Collections.Pooled 1.0.1

Collections.Pooled

This library is based on classes from System.Collections.Generic that have been altered to take advantage of the new System.Span<T> and System.Buffers.ArrayPool<T> libraries to minimize memory allocations, improve performance, and/or allow greater interoperablity with modern API's.

Collections.Pooled supports both .NET Standard 2.0 (.NET Framework 4.6.1+) as well as an optimized build for .NET Core 2.2+. An extensive set of unit tests and benchmarks have been ported from corefx.

Benchmarks

• .NET Core
• .NET Framework

Collections

PooledList<T>

PooledList<T> is based on the corefx source code for System.Collections.Generic.List<T>, modified to use ArrayPool for internal array-storage allocation, and to support Span<T>.

There are some API changes worth noting:

• Find and FindLast have become TryFind and TryFindLast, following the standard .NET "try" pattern.
• The new PooledList<T>.Span property returns a Span<T> over the portion of the internal array store that is populated. This span can be further sliced, or passed into other methods that can read from or write to a span.
  • Enumerating the Span property can be more than twice as fast as enumerating the list itself, but as we are unable to do the normal "collection modified during enumeration" checks, please use with caution.
  • The list is unable to increment its version-checking flag when setting values via the Span. Therefore, "collection modified during enumeration" checks can be bypassed. Please use with caution.
• GetRange now returns a Span<T>. For example, foo.GetRange(5, 100) is equivalent to foo.Span.Slice(5, 100).
• CopyTo now takes a Span<T> and doesn't offer any start-index or count parameters. Use the Span property and slicing instead.
• AddRange and InsertRange can now accept a ReadOnlySpan<T>.
• The new AddSpan and InsertSpan methods ensure the internal storage has the capacity to add the requested number of items, and return a Span<T> that can be used to write directly to that section of the internal storage. Caveats about "collection modified during enumeration" checks apply here as well.
• Delegate types such as Predicate<T> and Converter<T1, T2> have been replaced with standard Func<> equivalents.
• PooledList implements IDisposable. Disposing the list returns the internal array to the ArrayPool. If you forget to dispose the list, nothing will break, but memory allocations will go up, and so will GC pauses.

Performance

Please review the benchmark links above for complete details. Performance and memory allocations both range from "on par with List<T>" to "far better than List<T>" depending on the operation.

For example, AddRange is a particular strength for PooledList. In the extreme case of using AddRange to add a million integers 5000 times, List<T> allocates 19.5 GB while PooledList<T> allocates 156 KB and gets it done in 13% of the time.