Editing Read-copy-update (section)

{{Short description|Synchronization mechanism}}
In [[computer science]], '''read-copy-update''' ('''RCU''') is a [[synchronization (computer science)|synchronization]] mechanism that avoids the use of [[lock (computer science)|lock]] primitives while multiple [[thread (computing)|threads]] concurrently read and update elements that are linked through [[pointer (computer programming)|pointers]] and that belong to shared [[data structure]]s (e.g., [[linked lists]], [[Tree (data structure)|trees]], [[hash table]]s).<ref name=":0">{{Cite book|last=Tanenbaum|first=Andrew|title=Modern Operating Systems|publisher=Pearson|year=2015|isbn=9781292061429|edition=4th|location=USA|pages=148}}</ref>

Whenever a thread is inserting or deleting elements of data structures in [[shared memory]], all readers are guaranteed to see and traverse either the older or the new structure, therefore avoiding inconsistencies (e.g., dereferencing [[null pointer]]s).<ref name=":0" />

It is used when performance of reads is crucial and is an example of [[space–time tradeoff]], enabling fast operations at the cost of more space. This makes all readers proceed as if there were no [[synchronization (computer science)|synchronization]] involved, hence they will be fast, but also making updates more difficult.