Skip to content

parallel-filter.md

Latest commit

 

History

History
75 lines (48 loc) · 2.31 KB

parallel-filter.md

File metadata and controls

75 lines (48 loc) · 2.31 KB

parallelFilter

Signature: parallelFilter<T>(data: T[], predicate: (item: T) => boolean): T[] — imported from perry/thread.

Filters an array in parallel across all available CPU cores. Returns a new array containing only the elements where the predicate returned a truthy value. Order is preserved.

Basic Usage

{{#include ../../examples/runtime/thread_snippets.ts:parallel-filter-basic}}

How It Works

Input: [a, b, c, d, e, f, g, h]     (8 elements, 4 CPU cores)

  Core 1: [a, b] → test → [a]       (b filtered out)
  Core 2: [c, d] → test → [c, d]    (both kept)
  Core 3: [e, f] → test → []        (both filtered out)
  Core 4: [g, h] → test → [h]       (g filtered out)

Output: [a, c, d, h]                 (concatenated in original order)

Each core independently tests its chunk of elements. Results are merged in the original element order after all threads complete.

Why Not Just Use .filter()?

Regular .filter() runs on a single thread. For large arrays with expensive predicates, parallelFilter distributes the work:

{{#include ../../examples/runtime/thread_snippets.ts:parallel-filter-vs-filter}}

The tradeoff: parallelFilter has overhead from copying values between threads. Use it when the predicate is expensive enough to justify that cost.

Capturing Variables

Like parallelMap, the predicate can capture outer variables. Captures are deep-copied to each thread:

{{#include ../../examples/runtime/thread_snippets.ts:parallel-filter-capture}}

Mutable variables cannot be captured — the compiler rejects this at compile time.

Examples

Filtering Large Datasets

{{#include ../../examples/runtime/thread_snippets.ts:parallel-filter-large}}

Combined with parallelMap

{{#include ../../examples/runtime/thread_snippets.ts:parallel-filter-combined}}

Predicate with Heavy Computation

{{#include ../../examples/runtime/thread_snippets.ts:parallel-filter-heavy}}

Performance

Use parallelFilter when:

  • The array has many elements (hundreds or more)
  • The predicate function does meaningful work per element
  • You need to keep the UI responsive during filtering

For trivial predicates on small arrays, regular .filter() is faster (no threading overhead).