[yue9944882]

Bug

ItemExponentialFailureRateLimiter.when() (extended module, work-queue rate limiters) computes the backoff multiplier as 1 << exp:

long exp = failures.computeIfAbsent(item, k -> new AtomicLong()).getAndIncrement();
long d = maxDelay.toMillis() >> exp;
return d > baseDelay.toMillis() ? baseDelay.multipliedBy(1 << exp) : maxDelay;

exp is a long, but 1 << exp is evaluated in int arithmetic (the shift result type follows the left operand, and the distance is masked to 5 bits). Once exp reaches 31, 1 << 31 overflows to Integer.MIN_VALUE (and wraps for higher counts). When maxDelay is large enough that the baseDelay * 2^exp branch is still selected at that failure count, baseDelay.multipliedBy(...) then returns a negative Duration — never a valid backoff.

Fix

Compute the multiplier in long arithmetic: 1L << exp. This matches the long type of exp and of Duration.multipliedBy(long), and is behavior-preserving for all exp < 31 (where 1 << exp == 1L << exp).

-    return d > baseDelay.toMillis() ? baseDelay.multipliedBy(1 << exp) : maxDelay;
+    return d > baseDelay.toMillis() ? baseDelay.multipliedBy(1L << exp) : maxDelay;

Verification

Added a focused regression test highFailureCountStaysPositive that drives the item to exp == 31 with a large maxDelay and asserts the backoff stays positive and equals baseDelay * 2^31.

• Before fix: highFailureCountStaysPositive FAILS (negative duration).
• After fix: all 5 tests in ItemExponentialFailureRateLimiterTest PASS.

./mvnw -pl extended -am test -Dtest=ItemExponentialFailureRateLimiterTest -Dsurefire.failIfNoSpecifiedTests=false
Tests run: 5, Failures: 0, Errors: 0, Skipped: 0

Draft pending maintainer review.

[kubernetes-prow]

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