Return a CompletableFuture instead of a Future from MassIndexer.start()

Description

The CompletableFutures introduced in Java 8 provide a much more powerful API than the old-style Futures do.
E.g. attaching callbacks would be much easier and elegant with a CompletableFuture.

Environment

None

Status

Assignee

Fabio Massimo Ercoli

Reporter

Marco Perazzo

Labels

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Suitable for new contributors

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Feedback Requested

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Components

Fix versions

Affects versions

5.x

Priority

Minor
Configure