Backoff calculation throws ArithmeticException after many iterations

[chringwer]

In case of a repeat with an exponential backoff the next delay will always be calculated based on the current iteration no matter which maximum value has been set.

reactor-addons/reactor-extra/src/main/java/reactor/retry/Backoff.java

Line 94 in a440eb7

Duration nextBackoff = firstBackoff.multipliedBy((long) Math.pow(factor, (context.iteration() - 1)));

After 63 iterations or less (depending on the initial value and factor) that will result in the following exception:

java.lang.ArithmeticException: Exceeds capacity of Duration: 9223372036854775808000000000
	at java.time.Duration.create(Duration.java:1006) ~[?:1.8.0_162]
	at java.time.Duration.multipliedBy(Duration.java:963) ~[?:1.8.0_162]
	at reactor.retry.Backoff$3.apply(Backoff.java:94) ~[reactor-extra-3.1.6.RELEASE.jar:3.1.6.RELEASE]
	at reactor.retry.Backoff$3.apply(Backoff.java:91) ~[reactor-extra-3.1.6.RELEASE.jar:3.1.6.RELEASE]
	at reactor.retry.AbstractRetry.calculateBackoff(AbstractRetry.java:68) ~[reactor-extra-3.1.6.RELEASE.jar:3.1.6.RELEASE]
	at reactor.retry.DefaultRepeat.repeatBackoff(DefaultRepeat.java:113) ~[reactor-extra-3.1.6.RELEASE.jar:3.1.6.RELEASE]
	at reactor.retry.DefaultRepeat.lambda$apply$1(DefaultRepeat.java:106) ~[reactor-extra-3.1.6.RELEASE.jar:3.1.6.RELEASE]

Once the current value is greater than max we should just set nextBackoff to maxBackoff and skip the computation.

[simonbasle]

Thanks for the report @chringwer. Would you be willing to try a PR against the 3.1.x branch?

In reactor/reactor-core#1122 I introduced an operator directly in core that does exponential backoff. It is most probably suffering from the same issue so I'll need to investigate that.

[simonbasle]

PR #166 fixes the issue. Core has been verified and is ok.