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

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

utils.go

@@ -20,7 +20,9 @@ import (
 	"encoding/base64"
 	"encoding/xml"
 	"io"
+	"os"
 	"strings"
+	"syscall"
 )
 
 // xmlDecoder provide decoded value in xml.
@@ -73,3 +75,60 @@ func contains(stringList []string, element string) bool {
 	}
 	return false
 }
+
+// shutdownSignal - is the channel that receives any boolean when
+// we want broadcast the start of shutdown
+var shutdownSignal chan bool
+
+// shutdownCallbacks - is the list of function callbacks executed one by one
+// when a shutdown starts. A callback returns 0 for success and 1 for failure.
+// Failure is considered an emergency error that needs an immediate exit
+var shutdownCallbacks []func() errCode
+
+// shutdownObjectStorageCallbacks - contains the list of function callbacks that
+// need to be invoked when a shutdown starts. These callbacks will be called before
+// the general callback shutdowns
+var shutdownObjectStorageCallbacks []func() errCode
+
+// Register callback functions that need to be called when process terminates.
+func registerShutdown(callback func() errCode) {
+	shutdownCallbacks = append(shutdownCallbacks, callback)
+}
+
+// Register object storagecallback functions that need to be called when process terminates.
+func registerObjectStorageShutdown(callback func() errCode) {
+	shutdownObjectStorageCallbacks = append(shutdownObjectStorageCallbacks, callback)
+}
+
+// Start to monitor shutdownSignal to execute shutdown callbacks
+func monitorShutdownSignal() {
+	go func() {
+		// Monitor processus signal
+		trapCh := signalTrap(os.Interrupt, syscall.SIGTERM)
+		for {
+			select {
+			case <-trapCh:
+				// Start a graceful shutdown call
+				shutdownSignal <- true
+			case <-shutdownSignal:
+				// Call all callbacks and exit for emergency
+				for _, callback := range shutdownCallbacks {
+					exitCode := callback()
+					if exitCode != exitSuccess {
+						os.Exit(int(exitCode))
+					}
+
+				}
+				// Call all object storage shutdown callbacks and exit for emergency
+				for _, callback := range shutdownObjectStorageCallbacks {
+					exitCode := callback()
+					if exitCode != exitSuccess {
+						os.Exit(int(exitCode))
+					}
+
+				}
+				os.Exit(int(exitSuccess))
+			}
+		}
+	}()
+}