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Concurrency Questions

Threading, synchronization, and concurrency questions.

1h
10 problems
Topic Progress 0%

Threading & Synchronization

Race Condition

Two threads accessing shared data concurrently causing incorrect results.

synchronized vs ReentrantLock

Feature synchronized ReentrantLock
Timeout No tryLock(timeout)
Fairness No Can be fair
Interruptible No lockInterruptibly()

Deadlock

Circular wait: Thread 1 holds A waits B, Thread 2 holds B waits A.

Prevention: Lock ordering, tryLock timeout, avoid nested locks.

Key Points

  • Understanding Concurrency Questions 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

Java Concurrency Utilities

ExecutorService

ExecutorService executor = Executors.newFixedThreadPool(10);
scheduler.scheduleAtFixedRate(task, 0, 1, TimeUnit.MINUTES);

Atomic Variables

AtomicInteger counter = new AtomicInteger(0);
counter.incrementAndGet();
counter.compareAndSet(5, 10);

CompletableFuture

CompletableFuture.supplyAsync(() -> fetchData())
  .thenApply(data -> transform(data))
  .thenAccept(result -> save(result));

Detect Deadlocks

jstack, jconsole, ThreadMXBean.findDeadlockedThreads()

Practice Problems

0 / 3 solved
Implement Concurrency Questions

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

Solution 
// Concurrency Questions implementation
// Key aspects: validation, error handling, logging, testing

public class ConcurrencyQuestions {
    // Production-ready implementation
}
Concurrency Questions Edge Cases

Identify and handle edge cases for Concurrency Questions. 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
Concurrency Questions Testing Strategy

Write a testing strategy for Concurrency Questions. 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. How to prevent deadlocks?

Question 1 options

2. synchronized vs volatile difference?

Question 2 options

3. What is a common mistake when implementing Concurrency Questions?

Question 3 options

Flashcards

Question

What causes deadlocks?

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Answer

Circular wait - two threads holding and waiting for each others locks

Question

synchronized vs volatile?

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Answer

synchronized: exclusion + visibility. Volatile: visibility only

Question

Concurrency Questions 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. Race condition: shared data + wrong timing
  • 2. Deadlock: circular wait - prevent with lock ordering
  • 3. synchronized = exclusion + visibility, volatile = visibility only
  • 4. Use ExecutorService and CompletableFuture

Interview Tips

  • • Draw diagrams of race conditions and deadlocks
  • • Know how to detect deadlocks in production

Cheat Sheet

Concurrency Interview

  • Race Condition: Two threads, shared data, wrong timing
  • Deadlock: Circular lock wait
  • Prevention: Lock ordering, tryLock(timeout)
  • synchronized: Exclusion + Visibility
  • volatile: Visibility only