libre2-java

High-performance, thread-safe Java bindings to Google's RE2 regular expression library.

Built for production use in high-concurrency applications requiring safe, predictable regex matching with linear-time guarantees.

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Why RE2?

RE2 is fundamentally different from Java's built-in regex:

Feature	Java Regex	RE2
Time Complexity	Exponential (backtracking)	Linear (automata-based)
ReDoS Safe	❌ Vulnerable	✅ Immune
Thread Safety	Pattern thread-safe, Matcher not	Both thread-safe (Pattern shareable, Matcher per-thread)
Performance	Varies (can hang)	Predictable
Use Case	Trusted patterns	Untrusted patterns (user input, logs)

Critical for untrusted patterns: Processing user-supplied regex patterns on large datasets requires linear-time guarantees to prevent timeouts and ReDoS (Regular Expression Denial of Service) attacks.

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Why JNI over JNA?

Performance is our primary design goal. libre2-java uses JNI (Java Native Interface) instead of JNA (Java Native Access) for maximum performance:

Performance Comparison

Metric	JNA	JNI	Improvement
Call overhead	150-300 ns	50-100 ns	2-3x faster
Memory overhead	Pointer objects	Primitive longs	Less GC pressure
Type conversion	Runtime reflection	Compile-time binding	Faster marshalling

Actual Performance Results

Our benchmarks show the impact of JNI:

Cache hit latency:
  P50: 42 ns (0.042 μs)
  P99: 84 ns (0.084 μs)
  P99.9: 167 ns (0.167 μs)

High-concurrency throughput:
  100 threads × 10,000 ops = 1,000,000 operations
  Throughput: 4,126,502 ops/sec
  Duration: 242 ms

Scalability (ops/sec):
  1 thread:   5,561,735 ops/sec
  10 threads: 9,989,760 ops/sec
  50 threads: 7,181,793 ops/sec
  100 threads: 5,634,297 ops/sec

Why This Matters

libre2-java is designed for high-performance use cases like:

• Database regex indexes (SAI in Apache Cassandra)
• Log processing pipelines (millions of entries/second)
• Real-time pattern matching (security, monitoring)

Every microsecond matters at scale. With millions of regex operations per second, a 2-3x reduction in call overhead translates to significant throughput gains.

Trade-offs

JNI requires:

• Native code compilation (we handle this via CI/CD)
• Platform-specific binaries (we ship 4 platforms)
• JNI header generation (automated in build)

We accept these trade-offs because performance is non-negotiable for our use cases.

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Quick Start

// Basic usage
boolean matches = RE2.matches("\\d+", "123");  // true

// Reusable pattern (cached automatically)
Pattern pattern = RE2.compile("\\w+@\\w+\\.\\w+");
boolean isEmail = pattern.matches("user@example.com");  // true

// Pattern matching in text
try (Matcher matcher = pattern.matcher("Contact: admin@test.com")) {
    boolean found = matcher.find();  // true
}

That's it! Patterns are cached automatically. No manual cleanup needed for cached patterns.

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Key Features

🚀 Performance

• Automatic caching with LRU eviction (50,000 pattern default)
• Linear-time matching (no catastrophic backtracking)
• Concurrent compilation (100+ threads tested)
• Off-heap execution (native RE2 library)

🔒 Safety

• Thread-safe (Pattern shareable, comprehensive analysis performed)
• Reference counting (prevents use-after-free under concurrency)
• ReDoS immune (linear time guarantee)
• Resource limits (configurable max patterns, max matchers)
• Memory leak prevention (deferred cleanup, shutdown hooks)

⚙️ Configuration

• 7 tunable parameters (cache size, timeouts, limits)
• Production defaults optimized for high-memory deployments (128GB+ RAM)
• Validated configuration (catches misconfigurations at startup)
• Fully documented (see CONFIGURATION.md)

🧪 Testing

• 187 comprehensive tests (including concurrency, stress, edge cases)
• Verified on 4 platforms (macOS x86/ARM, Linux x86/ARM)
• No memory leaks (verified with deferred cleanup tests)
• No deadlocks (stress tested with 1000+ threads)

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Installation

Requirements

• Java 17+ (uses sealed classes, records, text blocks)
• SLF4J 2.0+ (provided scope - for logging)

Why "Provided" Dependencies?

libre2-java uses provided scope for SLF4J to avoid version conflicts:

• SLF4J (Simple Logging Facade for Java): Used for logging. libre2-java logs cache operations, resource tracking, and errors. Your application provides the SLF4J implementation (Logback, Log4j2, etc.).

Note: libre2-java uses JNI (not JNA) for native calls. No additional native access library is required - JNI is built into the JVM.

Maven

<dependency>
    <groupId>com.axonops</groupId>
    <artifactId>libre2-java</artifactId>
    <version>1.0.0-SNAPSHOT</version>
</dependency>

<!-- Your application must provide these dependencies: -->

<!-- SLF4J API - Required for logging -->
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>2.0.9</version>
</dependency>

<!-- SLF4J implementation (choose one) -->
<dependency>
    <groupId>ch.qos.logback</groupId>
    <artifactId>logback-classic</artifactId>
    <version>1.4.14</version>
</dependency>

JAR Size: 2.4 MB (includes native libraries for all 4 platforms)

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Basic Usage

Simple Matching

// One-off matching (pattern compiled and cached automatically)
boolean matches = RE2.matches("hello.*world", "hello beautiful world");  // true

// Case-insensitive
boolean matches = RE2.matches("HELLO", "hello", false);  // true (case-insensitive)

Pattern Reuse (Recommended)

// Compile once, use many times (retrieved from cache on subsequent calls)
Pattern emailPattern = RE2.compile("\\w+@\\w+\\.\\w+");

// Convenience method - handles Matcher creation/closure internally
boolean valid1 = emailPattern.matches("user@example.com");  // true
boolean valid2 = emailPattern.matches("invalid.email");      // false

// Explicit Matcher - always use try-with-resources
try (Matcher m = emailPattern.matcher("user@example.com")) {
    boolean valid = m.matches();  // true
}

Note: The pattern.matches(text) convenience method internally creates a Matcher and closes it. For explicit Matcher use, always use try-with-resources to ensure proper cleanup.

Searching in Text

Pattern pattern = RE2.compile("ERROR");

// Find pattern anywhere in text
try (Matcher matcher = pattern.matcher(logEntry)) {
    if (matcher.find()) {
        // Pattern found
    }
}

// Full match (entire string must match)
try (Matcher matcher = pattern.matcher("ERROR")) {
    if (matcher.matches()) {
        // Entire string matches
    }
}

Log Processing Example

// Server log analysis
Pattern errorPattern = RE2.compile("\\[ERROR\\].*");

String[] logLines = loadLogFile();  // 1 million lines

for (String line : logLines) {
    try (Matcher m = errorPattern.matcher(line)) {
        if (m.find()) {
            // Process error line
        }
    }
}
// Fast: Linear time, no backtracking, cached pattern

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Thread Safety

✅ Thread-Safe (Can Share Between Threads)

Pattern:

// Safe: Share Pattern between threads
Pattern sharedPattern = RE2.compile("\\d+");

// Thread 1
executor.submit(() -> {
    try (Matcher m = sharedPattern.matcher("123")) {
        return m.matches();
    }
});

// Thread 2
executor.submit(() -> {
    try (Matcher m = sharedPattern.matcher("456")) {
        return m.matches();
    }
});

❌ NOT Thread-Safe (Do Not Share)

Matcher:

// UNSAFE: Do not share Matcher between threads
Matcher matcher = pattern.matcher("test");

// Thread 1
matcher.matches();  // ❌ UNSAFE

// Thread 2
matcher.find();  // ❌ UNSAFE - concurrent access to same Matcher

// Fix: Create separate Matcher per thread

See Thread Safety Guide for details.

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Configuration

Default configuration works for most production deployments.

For custom configuration:

RE2Config config = RE2Config.builder()
    .maxCacheSize(100000)           // Cache up to 100K patterns
    .idleTimeoutSeconds(600)         // Evict after 10 min idle
    .deferredCleanupIntervalSeconds(2)  // Cleanup every 2 seconds
    .build();

// Note: Configuration currently uses static cache
// Custom config support coming in Phase 3

Configuration Parameters (7 total):

Parameter	Default	Purpose
cacheEnabled	true	Enable/disable automatic caching
maxCacheSize	50,000	Max cached patterns (~50-200MB)
idleTimeoutSeconds	300	Evict patterns idle > 5 minutes
evictionScanIntervalSeconds	60	Scan for idle patterns every 60s
deferredCleanupIntervalSeconds	5	Cleanup evicted patterns every 5s
maxSimultaneousCompiledPatterns	100,000	Max ACTIVE patterns (not cumulative)
maxMatchersPerPattern	10,000	Max matchers per pattern

See CONFIGURATION.md for detailed tuning guide.

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Performance

Benchmarks on modern hardware:

Operation	Time	Notes
Pattern compilation (cache miss)	~100-500 μs	One-time cost
Pattern compilation (cache hit)	~1-5 μs	From cache
Simple match	~5-50 μs	Linear in input size
Complex pattern match	~50-500 μs	Still linear
1MB log file scan	< 500 ms	Tested in test suite

vs Java Regex on ReDoS patterns:

Pattern	Input	Java Regex	RE2
(a+)+b	"a" × 30 + "x"	Hangs (seconds)	< 1 ms
(a*)*b	"a" × 30 + "x"	Hangs	< 1 ms

RE2 is always linear time - no surprises.

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Native Libraries

Pre-compiled native libraries embedded in JAR for:

• macOS x86_64 (Intel Macs)
• macOS aarch64 (Apple Silicon)
• Linux x86_64 (x86_64)
• Linux aarch64 (ARM64)

Libraries are:

• Securely built (git commit pinning, signature verification)
• Self-contained (statically linked, only system dependencies)
• Auto-detected (platform detection automatic)
• Extracted on first use (to temp directory)

See native/README.md for build process.

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Architecture

Component Overview

┌─────────────────────────────────────────────┐
│            User Application                 │
└──────────────────┬──────────────────────────┘
                   │
                   ▼
         ┌──────────────────┐
         │   RE2 API        │
         │  (Entry Point)   │
         └────────┬─────────┘
                  │
      ┌───────────┴───────────┐
      ▼                       ▼
┌────────────┐         ┌─────────────┐
│  Pattern   │◄────────│ PatternCache│
│ (Thread-   │         │ (LRU + Idle)│
│  Safe)     │         └──────┬──────┘
└─────┬──────┘                │
      │                 ┌─────▼──────────┐
      │                 │ IdleEviction   │
      │                 │ BackgroundTask │
      ▼                 └────────────────┘
┌────────────┐
│  Matcher   │
│ (Per-Thread│
│  Instance) │
└─────┬──────┘
      │
      ▼
┌────────────────┐
│  RE2 Native    │
│  (JNI → C++    │
│   → RE2)       │
└────────────────┘

Key Flows:

1. Compilation: Pattern.compile() → Cache check → Compile if miss → Cache result
2. Eviction: LRU (when full) + Idle (background, every 60s) + Deferred cleanup (every 5s)
3. Matching: Matcher → Pattern's native pointer → JNI call → RE2 C++ → Result

See ARCHITECTURE.md for detailed design.

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Resource Management

Automatic (Default - Recommended)

// Patterns from compile() are cached - don't close them
Pattern p = RE2.compile("test");
// ... use pattern ...
// No close() needed - cache manages lifecycle

Manual (Testing Only)

// For tests requiring real resource management
Pattern p = Pattern.compileWithoutCache("test");
try {
    // ... use pattern ...
} finally {
    p.close();  // Must close uncached patterns
}

Cleanup

Automatic cleanup happens via:

• LRU eviction: When cache exceeds 50K patterns
• Idle eviction: Patterns unused for 5+ minutes
• Deferred cleanup: Evicted patterns freed every 5 seconds
• Shutdown hook: Clean shutdown when JVM exits

No manual cleanup required in production code.

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Logging

All log messages prefixed with RE2: for easy filtering.

Log Levels:

• INFO: Cache initialization, library loading, eviction summaries
• DEBUG: Cache hits/misses, pattern compilation, resource tracking
• WARN: Patterns evicted while in use (deferred), config warnings
• ERROR: Compilation failures, native library errors

Example:

INFO  RE2: Pattern cache initialized - maxSize: 50000, idleTimeout: 300s, scanInterval: 60s, deferredCleanup: every 5s
DEBUG RE2: Cache miss - compiling pattern: \d+ (case=true)
DEBUG RE2: Cache hit - pattern: \d+ (case=true)

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Compatibility

Tested With:

• Java 17, 18, 19, 20, 21
• SLF4J 2.0+

Platforms:

• macOS 10.15+ (Intel and Apple Silicon)
• Linux (x86_64 and aarch64)
• Windows: Not supported

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Building

# Build JAR (includes all native libraries)
mvn clean package

# Run tests (187 tests)
mvn test

# Build native libraries (maintainers only)
# See native/README.md

For developers: Native libraries are pre-built and committed. You only compile Java code.

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Documentation

• CONFIGURATION.md - Complete configuration guide
• ARCHITECTURE.md - Design and internals
• DESIGN_DECISIONS.md - Why native binding (not pure Java)
• THREAD_SAFETY.md - Thread safety guarantees
• native/README.md - Native library build system

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Status

Current Version: 1.0.0-SNAPSHOT Milestones:

• ✅ v1.0.0-phase1: Core API with native integration
• ✅ v1.0.0-phase2: Full caching, configuration, thread safety verified

Production Ready: ✅ For production use in high-concurrency applications

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Security

Native Library Security:

• Built from pinned git commits (cryptographically immutable)
• Signature verified (Google engineer signatures checked)
• No external dependencies (self-contained, only system libs)
• Automated builds (GitHub Actions CI/CD)

Source:

• RE2: Commit 927f5d5... (2025-11-05, signed by Russ Cox)
• Abseil: Commit d38452e... (20250814.1 LTS)

See native/README.md for security details.

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License

libre2-java is licensed under the Apache License 2.0.

See LICENSE file for details.

Third-Party Licenses

This library bundles the RE2 regular expression library:

• Project: google/re2
• License: BSD-3-Clause
• Copyright: The RE2 Authors

The BSD-3-Clause license is fully compatible with Apache License 2.0.

Complete License Texts:

• Apache License 2.0: See LICENSE
• RE2 BSD-3-Clause: See THIRD_PARTY_LICENSES.md

License Compatibility

libre2-java (Apache 2.0) can be used in:

• Apache 2.0 licensed projects
• Proprietary projects
• Commercial projects
• Any project compatible with Apache 2.0

Attribution

When distributing libre2-java:

1. Include Apache License 2.0 (LICENSE file)
2. Include RE2 BSD-3-Clause license (THIRD_PARTY_LICENSES.md)
3. Include NOTICE file with attribution

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Support

Issues: GitHub Issues

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Acknowledgments

• Google RE2 Team: For the excellent RE2 library
• Russ Cox: RE2 maintainer
• Abseil Team: For Abseil C++ libraries

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See Also

• Google RE2 Project
• SLF4J
• RE2 Syntax Reference
• JNI Documentation