Add a generic registerShutdown function for graceful exit (#2344)

* Add a generic registerShutdown function for graceful exit
* Add shutdown callback test case

utils_test.go

@@ -0,0 +1,42 @@
+/*
+ * Minio Cloud Storage, (C) 2016 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package main
+
+import (
+	"testing"
+)
+
+// ShutdownCallback simulates a successful exit here, all registered
+// shutdown callbacks need to return exitSuccess for this test to succeed
+func TestShutdownCallback(t *testing.T) {
+	// Register two callbacks that return success
+	registerObjectStorageShutdown(func() errCode {
+		return exitSuccess
+	})
+	registerShutdown(func() errCode {
+		return exitSuccess
+	})
+
+	shutdownSignal = make(chan bool, 1)
+	shutdownSignal <- true
+	// Start executing callbacks and quit if everything is fine
+	monitorShutdownSignal()
+
+	// Infinite loop here simulates an infinite running program
+	for {
+	}
+}