Java.Multithreading.List the principles you follow in multithreaded programming?

✅ 1. Minimize Shared Mutable State

The best way to avoid concurrency issues is not to share data at all.

• Prefer immutable objects
• Use thread-local storage when needed
• Copy-on-write or defensive copying strategies

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✅ 2. Prefer High-Level Concurrency Utilities

Don’t reinvent the wheel — Java provides robust tools in java.util.concurrent.

• Use Executors, ConcurrentHashMap, BlockingQueue, CountDownLatch, etc.
• Avoid managing Thread manually unless necessary

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✅ 3. Use Proper Synchronization

Shared state must be protected using:

• synchronized blocks or methods
• ReentrantLock, ReadWriteLock when fine-grained control is needed
• volatile for simple flags (visibility only, not atomicity)

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✅ 4. Avoid Busy Waiting

Avoid loops that burn CPU unnecessarily.

Use:

• wait()/notify()
• Condition.await()/signal()
• LockSupport.park()
• Semaphore, BlockingQueue, etc.

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✅ 5. Keep Critical Sections Short

Reduce lock contention and improve performance by limiting what’s inside a synchronized block.

synchronized (lock) {
    // Only do what absolutely needs locking
}

✅ 6. Use Thread-Safe Collections

Collections like HashMap, ArrayList are not thread-safe by default.

Use:

• ConcurrentHashMap, CopyOnWriteArrayList, ConcurrentLinkedQueue, etc.

✅ 7. Favor Immutability

Immutable objects require no synchronization — they’re naturally thread-safe.

Great for:

• Configuration
• Cache keys
• Messages passed between threads

✅ 8. Avoid Deadlocks

Deadlocks occur when:

• Threads wait on locks held by each other
• Circular waiting + hold and wait

Prevent with:

• Lock ordering (always acquire locks in the same order)
• Try using tryLock() with timeout
• Avoid holding multiple locks if possible

✅ 9. Use Thread Pools, Not New Threads

Creating threads manually is expensive and unscalable.

Use:

• ExecutorService (for pooled threads)
• ForkJoinPool (for divide-and-conquer)

✅ 10. Don’t Block in Compute-Heavy Threads

For CPU-bound threads, avoid blocking calls (I/O, sleep, wait).

• Use dedicated I/O thread pools for blocking ops
• Consider Reactive / Non-blocking frameworks if needed

✅ 11. Gracefully Handle Shutdown

• Always call executor.shutdown() or shutdownNow()
• Use awaitTermination() to block until completion
• Cleanup resources (e.g., connections, files)

✅ 12. Test with Concurrency in Mind

Bugs may only appear under specific interleaving of threads

Use:

• Tools like jUnit + awaitility, Stress tests
• Simulators like jcstress
• Thread.sleep() to simulate timing issues (during tests only!)

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🔥 Bonus: Golden Rules for Multithreaded Design

Rule	Summary
🧠 Design for Simplicity	Simpler code = fewer threading bugs
⛔ Don’t guess, measure	Profile, stress test, use thread dumps
🧪 Test like it’s production	Assume worst-case scheduling
🛠 Favor stateless or functional design	Easier to parallelize and test