Add Graceful shutdown for Windows and hooks for shutdown of goroutines (#8964)

* Graceful Shutdown for windows and others

Restructures modules/graceful, adding shutdown for windows, removing and
replacing the old minwinsvc code.

Creates a new waitGroup - terminate which allows for goroutines to
finish up after the shutdown of the servers.

Shutdown and terminate hooks are added for goroutines.

* Remove unused functions - these can be added in a different PR

* Add startup timeout functionality

* Document STARTUP_TIMEOUT

modules/graceful/restart_unix.go

@@ -0,0 +1,81 @@
+// +build !windows
+
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+// This code is heavily inspired by the archived gofacebook/gracenet/net.go handler
+
+package graceful
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+	"sync"
+	"syscall"
+)
+
+var killParent sync.Once
+
+// KillParent sends the kill signal to the parent process if we are a child
+func KillParent() {
+	killParent.Do(func() {
+		if Manager.IsChild() {
+			ppid := syscall.Getppid()
+			if ppid > 1 {
+				_ = syscall.Kill(ppid, syscall.SIGTERM)
+			}
+		}
+	})
+}
+
+// RestartProcess starts a new process passing it the active listeners. 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() (int, error) {
+	listeners := getActiveListeners()
+
+	// Extract the fds from the listeners.
+	files := make([]*os.File, len(listeners))
+	for i, l := range listeners {
+		var err error
+		// Now, all our listeners actually have File() functions so instead of
+		// individually casting we just use a hacky interface
+		files[i], err = l.(filer).File()
+		if err != nil {
+			return 0, err
+		}
+		// Remember to close these at the end.
+		defer files[i].Close()
+	}
+
+	// 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 0, err
+	}
+
+	// Pass on the environment and replace the old count key with the new one.
+	var env []string
+	for _, v := range os.Environ() {
+		if !strings.HasPrefix(v, listenFDs+"=") {
+			env = append(env, v)
+		}
+	}
+	env = append(env, fmt.Sprintf("%s=%d", listenFDs, len(listeners)))
+
+	allFiles := append([]*os.File{os.Stdin, os.Stdout, os.Stderr}, files...)
+	process, err := os.StartProcess(argv0, os.Args, &os.ProcAttr{
+		Dir:   originalWD,
+		Env:   env,
+		Files: allFiles,
+	})
+	if err != nil {
+		return 0, err
+	}
+	return process.Pid, nil
+}