at 01 01 utc text is available under the creative commons attribution sharealike license 3 0 additional terms may apply by using this site you agree to the terms of use and privacy policy wikipedia is a registered trademark of the wikimedia foundation inc a non profit organization privacy policy about wikipedia disclaimers contact wikipedia mobile view developers statistics cookie statement