RxSwift Sequence of observables from array

Question

On my application I have to download several files from Amazon S3, for that purpose I have created a function that download a single files and return and observable. I have also created a second function that I have called downloadAll. The purpose of this function is to download each S3 files sequentially.

As some of the files are big and there are a lot of files (more than 50) If I just merge all the observables I end up with a lot of timeouts from amazon because of concurrency.

What I have tried:

Merge with concurrency

    let observables = self.syncItem!.files.map { (f) in
        return Observable.of(f)
    }
    let o = Observable.from(observables).merge(maxConcurrent: 2)

Result: I get the two first files downloaded but the others are not been downloaded.

ConcatMap

    return Observable.from(self.syncItem?.files).concatMap({ (file) in
        return self.downloadS3File(file: file)
    })

Result: Only the first file been downloaded

**DownloadS3FileFunction is ommitted ... it is working ok for a single file download and its emit a File object upon download completion **

I have searched a LOT before asking the question. Can someone please help?

Daniel T. · Accepted Answer · 2019-08-10 22:30:57Z

2

If only the first file is downloaded when you use concatMap then the problem is in your downloadS3File(file:) function. It doesn't emit a completed event when it's finished downloading the file so the concatMap doesn't start the second download.

That's likely the problem with your other solution as well.

answered Aug 10, 2019 at 22:30

Daniel T.

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2 Comments

Noel Carcases Over a year ago

Actually I am only emitting a next event not complete... I will emit a complete event and return. Thanks for your feedback ! :D

Noel Carcases Over a year ago

yep that was the problem just setting observable.onComplete() after onNext fix the issue... thanks again

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