ReentrantLock

locks.clj

boot.user=> (def l (java.util.concurrent.locks.ReentrantLock.))
#'boot.user/l
boot.user=> (defn foo [] (future (.lock l) (println "foo is locking") (Thread/sleep 30000) (.unlock l)))
#'boot.user/foo
boot.user=> (defn bar [] (future (if (.tryLock l) (do (println "got the lock") (.unlock l)) (println "passing by"))))
#'boot.user/bar
boot.user=> (foo)
foo is locking
#future[{:status :pending, :val nil} 0x32c734d1]
boot.user=> (bar)
passing by
#future[{:status :pending, :val nil} 0x3501037a]
boot.user=> (bar)
got the lock
#future[{:status :pending, :val nil} 0x2a50aea9]
boot.user=> (.isLocked l)
false
boot.user=>