December 21st, 2012
(written by lawrence krubner, however indented passages are often quotes). You can contact lawrence at: email@example.com
Lamina treats a series of events as a graph. As an organizing idea, this seems like a very good idea.
One thing I quickly discovered is that a transactional queue is about ten times slower than an equivalent implementation using ConcurrentLinkedQueues. For this reason, the one significant change to in this latest version is that channel queues are no longer transactional by default.
This is a big enough change that it deserves some explanation. While compatibility with Clojure’s concurrency primitives is very important, in practice transactions don’t seem to be often used in the same applications that use channels. Changing to non-transactional by default gives us an order of magnitude improvement without any visible changes to most or all real-world uses of Lamina.
This is analogous to the changes to primitive numbers in Clojure 1.3, which greatly improves Clojure’s potential performance at the expense of a largely hypothetical use-case. However, this change was mostly a non-issue because BigIntegers are contagious, allowing the change of a single value to affect all other derived values.
…When we chain together channel operators, like
(->> ch (map* inc) (filter* even?))
we’re creating an implicit graph. Each callback triggers subsequent callbacks, possibly applying a transform or predicate, until the value comes to rest in a queue or terminal callback.
This graph, though, is completely opaque to us. All we know is that a series of functions will be called, and that if the chain of operators is long our stack trace can get pretty noisy. Given a long enough chain of operators, we might even get a stack overflow.