Hi,
I've not yet seen any examples on how to deal with external processes
in Clojure (I hope I didn't overlook something in clojure-contrib).
The following is my attempt to start a sub-process and to pass through
stdout and stderr. The shell command prints out 1000 lines "hello"
and a final "command finished". The problem is that nothing is printed
by the Clojure program. If I increase the number of lines for example
to 2000 (change "head -1000" to "head -2000"), I see a lot of output,
but it is cut off somewhere in the middle and the final "command
finished" does never appear.
(use 'clojure.contrib.duck-streams)
(defn copy
[istream ostream]
(println "copy" istream ostream)
(loop [line (.readLine istream)]
(if line
(do
(.println ostream line)
(recur (.readLine istream))))))
(let [pb (new ProcessBuilder ["sh" "-c" "yes hello | head -1000; echo
command finished"])
proc (.start pb)
stdout (reader (.getInputStream proc))
stderr (reader (.getErrorStream proc))
stdout-agent (agent stdout)
stderr-agent (agent stderr)]
(send stdout-agent copy (writer *out*))
(send stderr-agent copy (writer *err*))
(await stdout-agent stderr-agent)
(.waitFor proc)
(shutdown-agents)
(println "done"))
Is this use of agents incorrect?
Why can the program terminate before all the output from the sub-
process has been passed through?
Is there a better way to synchronize with sub-processes in Clojure, or
is it necessary to synchronize completely at the Java level?
Thanks
Stephan
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