Merge pull request #1685 from AudriusButkevicius/mut

Add mutex logging

cmd/syncthing/gui.go

@@ -22,7 +22,6 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
-	"sync"
 	"time"
 
 	"github.com/calmh/logger"
@@ -34,6 +33,7 @@ import (
 	"github.com/syncthing/syncthing/internal/events"
 	"github.com/syncthing/syncthing/internal/model"
 	"github.com/syncthing/syncthing/internal/osutil"
+	"github.com/syncthing/syncthing/internal/sync"
 	"github.com/syncthing/syncthing/internal/upgrade"
 	"github.com/vitrun/qart/qr"
 	"golang.org/x/crypto/bcrypt"
@@ -45,16 +45,16 @@ type guiError struct {
 }
 
 var (
-	configInSync = true
-	guiErrors    = []guiError{}
-	guiErrorsMut sync.Mutex
-	startTime    = time.Now()
+	configInSync            = true
+	guiErrors               = []guiError{}
+	guiErrorsMut sync.Mutex = sync.NewMutex()
+	startTime               = time.Now()
 	eventSub     *events.BufferedSubscription
 )
 
 var (
 	lastEventRequest    time.Time
-	lastEventRequestMut sync.Mutex
+	lastEventRequestMut sync.Mutex = sync.NewMutex()
 )
 
 func startGUI(cfg config.GUIConfiguration, assetDir string, m *model.Model) error {
@@ -522,7 +522,7 @@ func flushResponse(s string, w http.ResponseWriter) {
 }
 
 var cpuUsagePercent [10]float64 // The last ten seconds
-var cpuUsageLock sync.RWMutex
+var cpuUsageLock sync.RWMutex = sync.NewRWMutex()
 
 func restGetSystemStatus(w http.ResponseWriter, r *http.Request) {
 	var m runtime.MemStats

cmd/syncthing/gui_auth.go

@@ -12,16 +12,16 @@ import (
 	"math/rand"
 	"net/http"
 	"strings"
-	"sync"
 	"time"
 
 	"github.com/syncthing/syncthing/internal/config"
+	"github.com/syncthing/syncthing/internal/sync"
 	"golang.org/x/crypto/bcrypt"
 )
 
 var (
-	sessions    = make(map[string]bool)
-	sessionsMut sync.Mutex
+	sessions               = make(map[string]bool)
+	sessionsMut sync.Mutex = sync.NewMutex()
 )
 
 func basicAuthAndSessionMiddleware(cfg config.GUIConfiguration, next http.Handler) http.Handler {

cmd/syncthing/gui_csrf.go

@@ -12,14 +12,14 @@ import (
 	"net/http"
 	"os"
 	"strings"
-	"sync"
 	"time"
 
 	"github.com/syncthing/syncthing/internal/osutil"
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 var csrfTokens []string
-var csrfMut sync.Mutex
+var csrfMut sync.Mutex = sync.NewMutex()
 
 // Check for CSRF token on /rest/ URLs. If a correct one is not given, reject
 // the request with 403. For / and /index.html, set a new CSRF cookie if none

cmd/syncthing/monitor.go

@@ -14,17 +14,17 @@ import (
 	"os/signal"
 	"runtime"
 	"strings"
-	"sync"
 	"syscall"
 	"time"
 
 	"github.com/syncthing/syncthing/internal/osutil"
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 var (
-	stdoutFirstLines []string // The first 10 lines of stdout
-	stdoutLastLines  []string // The last 50 lines of stdout
-	stdoutMut        sync.Mutex
+	stdoutFirstLines []string   // The first 10 lines of stdout
+	stdoutLastLines  []string   // The last 50 lines of stdout
+	stdoutMut        sync.Mutex = sync.NewMutex()
 )
 
 const (

cmd/syncthing/summarysvc.go

@@ -7,11 +7,11 @@
 package main
 
 import (
-	"sync"
 	"time"
 
 	"github.com/syncthing/syncthing/internal/events"
 	"github.com/syncthing/syncthing/internal/model"
+	"github.com/syncthing/syncthing/internal/sync"
 	"github.com/thejerf/suture"
 )
 
@@ -37,6 +37,7 @@ func (c *folderSummarySvc) Serve() {
 	c.stop = make(chan struct{})
 	c.folders = make(map[string]struct{})
 	c.srv = srv
+	c.foldersMut = sync.NewMutex()
 
 	srv.Serve()
 }

internal/config/wrapper.go

@@ -10,11 +10,11 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
-	"sync"
 
 	"github.com/syncthing/protocol"
 	"github.com/syncthing/syncthing/internal/events"
 	"github.com/syncthing/syncthing/internal/osutil"
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 // An interface to handle configuration changes, and a wrapper type á la
@@ -49,7 +49,12 @@ type Wrapper struct {
 // Wrap wraps an existing Configuration structure and ties it to a file on
 // disk.
 func Wrap(path string, cfg Configuration) *Wrapper {
-	w := &Wrapper{cfg: cfg, path: path}
+	w := &Wrapper{
+		cfg:  cfg,
+		path: path,
+		mut:  sync.NewMutex(),
+		sMut: sync.NewMutex(),
+	}
 	w.replaces = make(chan Configuration)
 	go w.Serve()
 	return w

internal/db/blockmap.go

@@ -17,11 +17,11 @@ import (
 	"bytes"
 	"encoding/binary"
 	"sort"
-	"sync"
 
 	"github.com/syncthing/protocol"
 	"github.com/syncthing/syncthing/internal/config"
 	"github.com/syncthing/syncthing/internal/osutil"
+	"github.com/syncthing/syncthing/internal/sync"
 
 	"github.com/syndtr/goleveldb/leveldb"
 	"github.com/syndtr/goleveldb/leveldb/util"
@@ -123,7 +123,8 @@ func NewBlockFinder(db *leveldb.DB, cfg *config.Wrapper) *BlockFinder {
 	}
 
 	f := &BlockFinder{
-		db: db,
+		db:  db,
+		mut: sync.NewRWMutex(),
 	}
 	f.Changed(cfg.Raw())
 	cfg.Subscribe(f)

internal/db/concurrency_test.go

@@ -10,10 +10,11 @@ import (
 	"crypto/rand"
 	"log"
 	"os"
-	"sync"
 	"testing"
 	"time"
 
+	"github.com/syncthing/syncthing/internal/sync"
+
 	"github.com/syndtr/goleveldb/leveldb"
 	"github.com/syndtr/goleveldb/leveldb/opt"
 	"github.com/syndtr/goleveldb/leveldb/util"
@@ -132,7 +133,7 @@ func TestConcurrentSetClear(t *testing.T) {
 
 	dur := 30 * time.Second
 	t0 := time.Now()
-	var wg sync.WaitGroup
+	wg := sync.NewWaitGroup()
 
 	os.RemoveAll("testdata/concurrent-set-clear.db")
 	db, err := leveldb.OpenFile("testdata/concurrent-set-clear.db", &opt.Options{OpenFilesCacheCapacity: 10})
@@ -188,7 +189,7 @@ func TestConcurrentSetOnly(t *testing.T) {
 
 	dur := 30 * time.Second
 	t0 := time.Now()
-	var wg sync.WaitGroup
+	wg := sync.NewWaitGroup()
 
 	os.RemoveAll("testdata/concurrent-set-only.db")
 	db, err := leveldb.OpenFile("testdata/concurrent-set-only.db", &opt.Options{OpenFilesCacheCapacity: 10})

internal/db/leveldb.go

@@ -14,9 +14,9 @@ import (
 	"fmt"
 	"runtime"
 	"sort"
-	"sync"
 
 	"github.com/syncthing/protocol"
+	"github.com/syncthing/syncthing/internal/sync"
 	"github.com/syndtr/goleveldb/leveldb"
 	"github.com/syndtr/goleveldb/leveldb/iterator"
 	"github.com/syndtr/goleveldb/leveldb/opt"
@@ -25,7 +25,7 @@ import (
 
 var (
 	clockTick int64
-	clockMut  sync.Mutex
+	clockMut  sync.Mutex = sync.NewMutex()
 )
 
 func clock(v int64) int64 {

internal/db/set.go

@@ -13,10 +13,9 @@
 package db
 
 import (
-	"sync"
-
 	"github.com/syncthing/protocol"
 	"github.com/syncthing/syncthing/internal/osutil"
+	"github.com/syncthing/syncthing/internal/sync"
 	"github.com/syndtr/goleveldb/leveldb"
 )
 
@@ -50,6 +49,7 @@ func NewFileSet(folder string, db *leveldb.DB) *FileSet {
 		folder:       folder,
 		db:           db,
 		blockmap:     NewBlockMap(db, folder),
+		mutex:        sync.NewMutex(),
 	}
 
 	ldbCheckGlobals(db, []byte(folder))

internal/discover/client_test.go

@@ -9,12 +9,13 @@ package discover
 import (
 	"fmt"
 	"net"
-	"sync"
 	"time"
 
 	"testing"
 
 	"github.com/syncthing/protocol"
+
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 var device protocol.DeviceID
@@ -97,7 +98,7 @@ func TestUDP4Success(t *testing.T) {
 
 	// Do a lookup in a separate routine
 	addrs := []string{}
-	wg := sync.WaitGroup{}
+	wg := sync.NewWaitGroup()
 	wg.Add(1)
 	go func() {
 		addrs = client.Lookup(device)
@@ -193,7 +194,7 @@ func TestUDP4Failure(t *testing.T) {
 
 	// Do a lookup in a separate routine
 	addrs := []string{}
-	wg := sync.WaitGroup{}
+	wg := sync.NewWaitGroup()
 	wg.Add(1)
 	go func() {
 		addrs = client.Lookup(device)

internal/discover/client_udp.go

@@ -12,16 +12,19 @@ import (
 	"net"
 	"net/url"
 	"strconv"
-	"sync"
 	"time"
 
 	"github.com/syncthing/protocol"
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 func init() {
 	for _, proto := range []string{"udp", "udp4", "udp6"} {
 		Register(proto, func(uri *url.URL, pkt *Announce) (Client, error) {
-			c := &UDPClient{}
+			c := &UDPClient{
+				wg:  sync.NewWaitGroup(),
+				mut: sync.NewRWMutex(),
+			}
 			err := c.Start(uri, pkt)
 			if err != nil {
 				return nil, err

internal/discover/discover.go

@@ -13,12 +13,12 @@ import (
 	"io"
 	"net"
 	"strconv"
-	"sync"
 	"time"
 
 	"github.com/syncthing/protocol"
 	"github.com/syncthing/syncthing/internal/beacon"
 	"github.com/syncthing/syncthing/internal/events"
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 type Discoverer struct {
@@ -59,6 +59,8 @@ func NewDiscoverer(id protocol.DeviceID, addresses []string) *Discoverer {
 		negCacheCutoff: 3 * time.Minute,
 		registry:       make(map[protocol.DeviceID][]CacheEntry),
 		lastLookup:     make(map[protocol.DeviceID]time.Time),
+		registryLock:   sync.NewRWMutex(),
+		mut:            sync.NewRWMutex(),
 	}
 }
 
@@ -140,7 +142,7 @@ func (d *Discoverer) StartGlobal(servers []string, extPort uint16) {
 
 	d.extPort = extPort
 	pkt := d.announcementPkt()
-	wg := sync.WaitGroup{}
+	wg := sync.NewWaitGroup()
 	clients := make(chan Client, len(servers))
 	for _, address := range servers {
 		wg.Add(1)
@@ -216,7 +218,7 @@ func (d *Discoverer) Lookup(device protocol.DeviceID) []string {
 		// server client and one local announcement interval has passed. This is
 		// to avoid finding local peers on their remote address at startup.
 		results := make(chan []string, len(d.clients))
-		wg := sync.WaitGroup{}
+		wg := sync.NewWaitGroup()
 		for _, client := range d.clients {
 			wg.Add(1)
 			go func(c Client) {

internal/events/events.go

@@ -9,8 +9,10 @@ package events
 
 import (
 	"errors"
-	"sync"
+	stdsync "sync"
 	"time"
+
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 type EventType int
@@ -113,7 +115,8 @@ var (
 
 func NewLogger() *Logger {
 	return &Logger{
-		subs: make(map[int]*Subscription),
+		subs:  make(map[int]*Subscription),
+		mutex: sync.NewMutex(),
 	}
 }
 
@@ -150,6 +153,7 @@ func (l *Logger) Subscribe(mask EventType) *Subscription {
 		mask:   mask,
 		id:     l.nextID,
 		events: make(chan Event, BufferSize),
+		mutex:  sync.NewMutex(),
 	}
 	l.nextID++
 	l.subs[s.id] = s
@@ -197,15 +201,16 @@ type BufferedSubscription struct {
 	next int
 	cur  int
 	mut  sync.Mutex
-	cond *sync.Cond
+	cond *stdsync.Cond
 }
 
 func NewBufferedSubscription(s *Subscription, size int) *BufferedSubscription {
 	bs := &BufferedSubscription{
 		sub: s,
 		buf: make([]Event, size),
+		mut: sync.NewMutex(),
 	}
-	bs.cond = sync.NewCond(&bs.mut)
+	bs.cond = stdsync.NewCond(bs.mut)
 	go bs.pollingLoop()
 	return bs
 }

internal/ignore/ignore.go

@@ -16,10 +16,10 @@ import (
 	"path/filepath"
 	"regexp"
 	"strings"
-	"sync"
 	"time"
 
 	"github.com/syncthing/syncthing/internal/fnmatch"
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 type Pattern struct {
@@ -48,6 +48,7 @@ func New(withCache bool) *Matcher {
 	m := &Matcher{
 		withCache: withCache,
 		stop:      make(chan struct{}),
+		mut:       sync.NewMutex(),
 	}
 	if withCache {
 		go m.clean(2 * time.Hour)

internal/model/deviceactivity.go

@@ -7,9 +7,8 @@
 package model
 
 import (
-	"sync"
-
 	"github.com/syncthing/protocol"
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 // deviceActivity tracks the number of outstanding requests per device and can
@@ -23,6 +22,7 @@ type deviceActivity struct {
 func newDeviceActivity() *deviceActivity {
 	return &deviceActivity{
 		act: make(map[protocol.DeviceID]int),
+		mut: sync.NewMutex(),
 	}
 }
 

internal/model/folderstate.go

@@ -7,10 +7,10 @@
 package model
 
 import (
-	"sync"
 	"time"
 
 	"github.com/syncthing/syncthing/internal/events"
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 type folderState int

internal/model/model.go

@@ -18,7 +18,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
-	"sync"
+	stdsync "sync"
 	"time"
 
 	"github.com/syncthing/protocol"
@@ -30,6 +30,7 @@ import (
 	"github.com/syncthing/syncthing/internal/scanner"
 	"github.com/syncthing/syncthing/internal/stats"
 	"github.com/syncthing/syncthing/internal/symlinks"
+	"github.com/syncthing/syncthing/internal/sync"
 	"github.com/syncthing/syncthing/internal/versioner"
 	"github.com/syndtr/goleveldb/leveldb"
 )
@@ -85,7 +86,7 @@ type Model struct {
 }
 
 var (
-	SymlinkWarning = sync.Once{}
+	SymlinkWarning = stdsync.Once{}
 )
 
 // NewModel creates and starts a new model. The model starts in read-only mode,
@@ -113,6 +114,9 @@ func NewModel(cfg *config.Wrapper, id protocol.DeviceID, deviceName, clientName,
 		protoConn:       make(map[protocol.DeviceID]protocol.Connection),
 		rawConn:         make(map[protocol.DeviceID]io.Closer),
 		deviceVer:       make(map[protocol.DeviceID]string),
+
+		fmut: sync.NewRWMutex(),
+		pmut: sync.NewRWMutex(),
 	}
 	if cfg.Options().ProgressUpdateIntervalS > -1 {
 		go m.progressEmitter.Serve()
@@ -125,8 +129,8 @@ func NewModel(cfg *config.Wrapper, id protocol.DeviceID, deviceName, clientName,
 // the locks cannot be acquired in the given timeout period.
 func (m *Model) StartDeadlockDetector(timeout time.Duration) {
 	l.Infof("Starting deadlock detector with %v timeout", timeout)
-	deadlockDetect(&m.fmut, timeout)
-	deadlockDetect(&m.pmut, timeout)
+	deadlockDetect(m.fmut, timeout)
+	deadlockDetect(m.pmut, timeout)
 }
 
 // StartRW starts read/write processing on the current model. When in
@@ -1099,9 +1103,9 @@ func (m *Model) ScanFolders() map[string]error {
 	m.fmut.RUnlock()
 
 	errors := make(map[string]error, len(m.folderCfgs))
-	var errorsMut sync.Mutex
+	errorsMut := sync.NewMutex()
 
-	var wg sync.WaitGroup
+	wg := sync.NewWaitGroup()
 	wg.Add(len(folders))
 	for _, folder := range folders {
 		folder := folder

internal/model/progressemitter.go

@@ -9,11 +9,11 @@ package model
 import (
 	"path/filepath"
 	"reflect"
-	"sync"
 	"time"
 
 	"github.com/syncthing/syncthing/internal/config"
 	"github.com/syncthing/syncthing/internal/events"
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 type ProgressEmitter struct {
@@ -35,6 +35,7 @@ func NewProgressEmitter(cfg *config.Wrapper) *ProgressEmitter {
 		registry: make(map[string]*sharedPullerState),
 		last:     make(map[string]map[string]*pullerProgress),
 		timer:    time.NewTimer(time.Millisecond),
+		mut:      sync.NewMutex(),
 	}
 	t.Changed(cfg.Raw())
 	cfg.Subscribe(t)

internal/model/progressemitter_test.go

@@ -12,6 +12,7 @@ import (
 
 	"github.com/syncthing/syncthing/internal/config"
 	"github.com/syncthing/syncthing/internal/events"
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 var timeout = 10 * time.Millisecond
@@ -50,7 +51,9 @@ func TestProgressEmitter(t *testing.T) {
 
 	expectTimeout(w, t)
 
-	s := sharedPullerState{}
+	s := sharedPullerState{
+		mut: sync.NewMutex(),
+	}
 	p.Register(&s)
 
 	expectEvent(w, t, 1)

internal/model/queue.go

@@ -6,7 +6,7 @@
 
 package model
 
-import "sync"
+import "github.com/syncthing/syncthing/internal/sync"
 
 type jobQueue struct {
 	progress []string
@@ -15,7 +15,9 @@ type jobQueue struct {
 }
 
 func newJobQueue() *jobQueue {
-	return &jobQueue{}
+	return &jobQueue{
+		mut: sync.NewMutex(),
+	}
 }
 
 func (q *jobQueue) Push(file string) {

internal/model/rofolder.go

@@ -10,6 +10,8 @@ import (
 	"fmt"
 	"math/rand"
 	"time"
+
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 type roFolder struct {
@@ -23,11 +25,14 @@ type roFolder struct {
 
 func newROFolder(model *Model, folder string, interval time.Duration) *roFolder {
 	return &roFolder{
-		stateTracker: stateTracker{folder: folder},
-		folder:       folder,
-		intv:         interval,
-		model:        model,
-		stop:         make(chan struct{}),
+		stateTracker: stateTracker{
+			folder: folder,
+			mut:    sync.NewMutex(),
+		},
+		folder: folder,
+		intv:   interval,
+		model:  model,
+		stop:   make(chan struct{}),
 	}
 }
 

internal/model/rwfolder.go

@@ -13,7 +13,6 @@ import (
 	"math/rand"
 	"os"
 	"path/filepath"
-	"sync"
 	"time"
 
 	"github.com/syncthing/protocol"
@@ -24,6 +23,7 @@ import (
 	"github.com/syncthing/syncthing/internal/osutil"
 	"github.com/syncthing/syncthing/internal/scanner"
 	"github.com/syncthing/syncthing/internal/symlinks"
+	"github.com/syncthing/syncthing/internal/sync"
 	"github.com/syncthing/syncthing/internal/versioner"
 )
 
@@ -77,7 +77,10 @@ type rwFolder struct {
 
 func newRWFolder(m *Model, shortID uint64, cfg config.FolderConfiguration) *rwFolder {
 	return &rwFolder{
-		stateTracker: stateTracker{folder: cfg.ID},
+		stateTracker: stateTracker{
+			folder: cfg.ID,
+			mut:    sync.NewMutex(),
+		},
 
 		model:           m,
 		progressEmitter: m.progressEmitter,
@@ -279,10 +282,10 @@ func (p *rwFolder) pullerIteration(ignores *ignore.Matcher) int {
 	copyChan := make(chan copyBlocksState)
 	finisherChan := make(chan *sharedPullerState)
 
-	var updateWg sync.WaitGroup
-	var copyWg sync.WaitGroup
-	var pullWg sync.WaitGroup
-	var doneWg sync.WaitGroup
+	updateWg := sync.NewWaitGroup()
+	copyWg := sync.NewWaitGroup()
+	pullWg := sync.NewWaitGroup()
+	doneWg := sync.NewWaitGroup()
 
 	if debug {
 		l.Debugln(p, "c", p.copiers, "p", p.pullers)
@@ -799,6 +802,7 @@ func (p *rwFolder) handleFile(file protocol.FileInfo, copyChan chan<- copyBlocks
 		reused:      reused,
 		ignorePerms: p.ignorePerms,
 		version:     curFile.Version,
+		mut:         sync.NewMutex(),
 	}
 
 	if debug {

internal/model/sharedpullerstate.go

@@ -10,10 +10,10 @@ import (
 	"io"
 	"os"
 	"path/filepath"
-	"sync"
 
 	"github.com/syncthing/protocol"
 	"github.com/syncthing/syncthing/internal/db"
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 // A sharedPullerState is kept for each file that is being synced and is kept
@@ -59,8 +59,8 @@ type lockedWriterAt struct {
 }
 
 func (w lockedWriterAt) WriteAt(p []byte, off int64) (n int, err error) {
-	w.mut.Lock()
-	defer w.mut.Unlock()
+	(*w.mut).Lock()
+	defer (*w.mut).Unlock()
 	return w.wr.WriteAt(p, off)
 }
 

internal/model/sharedpullerstate_test.go

@@ -9,11 +9,14 @@ package model
 import (
 	"os"
 	"testing"
+
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 func TestSourceFileOK(t *testing.T) {
 	s := sharedPullerState{
 		realName: "testdata/foo",
+		mut:      sync.NewMutex(),
 	}
 
 	fd, err := s.sourceFile()
@@ -42,6 +45,7 @@ func TestSourceFileOK(t *testing.T) {
 func TestSourceFileBad(t *testing.T) {
 	s := sharedPullerState{
 		realName: "nonexistent",
+		mut:      sync.NewMutex(),
 	}
 
 	fd, err := s.sourceFile()
@@ -67,6 +71,7 @@ func TestReadOnlyDir(t *testing.T) {
 
 	s := sharedPullerState{
 		tempName: "testdata/read_only_dir/.temp_name",
+		mut:      sync.NewMutex(),
 	}
 
 	fd, err := s.tempFile()

internal/osutil/osutil.go

@@ -15,14 +15,15 @@ import (
 	"path/filepath"
 	"runtime"
 	"strings"
-	"sync"
+
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 var ErrNoHome = errors.New("No home directory found - set $HOME (or the platform equivalent).")
 
 // Try to keep this entire operation atomic-like. We shouldn't be doing this
 // often enough that there is any contention on this lock.
-var renameLock sync.Mutex
+var renameLock sync.Mutex = sync.NewMutex()
 
 // TryRename renames a file, leaving source file intact in case of failure.
 // Tries hard to succeed on various systems by temporarily tweaking directory

internal/scanner/blockqueue.go

@@ -9,9 +9,9 @@ package scanner
 import (
 	"os"
 	"path/filepath"
-	"sync"
 
 	"github.com/syncthing/protocol"
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 // The parallell hasher reads FileInfo structures from the inbox, hashes the
@@ -20,7 +20,7 @@ import (
 // is closed and all items handled.
 
 func newParallelHasher(dir string, blockSize, workers int, outbox, inbox chan protocol.FileInfo) {
-	var wg sync.WaitGroup
+	wg := sync.NewWaitGroup()
 	wg.Add(workers)
 
 	for i := 0; i < workers; i++ {

internal/sync/debug.go

@@ -0,0 +1,31 @@
+// Copyright (C) 2015 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package sync
+
+import (
+	"os"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/calmh/logger"
+)
+
+var (
+	debug     = strings.Contains(os.Getenv("STTRACE"), "locks") || os.Getenv("STTRACE") == "all"
+	threshold = time.Duration(100 * time.Millisecond)
+	l         = logger.DefaultLogger
+)
+
+func init() {
+	if n, err := strconv.Atoi(os.Getenv("STLOCKTHRESHOLD")); debug && err == nil {
+		threshold = time.Duration(n) * time.Millisecond
+	}
+	if debug {
+		l.Debugf("Enabling lock logging at %v threshold", threshold)
+	}
+}

internal/sync/sync.go

@@ -0,0 +1,144 @@
+// Copyright (C) 2015 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package sync
+
+import (
+	"fmt"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+type Mutex interface {
+	Lock()
+	Unlock()
+}
+
+type RWMutex interface {
+	Mutex
+	RLock()
+	RUnlock()
+}
+
+type WaitGroup interface {
+	Add(int)
+	Done()
+	Wait()
+}
+
+func NewMutex() Mutex {
+	if debug {
+		return &loggedMutex{}
+	}
+	return &sync.Mutex{}
+}
+
+func NewRWMutex() RWMutex {
+	if debug {
+		return &loggedRWMutex{
+			unlockers: make([]string, 0),
+		}
+	}
+	return &sync.RWMutex{}
+}
+
+func NewWaitGroup() WaitGroup {
+	if debug {
+		return &loggedWaitGroup{}
+	}
+	return &sync.WaitGroup{}
+}
+
+type loggedMutex struct {
+	sync.Mutex
+	start    time.Time
+	lockedAt string
+}
+
+func (m *loggedMutex) Lock() {
+	m.Mutex.Lock()
+	m.start = time.Now()
+	m.lockedAt = getCaller()
+}
+
+func (m *loggedMutex) Unlock() {
+	duration := time.Now().Sub(m.start)
+	if duration >= threshold {
+		l.Debugf("Mutex held for %v. Locked at %s unlocked at %s", duration, m.lockedAt, getCaller())
+	}
+	m.Mutex.Unlock()
+}
+
+type loggedRWMutex struct {
+	sync.RWMutex
+	start    time.Time
+	lockedAt string
+
+	logUnlockers uint32
+
+	unlockers    []string
+	unlockersMut sync.Mutex
+}
+
+func (m *loggedRWMutex) Lock() {
+	start := time.Now()
+
+	atomic.StoreUint32(&m.logUnlockers, 1)
+	m.RWMutex.Lock()
+	m.logUnlockers = 0
+
+	m.start = time.Now()
+	duration := m.start.Sub(start)
+
+	m.lockedAt = getCaller()
+	if duration > threshold {
+		l.Debugf("RWMutex took %v to lock. Locked at %s. RUnlockers while locking: %s", duration, m.lockedAt, strings.Join(m.unlockers, ", "))
+	}
+	m.unlockers = m.unlockers[0:]
+}
+
+func (m *loggedRWMutex) Unlock() {
+	duration := time.Now().Sub(m.start)
+	if duration >= threshold {
+		l.Debugf("RWMutex held for %v. Locked at %s: unlocked at %s", duration, m.lockedAt, getCaller())
+	}
+	m.RWMutex.Unlock()
+}
+
+func (m *loggedRWMutex) RUnlock() {
+	if atomic.LoadUint32(&m.logUnlockers) == 1 {
+		m.unlockersMut.Lock()
+		m.unlockers = append(m.unlockers, getCaller())
+		m.unlockersMut.Unlock()
+	}
+	m.RWMutex.RUnlock()
+}
+
+type loggedWaitGroup struct {
+	sync.WaitGroup
+}
+
+func (wg *loggedWaitGroup) Done() {
+	start := time.Now()
+	wg.WaitGroup.Done()
+	duration := time.Now().Sub(start)
+	if duration > threshold {
+		l.Debugf("WaitGroup took %v at %s", duration, getCaller())
+	}
+}
+
+func getCaller() string {
+	pc := make([]uintptr, 10)
+	runtime.Callers(3, pc)
+	f := runtime.FuncForPC(pc[0])
+	file, line := f.FileLine(pc[0])
+	file = filepath.Join(filepath.Base(filepath.Dir(file)), filepath.Base(file))
+	return fmt.Sprintf("%s:%d", file, line)
+}

internal/upnp/upnp.go

@@ -22,8 +22,9 @@ import (
 	"net/url"
 	"regexp"
 	"strings"
-	"sync"
 	"time"
+
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 // A container for relevant properties of a UPnP InternetGatewayDevice.
@@ -129,7 +130,7 @@ func Discover(timeout time.Duration) []IGD {
 		}
 	}()
 
-	var wg sync.WaitGroup
+	wg := sync.NewWaitGroup()
 	for _, intf := range interfaces {
 		for _, deviceType := range []string{"urn:schemas-upnp-org:device:InternetGatewayDevice:1", "urn:schemas-upnp-org:device:InternetGatewayDevice:2"} {
 			wg.Add(1)

internal/versioner/staggered.go

@@ -11,10 +11,10 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
-	"sync"
 	"time"
 
 	"github.com/syncthing/syncthing/internal/osutil"
+	"github.com/syncthing/syncthing/internal/sync"
 )
 
 func init() {
@@ -33,7 +33,7 @@ type Staggered struct {
 	cleanInterval int64
 	folderPath    string
 	interval      [4]Interval
-	mutex         *sync.Mutex
+	mutex         sync.Mutex
 }
 
 // Rename versions with old version format
@@ -87,7 +87,6 @@ func NewStaggered(folderID, folderPath string, params map[string]string) Version
 		versionsDir = params["versionsPath"]
 	}
 
-	var mutex sync.Mutex
 	s := Staggered{
 		versionsPath:  versionsDir,
 		cleanInterval: cleanInterval,
@@ -98,7 +97,7 @@ func NewStaggered(folderID, folderPath string, params map[string]string) Version
 			{86400, 592000},  // next 30 days -> 1 day between versions
 			{604800, maxAge}, // next year -> 1 week between versions
 		},
-		mutex: &mutex,
+		mutex: sync.NewMutex(),
 	}
 
 	if debug {