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Showing posts from October, 2008

SysCache build for NHibernate 2.0.1GA

NHibernate 2.0.1GA is the latest binary download available, but it seems the NHibernate.Caches.SysCache binary release is lagging behind, as the download at Sourceforge was built against NHibernate 2.0.0. Here's a version of NHibernate.Caches.SysCache built against 2.0.1GA.

Dispatching: VTables vs. Runtime Tests and Casts

Object oriented languages like C# and Java use method dispatching techniques to select a concrete method to invoke when given a polymorphic type. By far the most common technique is the virtual method table , or vtable for short. Long ago I had updated the above Wikipedia page with information regarding alternative dispatch techniques. Research published a few years back indicated that dispatching through a vtable incurred astonishing overheads, as high as 50% of total execution time. Alternative dispatch techniques based on runtime tests, such as a linear sequence of if statements checking for the various concrete class types, or a sequence of nested if statements forming a binary search, were often more efficient on a variety of hardware. Vtables are rather flexible however, and the composition of a number of vtables can encode a variety of advanced dispatching behaviour. The .NET CLR utilizes vtables, and I've sketched out rough encodings of first-class functions, algebraic data