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Multithreading and Synchronization in Java - write code to manage synchronized threads

Python/Codingmedium0.5 min readPremium

**Why Synchronization:** Multiple threads accessing shared mutable state cause race conditions. synchronized guarantees mutual exclusion; ReentrantLock offers finer control (tryLock, fairness). **Scalability:** synchronized is coarse—contention becomes bottleneck. Prefer: (1)...

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Frequency
Low
Asked at 1 company
Category
179
questions in Python/Coding
Difficulty Split
127E|24M|28H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
Walmart
Key Concepts Tested
partition

Why This Question Matters

This medium-level Python/Coding question appears frequently in data engineering interviews at companies like Walmart. While less common, it tests deeper understanding that distinguishes strong candidates. Mastering the underlying concepts (partition) will help you answer variations of this question confidently.

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Break this problem into components. Identify the core trade-offs involved, then walk the interviewer through your reasoning step by step. Demonstrate awareness of edge cases and production considerations - this is what separates good answers from great ones.

Expert Answer
93 words

Why Synchronization: Multiple threads accessing shared mutable state cause race conditions. synchronized guarantees mutual exclusion; ReentrantLock offers finer control (tryLock, fairness).

Scalability: synchronized is coarse—contention becomes bottleneck. Prefer: (1) ConcurrentHashMap for concurrent maps. (2) AtomicInteger/Long for counters. (3) Lock-free structures where possible. (4) Partition state: each thread owns a shard—no contention.

Cost: Context switching and lock contention under high concurrency. At Walmart-scale ingestion, we use ExecutorService with bounded pool and ConcurrentHashMap for in-memory aggregation—avoids lock contention on shared counter.

ExecutorService executor = Executors.newFixedThreadPool(4);
ConcurrentHashMap<String,AtomicLong> counts = new ConcurrentHashMap<>();
executor.submit(() -> counts.computeIfAbsent(k, v->new AtomicLong(0)).incrementAndGet());

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According to DataEngPrep.tech, this is one of the most frequently asked Python/Coding interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.

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