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Exponential Backoff Transformer
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| /** | |
| * @param intervalMs The base interval to start backing off from. The function is: attemptNum^2 * intervalMs | |
| * @param retryAttempts The max number of attempts to retry this task or -1 to try MAX_INT times, | |
| */ | |
| public static <T> Observable.Transformer<T, T> backoff(final long intervalMs, final int retryAttempts) { | |
| return new Observable.Transformer<T, T>() { | |
| @Override | |
| public Observable<T> call(final Observable<T> observable) { | |
| return observable.retryWhen( | |
| retryFunc(intervalMs, retryAttempts), | |
| Schedulers.immediate() | |
| ); | |
| } | |
| }; | |
| } | |
| private static Func1<? super Observable<? extends Throwable>, ? extends Observable<?>> retryFunc(final long ms, final int attempts) { | |
| return new Func1<Observable<? extends Throwable>, Observable<Long>>() { | |
| @Override | |
| public Observable<Long> call(Observable<? extends Throwable> observable) { | |
| // zip our number of retries to the incoming errors so that we only produce retries | |
| // when there's been an error | |
| return observable.zipWith( | |
| Observable.range(1, attempts > 0 ? attempts : Integer.MAX_VALUE), | |
| new Func2<Throwable, Integer, Integer>() { | |
| @Override | |
| public Integer call(Throwable throwable, Integer attemptNumber) { | |
| return attemptNumber; | |
| } | |
| }) | |
| // flatMap the int attempt number to a timer that will wait the specified delay | |
| .flatMap(new Func1<Integer, Observable<Long>>() { | |
| @Override | |
| public Observable<Long> call(final Integer integer) { | |
| long newInterval = ms * ((long) integer * (long) integer); | |
| if (newInterval < 0) { | |
| newInterval = Long.MAX_VALUE; | |
| } | |
| // use Schedulers#immediate() to keep on same thread | |
| return Observable.timer(newInterval, TimeUnit.MILLISECONDS, Schedulers.immediate()); | |
| } | |
| }); | |
| } | |
| }; | |
| } |
Author
@plastiv sorry for missing this comment, but yes you're correct.
Author
OP updated with TimeUnit to be better aligned with mainline api's that work with time.
Just to make sure I understanding/using this correctly: This does never actually forward the last error, right? That is, after the last retry I will get an onCompleted() in my Subscriber and not an onError?
I think there is a problem in your code, since you use Schedulers.immediate() in the backoff, you shouldn't use
it again in retryFunc's Observable.timer, it will cause the other operation in retryFunc block, am I right?
@DavidMihola, I think you are right, I have encountered exactly the problem you mentioned.
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I understand that overwriting default scheduler with
immediate()would save switching between threads and keeping a main observable worker thread from releasing back to the pool. Is it a correct assumption?