concept pcall in category clojure

This is an excerpt from Manning's book Clojure: The Essential Reference MEAP V30. Login to get full access to this book.

“pmap, pcalls and pvalues” executes the map operation on a separate thread thus creating a parallel map. Replacing map with “pmap, pcalls and pvalues” makes sense when the overall cost of handling the function f to separate threads is less than the execution of f itself. Long or otherwise processor-consuming operations usually benefit from using “pmap, pcalls and pvalues”.

pmap, pcalls and pvalues build a lazy sequence as the result of processing a set of expressions in parallel (using futures). Both pcalls and pvalues build on top of pmap. pmap has a similar interface to map, but transformations apply to the input in parallel:

(pmap + (range 10) (range 10)) ; #1
;; (0 2 4 6 8 10 12 14 16 18)

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pcalls builds on top of pmap accepting any number of functions as input. It then creates a lazy sequence from the results of calling the functions without arguments. pcalls is a good solution for side effecting parallel transformations: