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README.md

JavaScriptKit Benchmarks

This directory contains performance benchmarks for JavaScriptKit.

Building Benchmarks

Before running the benchmarks, you need to build the test suite:

swift package --swift-sdk $SWIFT_SDK_ID js -c release

Running Benchmarks

# Run with default settings
node run.js

# Save results to a JSON file
node run.js --output=results.json

# Specify number of iterations
node run.js --runs=20

# Run in adaptive mode until results stabilize
node run.js --adaptive --output=stable-results.json

# Run benchmarks and compare with previous results
node run.js --baseline=previous-results.json

# Run only a subset of benchmarks
# Substring match
node run.js --filter=Call
# Regex (with flags)
node run.js --filter=/^Property access\//
node run.js --filter=/string/i

Identity Mode Benchmarks

Compare identityMode: "pointer" vs default ("none") for SwiftHeapObject wrapper caching. Both class variants are compiled into the same build via per-class @JS(identityMode: true) annotations, so no separate builds or config files are needed.

Requires --expose-gc for memory benchmarks.

Build once

swift package --swift-sdk $SWIFT_SDK_ID js -c release

Compare both modes in one run

node --expose-gc run.js --identity-mode=both --identity-iterations=1000000

Run only one mode

# Only pointer (identity-cached) classes
node --expose-gc run.js --identity-mode=pointer --identity-iterations=1000000

# Only non-identity classes
node --expose-gc run.js --identity-mode=none --identity-iterations=1000000

Additional options

# Control iteration count (default: 1000000)
node --expose-gc run.js --identity-mode=both --identity-iterations=500000

# Control pool sizes for reuse scenarios (default: 1)
node --expose-gc run.js --identity-mode=both --identity-reuse-pools=1,16

# Include memory profiling (heap snapshots before/during/after)
node --expose-gc run.js --identity-mode=both --identity-memory

# Combine with adaptive sampling
node --expose-gc run.js --identity-mode=both --adaptive

# Filter to specific identity benchmarks
node --expose-gc run.js --adaptive --filter=passBothWaysRoundtrip --identity-mode=both --identity-iterations=1000000

Identity Mode Scenarios

Scenario What it measures
passBothWaysRoundtrip Same object crossing boundary repeatedly (cache hit path)
getPoolRepeated_100 Bulk return of 100 cached objects (model collection pattern)
churnObjects Create, roundtrip, release cycle (FinalizationRegistry cleanup pressure)
swiftConsumesSameObject JS passes same object to Swift repeatedly
swiftCreatesObject Fresh object creation overhead (cache miss path)