서킷 브레이커 패턴

Java code

import java.util.concurrent.atomic.*;
import java.util.function.Supplier;

public class CircuitBreaker {
    enum State { CLOSED, OPEN, HALF_OPEN }

    private final AtomicReference<State> state = new AtomicReference<>(State.CLOSED);
    private final AtomicInteger failureCount = new AtomicInteger(0);
    private final int threshold;
    private final long resetTimeout;
    private volatile long lastFailureTime;

    CircuitBreaker(int threshold, long resetTimeoutMs) {
        this.threshold = threshold;
        this.resetTimeout = resetTimeoutMs;
    }

    <T> T execute(Supplier<T> action, Supplier<T> fallback) {
        if (state.get() == State.OPEN) {
            if (System.currentTimeMillis() - lastFailureTime > resetTimeout) {
                state.set(State.HALF_OPEN);
            } else {
                System.out.println("[CB] OPEN - 폴백 실행");
                return fallback.get();
            }
        }
        try {
            T result = action.get();
            reset();
            return result;
        } catch (Exception e) {
            recordFailure();
            System.out.printf("[CB] 실패 %d/%d%n", failureCount.get(), threshold);
            return fallback.get();
        }
    }

    private void reset() {
        failureCount.set(0);
        state.set(State.CLOSED);
    }

    private void recordFailure() {
        int count = failureCount.incrementAndGet();
        lastFailureTime = System.currentTimeMillis();
        if (count >= threshold) {
            state.set(State.OPEN);
            System.out.println("[CB] 서킷 OPEN!");
        }
    }

    public static void main(String[] args) {
        CircuitBreaker cb = new CircuitBreaker(3, 5000);
        for (int i = 0; i < 5; i++) {
            String result = cb.execute(
                () -> { throw new RuntimeException("서버 장애"); },
                () -> "폴백 응답");
            System.out.println("결과: " + result);
        }
    }
}