java 39 lines · 6 steps

A thread-safe request counter with AtomicInteger

An AtomicInteger backs a lock-free counter that caps concurrent requests using compare-and-set.

Explained by highlit

Intermediate concurrency atomics lock-free compare-and-swap thread-safety

1import java.util.concurrent.atomic.AtomicInteger;
2 
3public final class RequestCounter {
4 
  private final AtomicInteger count = new AtomicInteger();
  private final int limit;
7 
  public RequestCounter(int limit) {
      this.limit = limit;
  }
11 
  public int increment() {
      return count.incrementAndGet();
  }
15 
  public int decrement() {
      return count.updateAndGet(current -> current > 0 ? current - 1 : 0);
  }
19 
  public boolean tryAcquire() {
      while (true) {
          int current = count.get();
          if (current >= limit) {
              return false;
          }
          if (count.compareAndSet(current, current + 1)) {
              return true;
          }
      }
  }
31 
  public int current() {
      return count.get();
  }
35 
  public int reset() {
      return count.getAndSet(0);
  }
39}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1AtomicInteger gives you thread-safe counting without locks or synchronized blocks.
2A compareAndSet retry loop lets you enforce conditional updates atomically under contention.
3updateAndGet clamps values in place so a decrement never drops below its floor.

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