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en>Thepigdog: /* See also */

2014-10-30T04:15:58Z

See also

← Older revision		Revision as of 06:15, 30 October 2014
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	~~In [[computer science]], the '''happened-before''' [[binary relation\|relation]] (denoted: <math>\to \;</math>)~~ is ~~a relation between the result of two events, such that if one event should happen before another event, the result must reflect that. Even if those events are~~ in reality executed out of order (usually to optimize program flow). This involves [[partially ordered set\|ordering]] events based on the potential [[causal relationships\|causal relationship]] of pairs of events in a concurrent system, especially [[asynchronous communication\|asynchronous]] [[distributed systems]]. It was formulated by [[Leslie Lamport]].<ref>Lamport, Leslie (1978). [http://~~research.microsoft~~.com/~~en-us~~/um/~~people/lamport/pubs/time-clocks.pdf "Time, Clocks~~ and ~~the Ordering of Events~~ in ~~a Distributed System"], ''Communications of the ACM'', 21(7), 558-565~~.~~</ref> In Java specifically, a '''happens-before''' relationship is a guarantee that memory written~~ to ~~by statement A is visible~~ to ~~statement B, that~~ is~~, that statement A completes its write before statement B starts its read~~.[http://~~docs.oracle.com/javase/tutorial/essential/concurrency/memconsist.html]~~		Jerrie is what you in many cases can call me but Which i don't like when regular people use my full determine. My his [http://pinterest.com/search/pins/?q=conversation conversation] and I chose to maintain in Massachusetts. What I love doing would be to play croquet now I have time period to take on new things. The job I've been occupying suitable for years is an sequence clerk. See what's new on excellent website here: http://[https://Www.Vocabulary.com/dictionary/prometeu.net prometeu.net]<br><br>Check out my webpage: [http://prometeu.net clash of clans gem generator no survey]

	~~The happened-before relation is formally defined as the least [~~[~~strict partial order]] on events such that~~:
	* If events <math>a \;</~~math> and <math>b \;<~~/~~math> occur on the same process, <math>a \to b\;</math> if the occurrence of event <math>a \;</math> preceded the occurrence of event <math>b \;</math>~~.
	* If event <math>a \;</~~math> is the sending of a message and event <math>b \;</math> is the reception of the message sent in event <math>a \;</math>, <math>a \to b\;<~~/~~math>~~.

	~~If there are other causal relationships between events in a given system, such as between the creation of a process and its first event, these relationships are also added to the definition~~.

	~~Like all strict partial orders, the happened-before relation is ''[[transitive relation\|transitive]]'', ''[[irreflexive relation\|irreflexive]]'' and ''[[antisymmetric relation\|antisymmetric~~]~~]'', i.e.:~~
	* <~~math~~>~~\forall a, b, c~~<~~/math~~>~~, if <math>a \to b\;<~~/~~math> and <math>b \to c\;<~~/~~math>, then <math>a \to c\;</math> (transitivity) ;~~
	* <math>\forall a, a \nrightarrow a</math> (irreflexivity) ;
	* <math>\forall a, b,</math> if <math>a \to b\;</math> then <math>b \nrightarrow a</math> (antisymmetry).

	~~The processes that make up a distributed system have~~ no knowledge of the happened-before relation unless they use a [[logical clock]], like a [[Lamport clock]] or a [[vector clock]]. This allows to design algorithms for [[mutual exclusion]] and tasks like debugging or optimising distributed systems.

	~~==See also==~~
	* [[Java Memory Model]]
	* [[Lamport timestamps]]

	~~==References==~~
	~~<references/>~~

	~~{{DEFAULTSORT:Happened-Before}}~~
	~~[[Category:Distributed computing problems]~~]

en>BreakfastJr: Copyedit + Changed a tagged link to go to where I assume it was always meant to go rather than a disambig page

2014-01-21T12:28:22Z

Copyedit + Changed a tagged link to go to where I assume it was always meant to go rather than a disambig page

← Older revision		Revision as of 14:28, 21 January 2014
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	Hi, ~~everybody! My name is Garfield.~~ <br>It is a ~~little about myself: I live~~ in ~~Switzerland, my city~~ of ~~Ziegelbrucke~~. ~~<br>It's called often Northern or cultural capital~~ of . ~~I've married 2 years ago~~.<br>~~I have two children - a son~~ (~~Jenifer~~) and the ~~daughter~~ (~~Jerald~~). ~~We all like Golfing~~.<br><br>~~Visit my web blog~~ ... [~~http~~://~~Www~~.~~aparus~~.~~ru/userinfo~~.~~php?uid~~=~~362569 Fifa 15 Coin generator~~]		In [[computer science]], the '''happened-before''' [[binary relation\|relation]] (denoted: <math>\to \;</math>) is a relation between the result of two events, such that if one event should happen before another event, the result must reflect that. Even if those events are in reality executed out of order (usually to optimize program flow). This involves [[partially ordered set\|ordering]] events based on the potential [[causal relationships\|causal relationship]] of pairs of events in a concurrent system, especially [[asynchronous communication\|asynchronous]] [[distributed systems]]. It was formulated by [[Leslie Lamport]].<ref>Lamport, Leslie (1978). [http://research.microsoft.com/en-us/um/people/lamport/pubs/time-clocks.pdf "Time, Clocks and the Ordering of Events in a Distributed System"], ''Communications of the ACM'', 21(7), 558-565.</ref> In Java specifically, a '''happens-before''' relationship is a guarantee that memory written to by statement A is visible to statement B, that is, that statement A completes its write before statement B starts its read.[http://docs.oracle.com/javase/tutorial/essential/concurrency/memconsist.html]

			The happened-before relation is formally defined as the least [[strict partial order]] on events such that:
			* If events <math>a \;</math> and <math>b \;</math> occur on the same process, <math>a \to b\;</math> if the occurrence of event <math>a \;</math> preceded the occurrence of event <math>b \;</math>.
			* If event <math>a \;</math> is the sending of a message and event <math>b \;</math> is the reception of the message sent in event <math>a \;</math>, <math>a \to b\;</math>.

			If there are other causal relationships between events in a given system, such as between the creation of a process and its first event, these relationships are also added to the definition.

			Like all strict partial orders, the happened-before relation is ''[[transitive relation\|transitive]]'', ''[[irreflexive relation\|irreflexive]]'' and ''[[antisymmetric relation\|antisymmetric]]'', i.e.:
			* <math>\forall a, b, c</math>, if <math>a \to b\;</math> and <math>b \to c\;</math>, then <math>a \to c\;</math> (transitivity) ;
			* <math>\forall a, a \nrightarrow a</math> (irreflexivity) ;
			* <math>\forall a, b,</math> if <math>a \to b\;</math> then <math>b \nrightarrow a</math> (antisymmetry).

			The processes that make up a distributed system have no knowledge of the happened-before relation unless they use a [[logical clock]], like a [[Lamport clock]] or a [[vector clock]]. This allows to design algorithms for [[mutual exclusion]] and tasks like debugging or optimising distributed systems.

			==See also==
			* [[Java Memory Model]]
			* [[Lamport timestamps]]

			==References==
			<references/>

			{{DEFAULTSORT:Happened-Before}}
			[[Category:Distributed computing problems]]

50.46.150.30: /* Related concepts, fix typo */

2011-11-22T07:33:19Z

Related concepts, fix typo

New page

Hi, everybody! My name is Garfield. It is a little about myself: I live in Switzerland, my city of Ziegelbrucke. It's called often Northern or cultural capital of . I've married 2 years ago. I have two children - a son (Jenifer) and the daughter (Jerald). We all like Golfing. Visit my web blog ... [http://Www.aparus.ru/userinfo.php?uid=362569 Fifa 15 Coin generator]