// Singleton contains a pointer to T that must be set once.
// Until the value is set all Get() calls will block.
type Singleton[T any] struct {
	v   *T
	set chan struct{}
}

// NewSingleton creates a new unset singleton.
func NewSingleton[T any]() *Singleton[T] {
	return &Singleton[T]{set: make(chan struct{}), v: nil}
}

// Get will return the singleton value.
func (s *Singleton[T]) Get() *T {
	<-s.set
	return s.v
}

	}
	f.(*fileWriter).crc32 = fakeHash32{}
	chunk := make([]byte, chunkSize)
	for i := range chunk {
		chunk[i] = '.'
	}
	for i := 0; i < chunks; i++ {
		_, err := f.Write(chunk)
		if err != nil {
			t.Fatal("write chunk:", err)
		}
	}
	if frag := int(size % chunkSize); frag > 0 {
		_, err := f.Write(chunk[:frag])
		if err != nil {
			t.Fatal("write chunk:", err)
		}
	}
	end := []byte("END\n")

		// not be required but makes reproduction much easier.
		nsLk.lockMapMutex.Lock()

		// lk3 blocks.
		lk3ch := make(chan bool)
		go func() {
			lk3ch <- nsLk.lock(ctx, "volume", "path", "source", "opsID", false, 0)
		}()

		// lk4, blocks.
		lk4ch := make(chan bool)
		go func() {
			lk4ch <- nsLk.lock(ctx, "volume", "path", "source", "opsID", false, 0)
		}()
		runtime.Gosched()

	saver := z.serverPools[o.pool].sets[o.set]

	// Disconnect from call above, but cancel on exit.
	listCtx, cancel := context.WithCancel(GlobalContext)
	saveCh := make(chan metaCacheEntry, metacacheBlockSize)
	inCh := make(chan metaCacheEntry, metacacheBlockSize)
	outCh := make(chan metaCacheEntry, o.Limit)

	filteredResults := o.gatherResults(ctx, outCh)

	mc := o.newMetacache()

		// Register a single handler which echos the payload.
		errFatal(remote.RegisterStreamingHandler(handlerTest, StreamHandler{
			// Send 10x response.
			Handle: func(ctx context.Context, payload []byte, _ <-chan []byte, out chan<- []byte) *RemoteErr {
				for i := 0; i < responses; i++ {
					toSend := GetByteBuffer()[:0]
					toSend = append(toSend, byte(i))
					toSend = append(toSend, payload...)
					select {

	retry := false
	for attempts := 1; attempts <= retryAttempts; attempts++ {
		attempts := attempts
		var (
			walkCh = make(chan itemOrErr[ObjectInfo], 100)
			slowCh = make(chan itemOrErr[ObjectInfo], 100)
		)

		if r.Source.Snowball.Disable != nil && !*r.Source.Snowball.Disable && r.Source.Type.isMinio() && r.Target.Type.isMinio() {
			go func() {

// Updates are sent on a regular basis and the caller *must* consume them.
func (er erasureObjects) nsScanner(ctx context.Context, buckets []BucketInfo, wantCycle uint32, updates chan<- dataUsageCache, healScanMode madmin.HealScanMode) error {
	if len(buckets) == 0 {
		return nil
	}

	// Collect disks we can use.
	disks, healing := er.getOnlineDisksWithHealing(false)
	if len(disks) == 0 {

var ErrBatchFull = errors.New("batch is full")

const defaultCommitTimeout = 30 * time.Second

// Batch represents an ordered batch
type Batch[I any] struct {
	items  []I
	limit  uint32
	store  Store[I]
	quitCh chan struct{}

	sync.Mutex
}

// BatchConfig represents the batch config
type BatchConfig[I any] struct {
	Limit         uint32
	Store         Store[I]
	CommitTimeout time.Duration
	Log           logger
}

	if !s.checkID(params.DiskID) {
		return grid.NewRemoteErr(errDiskNotFound)
	}
	if params.Cache == nil {
		return grid.NewRemoteErrString("NSScannerHandler: provided cache is nil")
	}

	// Collect updates, stream them before the full cache is sent.
	updates := make(chan dataUsageEntry, 1)
	var wg sync.WaitGroup
	wg.Add(1)

)

var sharedLockTimeout = newDynamicTimeoutWithOpts(dynamicTimeoutOpts{
	timeout:       30 * time.Second,
	minimum:       10 * time.Second,
	retryInterval: time.Minute,
})

type sharedLock struct {
	lockContext chan LockContext
}

func (ld sharedLock) backgroundRoutine(ctx context.Context, objAPI ObjectLayer, lockName string) {
	for {
		locker := objAPI.NewNSLock(minioMetaBucket, lockName)