Week 11: Data-Parallel Collections

Useful Resources

• Documentation for Scala Parallel Collections

• Splitters and Combiners

• Creating Custom Parallel Collections

• Code with examples, package parallel

Code Commentary

A short summary of the files from the accompanying code is given below, outlining the characteristic aspects of working with Scala Parallel Collections. We suggest you explore the files in the order they appear in the following list.

Measuring Performance

• package object parallel — a package object defining common functions used for benchmarking. warmedTimed is used to take advantage of JIT-based speed-up.

• ParDemoTimed — showcasing a simple parallel collection example. Notice the oddities with timing parallel vs. sequential execution.

• ParDemoWarmed — the same as before, but now with warmed-up times, hence a better comparison.

Basic Usage of Parallel Collections

• ParConfig — controlling the level of parallelism for a collection.

• GoodParallelism — showcasing an operation that allows for good parallelism.

• BadParallelism — a case of a bad parallel speed-up (or the lack thereof) due to introduced contention in the operation applied to a collection.

Caveats of Using Parallel Collections

• NonParallelizableCollections — comparing the inherent parallelism in different collections.

• NonParallelizableOperations — analysing parallelism allowed by certain operations.

• ParSideEffectsIncorrect and ParSideEffectsCorrect — parallel processing in the presence of side effects.

• ParNonCommutativeOperator — exploiting the effects of commutativity in parallel collections. ArrayBuffer preserves the ordering of elements, while Scala’s set does not.

• ParNonAssociativeOperator — exploiting the influence of operation associativity when processing parallel collections.

• ConcurrentCollectionsWrong and ConcurrentCollectionsGood — exploring interactions between parallel and concurrent collections. In the bad case, a sequential collection is used in a parallel setting, which leads to an error.

Parallel Splitters and Combiners

• ParString — implementation of a parallel immutable string

• ParStringSplitter — Recursive splitter for parallel strings

• ParStringSplitterTests — Testing parallel string splitter

• ParStringSplitterBenchmarks — benchmarks for string splitters

• ParStringCombiner — two-phase combiner for parallel strings

• ParStringCombinerTests — Testing parallel string combiner

• ParStringCombinerBenchmarks — benchmarks for combiners