了解这个Clojure代码

Question

我对Clojure很陌生，我一直在努力实现一些并发代码。我在网上找到了这段代码。有一个警告，它不是在Clojure中进行并发的正确方法，但我仍然想理解此代码。

(def *readers* (map #(agent %) '("one" "two" "three"))) 
(def *writers* (map #(agent %) '("four" "five"))) 
(def *mutex* (agent :unlocked)) 
(def *value* 0) 

; mutex implementation 
(defn lock [state who success-fn fail-fn] 
    (send who (if (= state :locked) fail-fn success-fn)) 
    :locked) 

(defn unlock [mutex] 
    :unlocked) 

; Must be invoked with send-off since this handler blocks 
(defn rand-sleep [state next-fn] 
    (Thread/sleep (rand-int 5)) 
    (send *agent* next-fn) 
    state) 

; Reader functions 
(declare try-read) 

(defn reader-got-lock [name] 
    (println (format "Thread %s says that the value is %d." name *value*)) 
    (send *mutex* unlock) 
    (send-off *agent* rand-sleep try-read) 
    name) 

(defn reader-did-not-get-lock [name] 
    (println (format "Thread %s tried to read the value, but could not." name)) 
    (send-off *agent* rand-sleep try-read) 
    name) 

(defn try-read [name] 
    (send *mutex* lock *agent* reader-got-lock reader-did-not-get-lock) 
    name) 

; Writer functions 
(declare try-write) 

(defn writer-got-lock [name] 
    (println (format "Thread %s is taking the lock." name)) 
    (def *value* (rand-int 10)) 
    (println (format "Thread %s is changing the value to %d." name *value*)) 
    (send *mutex* unlock) 
    (println (format "Thread %s is relasing the lock." name)) 
    (send-off *agent* rand-sleep try-write) 
    name) 

(defn writer-did-not-get-lock [name] 
    (println (format "Thread %s tried to write the value, but could not." name)) 
    (send-off *agent* rand-sleep try-write) 
    name) 

(defn try-write [name] 
    (send *mutex* lock *agent* writer-got-lock writer-did-not-get-lock) 
    name) 

(dorun (map #(send % try-write) *writers*)) 
(dorun (map #(send % try-read) *readers*)) 

具体我被困在这条线：

(defn try-write [name] 
    (send *mutex* lock *agent* writer-got-lock writer-did-not-get-lock) 
    name) 

应该锁定互斥锁，并呼吁无论是作家了锁或作家那样 - 不得到锁取决于互斥州。但是*agent*在哪里声明，还是访问当前代理的捷径？那么如何将state传递给锁，在上述情况下是*agent*还是*agent*是who？

Answer 1

*agent*是当前代理的捷径，由clojure隐式提供。 *agent*通过为who。最后的电话大致看起来是这样的：

(lock @*mutex* *agent* writer-got-lock writer-did-not-get-lock)