Threaded code: Difference between revisions

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{{Short description|ProgrammingProgram techniquewhose source code consists entirely of calls to functions}}

{{confuse|Multi-threaded programming|Jump threading}}

In [[computer science]], '''threaded code''' is a programming technique where the [[Source code|code]] has a form that essentially consists entirely of calls to [[subroutine]]s. It is often used in [[compiler]]s, which may generate code in that form or be implemented in that form themselves. The code may be processed by an [[interpreter (computing)|interpreter]] or it may simply be a sequence of [[machine code]] [[subroutine call|call]] instructions.

Threaded code has better [[code density|density]] than code generated by alternative generation techniques and by alternative [[calling convention]]s. In [[Cache (computing)|cached]] architectures, it may [[Execution (computing)|execute]] slightly slower.{{citation needed|date=February 2012}} However, a program that is small enough to fit in a [[computer processor]]'s [[CPU cache|cache]] may run faster than a larger program that suffers many [[cache miss]]es.<ref name="tuwien1">{{cite web|url=http://www.complang.tuwien.ac.at/forth/threading/ |title=Speed of various interpreter dispatch techniques V2}}</ref> Small programs may also be faster at [[thread switch|thread switching]]ing, when other programs have filled the cache.

Threaded code is best known for its use in many compilers of [[programming language]]s, such as [[Forth (programming language)|Forth]], many implementations of [[BASIC]], some implementations of [[COBOL]], early versions of [[B (programming language)|B]],<ref>Dennis M. Ritchie, [https://www.bell-labs.com/usr/dmr/www/chist.html "The Development of the C Language"], 1993. Quote: "The B compiler on the PDP-7 did not generate machine instructions, but instead 'threaded code' ..."</ref> and other languages for small [[minicomputer]]s and for [[amateur radio satellite]]s.{{citation needed|date=February 2016}}