Add lock conflict check

lock.go

@@ -52,6 +52,8 @@ func NewExclusiveLock(repo *repository.Repository) (*Lock, error) {
 	return newLock(repo, true)
 }
 
+const waitBeforeLockCheck = 200 * time.Millisecond
+
 func newLock(repo *repository.Repository, excl bool) (*Lock, error) {
 	lock := &Lock{
 		Time:      time.Now(),
@@ -78,6 +80,13 @@ func newLock(repo *repository.Repository, excl bool) (*Lock, error) {
 		return nil, err
 	}
 
+	time.Sleep(waitBeforeLockCheck)
+
+	if err = lock.checkForOtherLocks(); err != nil {
+		lock.Unlock()
+		return nil, ErrAlreadyLocked
+	}
+
 	return lock, nil
 }
 
@@ -111,6 +120,10 @@ func (l *Lock) fillUserInfo() error {
 // exclusive lock is found.
 func (l *Lock) checkForOtherLocks() error {
 	return eachLock(l.repo, func(id backend.ID, lock *Lock, err error) error {
+		if id.Equal(l.lockID) {
+			return nil
+		}
+
 		// ignore locks that cannot be loaded
 		if err != nil {
 			return nil

lock_test.go

@@ -2,6 +2,7 @@ package restic_test
 
 import (
 	"os"
+	"sync"
 	"testing"
 	"time"
 
@@ -168,3 +169,79 @@ func TestLockWithStaleLock(t *testing.T) {
 
 	OK(t, removeLock(repo, id2))
 }
+
+func TestLockConflictingExclusiveLocks(t *testing.T) {
+	repo := SetupRepo()
+	defer TeardownRepo(repo)
+
+	for _, jobs := range []int{5, 23, 200} {
+		var wg sync.WaitGroup
+		errch := make(chan error, jobs)
+
+		f := func() {
+			defer wg.Done()
+
+			lock, err := restic.NewExclusiveLock(repo)
+			errch <- err
+			OK(t, lock.Unlock())
+		}
+
+		for i := 0; i < jobs; i++ {
+			wg.Add(1)
+			go f()
+		}
+
+		errors := 0
+		for i := 0; i < jobs; i++ {
+			err := <-errch
+			if err != nil {
+				errors++
+			}
+		}
+
+		wg.Wait()
+
+		Assert(t, errors == jobs-1,
+			"Expected %d errors, got %d", jobs-1, errors)
+	}
+}
+
+func TestLockConflictingLocks(t *testing.T) {
+	repo := SetupRepo()
+	defer TeardownRepo(repo)
+
+	var wg sync.WaitGroup
+
+	errch := make(chan error, 2)
+
+	wg.Add(2)
+
+	go func() {
+		defer wg.Done()
+
+		lock, err := restic.NewExclusiveLock(repo)
+		errch <- err
+		OK(t, lock.Unlock())
+	}()
+
+	go func() {
+		defer wg.Done()
+
+		lock, err := restic.NewLock(repo)
+		errch <- err
+		OK(t, lock.Unlock())
+	}()
+
+	errors := 0
+	for i := 0; i < 2; i++ {
+		err := <-errch
+		if err != nil {
+			errors++
+		}
+	}
+
+	wg.Wait()
+
+	Assert(t, errors == 1,
+		"Expected exactly one errors, got %d", errors)
+}