
Java Concurrency
- 419 installs
- 40 repo stars
- Updated January 5, 2026
- pluginagentmarketplace/custom-plugin-java
java-concurrency is an agent skill that designs thread-safe Java services using executors, locks, concurrent collections, and structured async patterns for developers who need scalable, correct backends under load.
About
java-concurrency is an agent skill in pluginagentmarketplace/custom-plugin-java focused on designing thread-safe Java services for production backends. The skill covers executors, locks, concurrent collections, and structured async patterns so concurrent code stays correct under load. Developers reach for java-concurrency when building or refactoring Java services where race conditions, pool sizing, or shared mutable state threaten reliability. The skill emphasizes scalable backend patterns rather than single-threaded prototypes. Use it during service implementation when concurrency primitives and async structure must be chosen deliberately before traffic hits the system.
- Executor and thread-pool sizing patterns
- Lock-free versus synchronized tradeoffs
- Concurrent collection selection guidance
- Race and deadlock diagnostic tactics
- CompletableFuture and structured task flows
Java Concurrency by the numbers
- 419 all-time installs (skills.sh)
- +7 installs in the week ending Aug 4, 2026 (Skillselion tracking)
- Ranked #14 of 89 Java & JVM skills by installs in the Skillselion catalog
- Data as of Aug 4, 2026 (Skillselion catalog sync)
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| Installs | 419 |
|---|---|
| repo stars | ★ 40 |
| Last updated | January 5, 2026 |
| Repository | pluginagentmarketplace/custom-plugin-java ↗ |
How do you design thread-safe Java services under load?
Design thread-safe Java services using executors, locks, concurrent collections, and structured async patterns for scalable, correct backends under load.
Who is it for?
Java backend developers implementing or refactoring services that must stay correct under concurrent requests and shared state.
Skip if: Developers working on single-threaded scripts, frontend code, or JVM performance tuning without concurrency design needs.
When should I use this skill?
A Java backend task involves executors, locks, concurrent collections, race conditions, or structured async under load.
What you get
Concurrency-safe service designs with executor configs, lock strategies, concurrent collection choices, and structured async patterns.
- Thread-safe service design
- Executor and lock strategy recommendations
Files
Java Concurrency Skill
Master Java concurrency patterns for thread-safe applications.
Overview
This skill covers concurrency from basic threads to virtual threads (Java 21+), including thread pools, synchronization, and CompletableFuture.
When to Use This Skill
Use when you need to:
- Write thread-safe code
- Implement parallel processing
- Use async programming patterns
- Tune thread pools
- Debug concurrency issues
Topics Covered
Thread Management
- Thread lifecycle and states
- Daemon vs user threads
- Interrupt handling
Synchronization
- synchronized, volatile
- Lock interfaces (ReentrantLock)
- Atomic operations
Executors
- ThreadPoolExecutor configuration
- ForkJoinPool
- Virtual Threads (Java 21+)
CompletableFuture
- Async execution
- Chaining and composition
- Exception handling
Quick Reference
// Virtual Threads (Java 21+)
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
IntStream.range(0, 10_000).forEach(i ->
executor.submit(() -> processRequest(i)));
}
// CompletableFuture composition
CompletableFuture<Result> result = fetchUser(id)
.thenCompose(user -> fetchOrders(user.id()))
.thenApply(orders -> processOrders(orders))
.exceptionally(ex -> handleError(ex))
.orTimeout(5, TimeUnit.SECONDS);
// Thread pool configuration
ThreadPoolExecutor executor = new ThreadPoolExecutor(
10, 50, 60L, TimeUnit.SECONDS,
new ArrayBlockingQueue<>(1000),
new ThreadPoolExecutor.CallerRunsPolicy()
);
// Lock with timeout
ReentrantLock lock = new ReentrantLock();
if (lock.tryLock(1, TimeUnit.SECONDS)) {
try {
// critical section
} finally {
lock.unlock();
}
}Thread Pool Sizing
| Workload | Formula | Example |
|---|---|---|
| CPU-bound | cores | 8 threads |
| I/O-bound | cores * (1 + wait/compute) | 80 threads |
Troubleshooting
| Problem | Cause | Solution |
|---|---|---|
| Deadlock | Circular lock | Lock ordering, tryLock |
| Race condition | Missing sync | Add locks/atomics |
| Thread starvation | Unfair scheduling | Fair locks |
Debug Commands
jstack -l <pid> > threaddump.txt
jcmd <pid> Thread.printUsage
Skill("java-concurrency")# java-concurrency Configuration
# Category: general
# Generated: 2025-12-30
skill:
name: java-concurrency
version: "1.0.0"
category: general
settings:
# Default settings for java-concurrency
enabled: true
log_level: info
# Category-specific defaults
validation:
strict_mode: false
auto_fix: false
output:
format: markdown
include_examples: true
# Environment-specific overrides
environments:
development:
log_level: debug
validation:
strict_mode: false
production:
log_level: warn
validation:
strict_mode: true
# Integration settings
integrations:
# Enable/disable integrations
git: true
linter: true
formatter: true
{
"$schema": "http://json-schema.org/draft-07/schema#",
"title": "java-concurrency Configuration Schema",
"type": "object",
"properties": {
"skill": {
"type": "object",
"properties": {
"name": {
"type": "string"
},
"version": {
"type": "string",
"pattern": "^\\d+\\.\\d+\\.\\d+$"
},
"category": {
"type": "string",
"enum": [
"api",
"testing",
"devops",
"security",
"database",
"frontend",
"algorithms",
"machine-learning",
"cloud",
"containers",
"general"
]
}
},
"required": [
"name",
"version"
]
},
"settings": {
"type": "object",
"properties": {
"enabled": {
"type": "boolean",
"default": true
},
"log_level": {
"type": "string",
"enum": [
"debug",
"info",
"warn",
"error"
]
}
}
}
},
"required": [
"skill"
]
}Java Concurrency Guide
Overview
This guide provides comprehensive documentation for the java-concurrency skill in the custom-plugin-java plugin.
Category: General
Quick Start
Prerequisites
- Familiarity with general concepts
- Development environment set up
- Plugin installed and configured
Basic Usage
# Invoke the skill
claude "java-concurrency - [your task description]"
# Example
claude "java-concurrency - analyze the current implementation"Core Concepts
Key Principles
1. Consistency - Follow established patterns 2. Clarity - Write readable, maintainable code 3. Quality - Validate before deployment
Best Practices
- Always validate input data
- Handle edge cases explicitly
- Document your decisions
- Write tests for critical paths
Common Tasks
Task 1: Basic Implementation
# Example implementation pattern
def implement_java_concurrency(input_data):
"""
Implement java-concurrency functionality.
Args:
input_data: Input to process
Returns:
Processed result
"""
# Validate input
if not input_data:
raise ValueError("Input required")
# Process
result = process(input_data)
# Return
return resultTask 2: Advanced Usage
For advanced scenarios, consider:
- Configuration customization via
assets/config.yaml - Validation using
scripts/validate.py - Integration with other skills
Troubleshooting
Common Issues
| Issue | Cause | Solution |
|---|---|---|
| Skill not found | Not installed | Run plugin sync |
| Validation fails | Invalid config | Check config.yaml |
| Unexpected output | Missing context | Provide more details |
Related Resources
- SKILL.md - Skill specification
- config.yaml - Configuration options
- validate.py - Validation script
---
Last updated: 2025-12-30
Java Concurrency Patterns
Design Patterns
Pattern 1: Input Validation
Always validate input before processing:
def validate_input(data):
if data is None:
raise ValueError("Data cannot be None")
if not isinstance(data, dict):
raise TypeError("Data must be a dictionary")
return TruePattern 2: Error Handling
Use consistent error handling:
try:
result = risky_operation()
except SpecificError as e:
logger.error(f"Operation failed: {e}")
handle_error(e)
except Exception as e:
logger.exception("Unexpected error")
raisePattern 3: Configuration Loading
Load and validate configuration:
import yaml
def load_config(config_path):
with open(config_path) as f:
config = yaml.safe_load(f)
validate_config(config)
return configAnti-Patterns to Avoid
❌ Don't: Swallow Exceptions
# BAD
try:
do_something()
except:
pass✅ Do: Handle Explicitly
# GOOD
try:
do_something()
except SpecificError as e:
logger.warning(f"Expected error: {e}")
return default_valueCategory-Specific Patterns: General
Recommended Approach
1. Start with the simplest implementation 2. Add complexity only when needed 3. Test each addition 4. Document decisions
Common Integration Points
- Configuration:
assets/config.yaml - Validation:
scripts/validate.py - Documentation:
references/GUIDE.md
---
Pattern library for java-concurrency skill
#!/usr/bin/env python3
"""
Validation script for java-concurrency skill.
Category: general
"""
import os
import sys
import yaml
import json
from pathlib import Path
def validate_config(config_path: str) -> dict:
"""
Validate skill configuration file.
Args:
config_path: Path to config.yaml
Returns:
dict: Validation result with 'valid' and 'errors' keys
"""
errors = []
if not os.path.exists(config_path):
return {"valid": False, "errors": ["Config file not found"]}
try:
with open(config_path, 'r') as f:
config = yaml.safe_load(f)
except yaml.YAMLError as e:
return {"valid": False, "errors": [f"YAML parse error: {e}"]}
# Validate required fields
if 'skill' not in config:
errors.append("Missing 'skill' section")
else:
if 'name' not in config['skill']:
errors.append("Missing skill.name")
if 'version' not in config['skill']:
errors.append("Missing skill.version")
# Validate settings
if 'settings' in config:
settings = config['settings']
if 'log_level' in settings:
valid_levels = ['debug', 'info', 'warn', 'error']
if settings['log_level'] not in valid_levels:
errors.append(f"Invalid log_level: {settings['log_level']}")
return {
"valid": len(errors) == 0,
"errors": errors,
"config": config if not errors else None
}
def validate_skill_structure(skill_path: str) -> dict:
"""
Validate skill directory structure.
Args:
skill_path: Path to skill directory
Returns:
dict: Structure validation result
"""
required_dirs = ['assets', 'scripts', 'references']
required_files = ['SKILL.md']
errors = []
# Check required files
for file in required_files:
if not os.path.exists(os.path.join(skill_path, file)):
errors.append(f"Missing required file: {file}")
# Check required directories
for dir in required_dirs:
dir_path = os.path.join(skill_path, dir)
if not os.path.isdir(dir_path):
errors.append(f"Missing required directory: {dir}/")
else:
# Check for real content (not just .gitkeep)
files = [f for f in os.listdir(dir_path) if f != '.gitkeep']
if not files:
errors.append(f"Directory {dir}/ has no real content")
return {
"valid": len(errors) == 0,
"errors": errors,
"skill_name": os.path.basename(skill_path)
}
def main():
"""Main validation entry point."""
skill_path = Path(__file__).parent.parent
print(f"Validating java-concurrency skill...")
print(f"Path: {skill_path}")
# Validate structure
structure_result = validate_skill_structure(str(skill_path))
print(f"\nStructure validation: {'PASS' if structure_result['valid'] else 'FAIL'}")
if structure_result['errors']:
for error in structure_result['errors']:
print(f" - {error}")
# Validate config
config_path = skill_path / 'assets' / 'config.yaml'
if config_path.exists():
config_result = validate_config(str(config_path))
print(f"\nConfig validation: {'PASS' if config_result['valid'] else 'FAIL'}")
if config_result['errors']:
for error in config_result['errors']:
print(f" - {error}")
else:
print("\nConfig validation: SKIPPED (no config.yaml)")
# Summary
all_valid = structure_result['valid']
print(f"\n==================================================")
print(f"Overall: {'VALID' if all_valid else 'INVALID'}")
return 0 if all_valid else 1
if __name__ == "__main__":
sys.exit(main())
Related skills
FAQ
What Java concurrency primitives does java-concurrency cover?
java-concurrency covers executors, locks, concurrent collections, and structured async patterns for thread-safe Java services. The skill targets scalable backend correctness when multiple threads access shared state under load.
When should a developer invoke java-concurrency?
java-concurrency should be invoked while building or refactoring Java backend services where concurrent requests, shared mutable state, or executor configuration affect correctness. The skill focuses on design patterns rather than JVM profiling.