Task on multithreading: thread-safe metric collector with efficient increment, key — string, value — counter.

For a thread-safe metric collector with a string key and counter value in Java, you can use ConcurrentHashMap<String, AtomicLong>.

• ConcurrentHashMap provides concurrent access without locks at the entire map level.
• AtomicLong allows efficient and atomic incrementing of the counter.

Example implementation:

import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicLong;

public class MetricsCollector {
    private final ConcurrentHashMap<String, AtomicLong> counters = new ConcurrentHashMap<>();

    public void increment(String key) {
        counters.computeIfAbsent(key, k -> new AtomicLong()).incrementAndGet();
    }

    public long getCount(String key) {
        AtomicLong count = counters.get(key);
        return count != null ? count.get() : 0L;
    }
}

This approach minimizes locking and ensures high performance under multithreaded access.