Does doFinally execute on the same thread in Reactor

Question

Does doFinally execute on the same thread? Will below code block the main thread?

mono
.map(fileName -> asyncDownloadFile(fileName, folderName))
.doFinally(v -> {
    FileUtils.cleanDirectory(folderName); // this method is blocking
});

if so what is the best way to execute cleanDirectory in a separate thread in doFinally?

Answer 1

Wrap the blocking call in a Runnable and run it on a separate thread:

Runnable task = () -> {FileUtils.cleanDirectory(folderName)};

Mono<Object> cleanDirPromise = Mono.fromRunnable(task);

mono
.map(fileName -> asyncDownloadFile(fileName, folderName))
.doFinally(v -> {
    cleanDirPromise.subscribeOn(Schedulers.parallel()).subscribe();
});

Note: This will essentially be a fire-and-forget call where you won't really care about the result of cleanDirPromise.