Asynchronous method invocation: Difference between revisions

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It is equivalent to the [[IOU]] pattern described in 1996 by Allan Vermeulen.<ref>{{cite journal |last=Vermeulen |first=Allan |date=June 1996 |title=An Asynchronous Design Pattern |journal=[[Dr. Dobb's Journal]] |url=http://www.ddj.com/184409898 |accessdate=22 November 2008 }}</ref><ref>{{cite book |last=Nash |first=Trey |title=Accelerated C# 2008 | year=2007 |publisher=Apress |isbn=978-1-59059-873-3 |chapter=Threading in C# }}</ref>

In most programming languages a called method is executed synchronously, i.e. in the [[thread (computer science)|thread of execution]] from which it is invoked. If the method needstakes a long time to completioncomplete, e.g. because it is loading data over the internet, the calling thread is blocked until the method has finished. When this is not desired, it is possible to start a "worker thread" and invoke the method from there. In most programming environments this requires many lines of code, especially if care is taken to avoid the overhead that may be caused by creating many threads. AMI solves this problem in that it augments a potentially long-running ("synchronous") object method with an "asynchronous" variant that returns immediately, along with additional methods that make it easy to receive notification of completion, or to wait for completion at a later time.

One common use of AMI is in the [[active object]] design pattern. Alternatives are synchronous method invocation and [[futures and promises|future objects]].<ref name="active object">{{cite journal | last=Lavender | first=R. Greg |author2=[[Douglas C. Schmidt]] | title=Active Object | url=http://www.cs.wustl.edu/~schmidt/PDF/Act-Obj.pdf | format=PDF | accessdate=22 November 2008 }}</ref>