Does anyone know of any libraries for Clojure that wrap up non-blocking
file I/O?
I'm interested in one suitable for use with core.async on Java 7+.
Below is a naïve stab at a function that reads file and returns it on a
channel. It blocks somewhat (in the open and length calls), but overall, it
is trying to be fast and non-blocking enough to usable in one of the
core.async worker threads under mild load. Of course, there are lots of
things to be concerned about, such as whether it is safe to pass a
ByteBuffer across a channel (thread safety concerns), etc. It also puts
exceptions on the channel, so the client can use Nolen's <? macro [1].
I'd rather not be solving a problem alone that I believe lots of core.async
users will encounter.
(def asynch-file-executor (Executors/newFixedThreadPool 8))
(defn read-file
[file]
(let [ch (async/chan)
path (java.nio.file.Paths/get (java.net.URI. file))
fileChannel (AsynchronousFileChannel/open path
#{StandardOpenOption/READ} asynch-file-executor (make-array FileAttribute
0))
buffer (ByteBuffer/allocate (.length (.toFile path)))]
(.read fileChannel buffer 0 buffer
(proxy [CompletionHandler] []
(completed [result _]
(.close fileChannel)
(.flip buffer)
(async/go
(async/>! ch buffer)
(async/close! ch)))
(failed [e _]
(async/go
(async/>! ch e)
(async/close! ch)))))
ch))
[1] http://swannodette.github.io/2013/08/31/asynchronous-error-handling/
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