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/net_unix.go

@@ -0,0 +1,211 @@
+// +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"
+	"net"
+	"os"
+	"strconv"
+	"strings"
+	"sync"
+
+	"code.gitea.io/gitea/modules/log"
+)
+
+const (
+	listenFDs = "LISTEN_FDS"
+	startFD   = 3
+)
+
+// In order to keep the working directory the same as when we started we record
+// it at startup.
+var originalWD, _ = os.Getwd()
+
+var (
+	once  = sync.Once{}
+	mutex = sync.Mutex{}
+
+	providedListeners = []net.Listener{}
+	activeListeners   = []net.Listener{}
+)
+
+func getProvidedFDs() (savedErr error) {
+	// Only inherit the provided FDS once but we will save the error so that repeated calls to this function will return the same error
+	once.Do(func() {
+		mutex.Lock()
+		defer mutex.Unlock()
+
+		numFDs := os.Getenv(listenFDs)
+		if numFDs == "" {
+			return
+		}
+		n, err := strconv.Atoi(numFDs)
+		if err != nil {
+			savedErr = fmt.Errorf("%s is not a number: %s. Err: %v", listenFDs, numFDs, err)
+			return
+		}
+
+		for i := startFD; i < n+startFD; i++ {
+			file := os.NewFile(uintptr(i), fmt.Sprintf("listener_FD%d", i))
+
+			l, err := net.FileListener(file)
+			if err == nil {
+				// Close the inherited file if it's a listener
+				if err = file.Close(); err != nil {
+					savedErr = fmt.Errorf("error closing provided socket fd %d: %s", i, err)
+					return
+				}
+				providedListeners = append(providedListeners, l)
+				continue
+			}
+
+			// If needed we can handle packetconns here.
+			savedErr = fmt.Errorf("Error getting provided socket fd %d: %v", i, err)
+			return
+		}
+	})
+	return savedErr
+}
+
+// CloseProvidedListeners closes all unused provided listeners.
+func CloseProvidedListeners() error {
+	mutex.Lock()
+	defer mutex.Unlock()
+	var returnableError error
+	for _, l := range providedListeners {
+		err := l.Close()
+		if err != nil {
+			log.Error("Error in closing unused provided listener: %v", err)
+			if returnableError != nil {
+				returnableError = fmt.Errorf("%v & %v", returnableError, err)
+			} else {
+				returnableError = err
+			}
+		}
+	}
+	providedListeners = []net.Listener{}
+
+	return returnableError
+}
+
+// GetListener obtains a listener for the local network address. The network must be
+// a stream-oriented network: "tcp", "tcp4", "tcp6", "unix" or "unixpacket". It
+// returns an provided net.Listener for the matching network and address, or
+// creates a new one using net.Listen.
+func GetListener(network, address string) (net.Listener, error) {
+	// Add a deferral to say that we've tried to grab a listener
+	defer Manager.InformCleanup()
+	switch network {
+	case "tcp", "tcp4", "tcp6":
+		tcpAddr, err := net.ResolveTCPAddr(network, address)
+		if err != nil {
+			return nil, err
+		}
+		return GetListenerTCP(network, tcpAddr)
+	case "unix", "unixpacket":
+		unixAddr, err := net.ResolveUnixAddr(network, address)
+		if err != nil {
+			return nil, err
+		}
+		return GetListenerUnix(network, unixAddr)
+	default:
+		return nil, net.UnknownNetworkError(network)
+	}
+}
+
+// GetListenerTCP announces on the local network address. The network must be:
+// "tcp", "tcp4" or "tcp6". It returns a provided net.Listener for the
+// matching network and address, or creates a new one using net.ListenTCP.
+func GetListenerTCP(network string, address *net.TCPAddr) (*net.TCPListener, error) {
+	if err := getProvidedFDs(); err != nil {
+		return nil, err
+	}
+
+	mutex.Lock()
+	defer mutex.Unlock()
+
+	// look for a provided listener
+	for i, l := range providedListeners {
+		if isSameAddr(l.Addr(), address) {
+			providedListeners = append(providedListeners[:i], providedListeners[i+1:]...)
+
+			activeListeners = append(activeListeners, l)
+			return l.(*net.TCPListener), nil
+		}
+	}
+
+	// no provided listener for this address -> make a fresh listener
+	l, err := net.ListenTCP(network, address)
+	if err != nil {
+		return nil, err
+	}
+	activeListeners = append(activeListeners, l)
+	return l, nil
+}
+
+// GetListenerUnix announces on the local network address. The network must be:
+// "unix" or "unixpacket". It returns a provided net.Listener for the
+// matching network and address, or creates a new one using net.ListenUnix.
+func GetListenerUnix(network string, address *net.UnixAddr) (*net.UnixListener, error) {
+	if err := getProvidedFDs(); err != nil {
+		return nil, err
+	}
+
+	mutex.Lock()
+	defer mutex.Unlock()
+
+	// look for a provided listener
+	for i, l := range providedListeners {
+		if isSameAddr(l.Addr(), address) {
+			providedListeners = append(providedListeners[:i], providedListeners[i+1:]...)
+			activeListeners = append(activeListeners, l)
+			return l.(*net.UnixListener), nil
+		}
+	}
+
+	// make a fresh listener
+	l, err := net.ListenUnix(network, address)
+	if err != nil {
+		return nil, err
+	}
+	activeListeners = append(activeListeners, l)
+	return l, nil
+}
+
+func isSameAddr(a1, a2 net.Addr) bool {
+	// If the addresses are not on the same network fail.
+	if a1.Network() != a2.Network() {
+		return false
+	}
+
+	// If the two addresses have the same string representation they're equal
+	a1s := a1.String()
+	a2s := a2.String()
+	if a1s == a2s {
+		return true
+	}
+
+	// This allows for ipv6 vs ipv4 local addresses to compare as equal. This
+	// scenario is common when listening on localhost.
+	const ipv6prefix = "[::]"
+	a1s = strings.TrimPrefix(a1s, ipv6prefix)
+	a2s = strings.TrimPrefix(a2s, ipv6prefix)
+	const ipv4prefix = "0.0.0.0"
+	a1s = strings.TrimPrefix(a1s, ipv4prefix)
+	a2s = strings.TrimPrefix(a2s, ipv4prefix)
+	return a1s == a2s
+}
+
+func getActiveListeners() []net.Listener {
+	mutex.Lock()
+	defer mutex.Unlock()
+	listeners := make([]net.Listener, len(activeListeners))
+	copy(listeners, activeListeners)
+	return listeners
+}