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intermediate Phase · Concurrency

Thread Safety

Write thread-safe code using immutability, synchronization, and atomics.

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Thread Safety

Thread-Safe Collections

Unsafe Safe Alternative
ArrayList CopyOnWriteArrayList
HashMap ConcurrentHashMap
HashSet CopyOnWriteArraySet

Thread Safety Patterns

// 1. Immutability
public record Point(int x, int y) {}

// 2. Thread-local
private static final ThreadLocal<SimpleDateFormat> formatter =
    ThreadLocal.withInitial(() -> new SimpleDateFormat("yyyy-MM-dd"));

// 3. Atomic operations
private final AtomicInteger counter = new AtomicInteger(0);

Thread Management

Thread Pools

ExecutorService pool = Executors.newFixedThreadPool(10);

Pool Types

  • Fixed: Fixed number of threads
  • Cached: Creates as needed
  • Scheduled: For delayed tasks
  • WorkStealing: ForkJoinPool

Best Practices

  • Size pools appropriately
  • Use meaningful thread names
  • Implement graceful shutdown
  • Monitor thread usage

Common Issues

  • Thread leaks
  • Context switching overhead
  • Deadlocks

Key Points

  • Understanding Thread Safety is essential for production systems
  • Always consider scalability and maintainability
  • Test thoroughly before deploying to production
  • Monitor performance and set up alerting

Common Patterns

  1. Validation: Always validate input at the boundary
  2. Error Handling: Use structured error responses
  3. Logging: Log key events for debugging
  4. Testing: Unit, integration, and load tests
  5. Documentation: Keep docs updated with code changes

Practice Problems

0 / 3 solved
Implement Thread Safety

Design and implement a solution for Thread Safety in a backend system. Consider scalability, error handling, and production readiness.

Solution 
// Thread Safety implementation
// Key aspects: validation, error handling, logging, testing

public class ThreadSafety {
    // Production-ready implementation
}
Thread Safety Edge Cases

Identify and handle edge cases for Thread Safety. What happens under high load, with invalid input, or during failures?

Solution 
// Edge case handling:
// 1. Null/empty input -> validation
// 2. High load -> rate limiting, queuing
// 3. Failures -> retries, circuit breaker
// 4. Concurrent access -> locks, idempotency
Thread Safety Testing Strategy

Write a testing strategy for Thread Safety. Include unit tests, integration tests, and performance tests.

Solution 
// Test plan:
// - Unit: 80% coverage target
// - Integration: API contracts
// - Performance: latency, throughput
// - Chaos: failure injection

Quiz

1. Thread-safe alternative to HashMap?

Question 1 options

2. Immutable objects are?

Question 2 options

3. What is a common mistake when implementing Thread Safety?

Question 3 options

Flashcards

Question

Thread-safe HashMap?

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Answer

ConcurrentHashMap

Question

Immutable objects thread safety?

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Answer

Always thread-safe (cannot be modified)

Question

Thread Safety best practices

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Answer

Follow SOLID principles, write clean code, test thoroughly, document decisions, and monitor in production.

Revision Notes

Key Takeaways

  • 1. Use ConcurrentHashMap instead of HashMap
  • 2. Immutable objects are inherently thread-safe
  • 3. ThreadLocal for per-thread data
  • 4. AtomicInteger for atomic operations

Interview Tips

  • • Use thread-safe collections
  • • Apply thread safety patterns

Cheat Sheet

Thread Safety

  • ConcurrentHashMap, CopyOnWriteArrayList
  • Immutable: always thread-safe
  • ThreadLocal: per-thread data
  • AtomicInteger: atomic counter