Merge pull request #3 from FarmLogs/uncaught-exceptions

Implement uncaught exception handling in dispatcher.

project.clj

@@ -1,10 +1,11 @@
-(defproject com.farmlogs/dispatcher "1.0.0"
+(defproject com.farmlogs/dispatcher "1.0.1"
   :description "Library to start specific workers in a jar"
   :min-lein-version "2.0.0"
   :plugins [[s3-wagon-private "1.2.0"]]
   :repositories {"farmlogs-internal" {:url "s3p://fl-maven-repo/mvn"
                                       :username ~(System/getenv "AMAZON_KEY")
                                       :passphrase ~(System/getenv "AMAZON_SECRET")}}
-  :dependencies [[org.clojure/clojure "1.6.0"]]
+  :dependencies [[org.clojure/clojure "1.6.0"]
+                 [org.clojure/tools.logging "0.3.1"]]
   :main dispatcher.core
   :profiles {:uberjar {:aot :all}})

src/dispatcher/core.clj

@@ -2,7 +2,9 @@
   (:gen-class)
   (:require [clojure.edn :as edn]
             [clojure.java.io :as io]
-            [clojure.string :refer [join]]))
+            [clojure.string :refer [join]]
+            [dispatcher.exceptions.uncaught
+             :refer [register-uncaught-exception-handler]]))
 
 (defn read-config
   []
@@ -20,6 +22,7 @@
    (let [config-keys (keys (read-config))]
      (println "Please specify one of:" (join ", " config-keys) ".")))
   ([entry-point & args]
+   (register-uncaught-exception-handler)
    (-> (read-config)
        (get entry-point)
        (dispatch args))))

src/dispatcher/exceptions/protocols.clj

@@ -0,0 +1,7 @@
+(ns dispatcher.exceptions.protocols)
+
+(defprotocol HandleException
+  "This protocol is an extension point enabling services to define
+  behavior specific to a particular exception type when it's caught by
+  the uncaught exception handler."
+  (handle [exception thread]))

src/dispatcher/exceptions/uncaught.clj

@@ -0,0 +1,17 @@
+(ns dispatcher.exceptions.uncaught
+  (:require [clojure.tools.logging :as log]
+            [dispatcher.exceptions.protocols :as p]))
+
+;; Define default behavior for all exceptions. This can be overridden
+;; by downstream code. It can also be extended to more specific types.
+(extend-protocol p/HandleException
+  Throwable
+  (handle [exception thread]
+    (log/error exception "Uncaught error on thread:" (.getName thread))))
+
+(defn register-uncaught-exception-handler
+  ([]
+   (Thread/setDefaultUncaughtExceptionHandler
+    (reify Thread$UncaughtExceptionHandler
+      (uncaughtException [_ thread throwable]
+        (p/handle throwable thread))))))