control: Implement service command 'stop,restart,status'. (#2883)

- stop - stops all the servers.
- restart - restart all the servers.
- status - prints status of storage info about the cluster.

cmd/service.go

@@ -0,0 +1,121 @@
+/*
+ * 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 cmd
+
+import (
+	"os"
+	"os/exec"
+	"syscall"
+)
+
+// Represents a type of an exit func which will be invoked upon service signal.
+type onExitFunc func(err error)
+
+// Represents a type for all the the callback functions invoked upon service signal.
+type cleanupOnExitFunc func() error
+
+// Type of service signals currently supported.
+type serviceSignal int
+
+const (
+	serviceStatus  = iota // Gets status about the service.
+	serviceRestart        // Restarts the service.
+	serviceStop           // Stops the server.
+	// Add new service requests here.
+)
+
+// Global service signal channel.
+var globalServiceSignalCh chan serviceSignal
+
+// Global service done channel.
+var globalServiceDoneCh chan struct{}
+
+// Initialize service mutex once.
+func init() {
+	globalServiceDoneCh = make(chan struct{}, 1)
+	globalServiceSignalCh = make(chan serviceSignal, 1)
+}
+
+// restartProcess starts a new process passing it the active fd's. It
+// doesn't fork, but starts a new process using the same environment and
+// arguments as when it was originally started. This allows for a newly
+// deployed binary to be started. It returns the pid of the newly started
+// process when successful.
+func restartProcess() error {
+	// Use the original binary location. This works with symlinks such that if
+	// the file it points to has been changed we will use the updated symlink.
+	argv0, err := exec.LookPath(os.Args[0])
+	if err != nil {
+		return err
+	}
+
+	// Pass on the environment and replace the old count key with the new one.
+	cmd := exec.Command(argv0, os.Args[1:]...)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	return cmd.Start()
+}
+
+// Handles all serviceSignal and execute service functions.
+func (m *ServerMux) handleServiceSignals() error {
+	// Custom exit function
+	runExitFn := func(err error) {
+		// If global profiler is set stop before we exit.
+		if globalProfiler != nil {
+			globalProfiler.Stop()
+		}
+
+		// Call user supplied user exit function
+		fatalIf(err, "Unable to gracefully complete service operation.")
+
+		// We are usually done here, close global service done channel.
+		globalServiceDoneCh <- struct{}{}
+	}
+
+	// Start listening on service signal. Monitor signals.
+	trapCh := signalTrap(os.Interrupt, syscall.SIGTERM)
+	for {
+		select {
+		case <-trapCh:
+			// Initiate graceful stop.
+			globalServiceSignalCh <- serviceStop
+		case signal := <-globalServiceSignalCh:
+			switch signal {
+			case serviceStatus:
+				/// We don't do anything for this.
+			case serviceRestart:
+				if err := m.Close(); err != nil {
+					errorIf(err, "Unable to close server gracefully")
+				}
+				if err := restartProcess(); err != nil {
+					errorIf(err, "Unable to restart the server.")
+				}
+				runExitFn(nil)
+			case serviceStop:
+				if err := m.Close(); err != nil {
+					errorIf(err, "Unable to close server gracefully")
+				}
+				objAPI := newObjectLayerFn()
+				if objAPI == nil {
+					// Server not initialized yet, exit happily.
+					runExitFn(nil)
+				}
+				runExitFn(objAPI.Shutdown())
+			}
+		}
+	}
+}