Add code for chapter06 for first 2 sections

clojure-lang/src/clojure_lang/chapter06.clj

@@ -0,0 +1,105 @@
+(ns clojure-lang.chapter06
+  (:require [taoensso.carmine :as car]
+            [clj-time.coerce :as ctc]
+            [clj-time.core :as ct]
+            [clojure.string :refer [starts-with?]]
+            [clojure-lang.util :refer [wcar* server-conn]]))
+
+
+;;;;;;;;;;;;;;;;;;;;;;
+;; 6.1 Autocomplete ;;
+;;;;;;;;;;;;;;;;;;;;;;
+
+;; Listing 6.1: The add_update_contact() function
+
+(defn add-update-contact
+  [user contact]
+  (let [ac-list (str "recent:" user)]
+    (wcar* (car/lrem ac-list 0 contact)
+           (car/lpush ac-list contact)
+           (car/ltrim ac-list 0 99))))
+
+
+(defn remove-contact
+  [user contact]
+  (wcar* (car/lrem (str "recent:" user) contact)))
+
+
+;; Listing 6.2: the fetch_autocomplete_list() function
+
+(defn fetch-autocomplete-list
+  [user prefix]
+  (let [list-key (str "recent:" user)
+        candidates (wcar* (car/lrange list-key 0 -1))]
+    (filter (fn [candidate]
+              (starts-with? candidate prefix))
+            candidates)))
+
+
+;; Listing 6.8: The acquire_lock() function
+
+(defn acquire-lock
+  [lockname & {:keys [acquire-timeout]
+               :or {acquire-timeout 10}}]
+  (let [identifier (str (java.util.UUID/randomUUID))
+        end (+ (ctc/to-long (ct/now))
+               acquire-timeout)]
+    (loop []
+      (cond
+        (< end (ctc/to-long (ct/now))) false
+        (= 1 (wcar* (car/setnx (str "lock:" lockname) identifier))) identifier
+        :else (do (Thread/sleep 100)
+                  (recur))))))
+
+
+;; Listing 6.10: The release_lock() function
+
+(defn release-lock
+  [lockname identifier]
+  (let [lock-key (str "lock:" lockname)]
+    (wcar* (car/watch lock-key)
+           (if (= identifier (car/get lock-key))
+             (car/del lock-key)
+             (car/unwatch lock-key)))))
+
+;; Listing 6.9: The purchase_item_with_lock() function
+
+(defn purchase-item-with-lock
+  [buyer-id item-id seller-id list-price]
+  (let [buyer-key (str "users:" buyer-id)
+        seller-key (str "users:" seller-id)
+        item-key (format "%s.%s" item-id seller-id)
+        inventory-key (str "inventory:" buyer-id)
+        price (wcar* (car/zscore "market:" item-key))
+        funds (wcar* (car/hget buyer-key "funds"))
+        lock-identifier (acquire-lock "market")]
+    (when (and (= price list-price)
+               (< price funds))
+      (car/atomic server-conn
+                  5
+                  (car/watch "market:" buyer-key)
+                  (car/multi)
+                  (car/hincrby seller-key "funds" (Integer/parseInt price))
+                  (car/hincrby buyer-key "funds" (- (Integer/parseInt price)))
+                  (car/sadd inventory-key item-id)
+                  (car/zrem "market:" item-id)))
+    (when lock-identifier
+      (release-lock "market" lock-identifier))))
+
+
+;; Listing 6.11: The acquire_lock_with_timeout() function
+
+(defn acquire-lock-with-timeout
+  [lockname & {:keys [acquire-timeout lock-timeout]
+               :or {acquire-timeout 10
+                    lock-timeout 10}}]
+  (let [identifier (str (java.util.UUID/randomUUID))
+        end (+ (ctc/to-long (ct/now))
+               acquire-timeout)]
+    (loop []
+      (cond
+        (< end (ctc/to-long (ct/now))) false
+        (= 1 (wcar* (car/setnx (str "lock:" lockname) identifier))) (do (wcar* (car/expire (str "lock:" lockname) lock-timeout))
+                                                                        identifier)
+        :else (do (Thread/sleep 100)
+                  (recur))))))