From d51c61d7983a1247bb7956e66d0d7f91512ac4d7 Mon Sep 17 00:00:00 2001
From: Tim Clemons <tim.clemons@base2s.com>
Date: Tue, 19 Nov 2013 17:45:12 -0800
Subject: [PATCH] Enclose cursor operations in a with-yielding call.

The with-yielding call will produce a lazy-seq in a
separate thread that will generate content from the
cursor.  The cursor will then be safely closed if the
seq is garbage collected or an error occurs.
---
 project.clj                  |  3 ++-
 src/clojure/monger/query.clj | 23 +++++++++++++----------
 2 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/project.clj b/project.clj
index 1f74b94..66fe1d4 100644
--- a/project.clj
+++ b/project.clj
@@ -7,7 +7,8 @@
                  [org.mongodb/mongo-java-driver "2.11.2"]
                  [com.novemberain/validateur    "1.5.0"]
                  [clojurewerkz/support          "0.19.0"]
-                 [ragtime/ragtime.core          "0.3.4"]]
+                 [ragtime/ragtime.core          "0.3.4"]
+                 [clj-yield                     "1.1"]]
   :test-selectors {:default     (fn [m]
                                   (and (not (:performance m))
                                        (not (:edge-features m))
diff --git a/src/clojure/monger/query.clj b/src/clojure/monger/query.clj
index bae17bf..cce2694 100644
--- a/src/clojure/monger/query.clj
+++ b/src/clojure/monger/query.clj
@@ -18,7 +18,8 @@
             [monger.cursor :as cursor :refer [add-options]])
   (:import [com.mongodb DB DBCollection DBObject DBCursor ReadPreference]
            [java.util List])
-  (:use [monger conversion operators]))
+  (:use [monger conversion operators]
+        [yield]))
 
 
 ;;
@@ -65,21 +66,23 @@
 
 (defn exec
   [{ :keys [^DBCollection collection query fields skip limit sort batch-size hint snapshot read-preference keywordize-fields options] :or { limit 0 batch-size 256 skip 0 } }]
-  (with-open [cursor (doto (.find collection (to-db-object query) (as-field-selector fields))
+  (with-yielding [y-out 1]
+    (with-open [cursor (doto (.find collection (to-db-object query) (as-field-selector fields))
                        (.limit limit)
                        (.skip  skip)
                        (.sort  (to-db-object sort))
                        (.batchSize batch-size)
                        (.hint (to-db-object hint)))]
-    (when snapshot
-      (.snapshot cursor))
-    (when read-preference
-      (.setReadPreference cursor read-preference))
-    (when options
+      (when snapshot
+        (.snapshot cursor))
+      (when read-preference
+        (.setReadPreference cursor read-preference))
+      (when options
       (add-options cursor options))
-    (map (fn [x] (from-db-object x keywordize-fields))
-         cursor)))
-
+      (loop []
+        (when (.hasNext cursor)
+          (yield y-out (from-db-object (.next cursor) keywordize-fields))
+          (recur))))))
 ;;
 ;; API
 ;;