Hi,
I've played around with core.async a bit but now I'm trying to use it for a
real project and I'm running into a problem getting data off a file and
into a channel on the JVM (i.e. as opposed to ClojureScript)
I have around 1GB of data sitting in a file. Each line of the file
contains a separate JSON document. There are different types of document
in the file and I would like use core.async to setup a pipeline of
concurrent operations as follows so I can start processing the data before
I've finished reading the file.
1. Stream the raw data out of the file one line at a time, parse it as JSON
and write each line to channel (1)
2. Read channel (1) and divide the messages up by type and write them to
new channels (2..n)
3. Read channels (2..n) and apply business logic as appropriate
I'd like the initial read to run in it's own thread because it will be IO
blocking. The others can run in core.async's thread pool
I'm running into problems getting channels (1) and (2) to talk to one
another. Here's my initial spike and I would expect it to write the 10
lines of json from the example file to stdout.
(defn file-to-chan [ch file]
(do
(async/thread
(with-open [rdr (io/reader file)]
(doseq [line (line-seq rdr)]
(>!! ch line))))
ch))
(defn parse-line [s]
(json/parse-string s (comp keyword str/lower-case)))
(def events (chan 1 (map parse-line)))
(go
(while true
(println (<! events))))
(file-to-chan events "10_events.json")
I have a few questions...
* Can anyone help me understand what's going wrong? (I'm sure it's
something silly, but I'm going cross eyed looking at it)
* It's effectively a batch process. Is this an appropriate use case for
core.async?
* If so, am I on the right track or is there a better way to approach this?
Many Thanks
Adrian
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