### Locks

We have 3 different things that we synchronize on.

#### Http2Connection

This lock guards internal state of each connection. This lock is never held for blocking operations. That means that we acquire the lock, read or write a few fields and release the lock. No I/O and no application-layer callbacks.

#### Http2Stream

   * be removed from the execution schedule.
   */
  fun cancelAll() {
    lock.assertNotHeld()

    taskRunner.lock.withLock {
      if (cancelAllAndDecide()) {
        taskRunner.kickCoordinator(this)
      }
    }
  }

  fun shutdown() {
    lock.assertNotHeld()

    taskRunner.lock.withLock {
      shutdown = true
      if (cancelAllAndDecide()) {

// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package cmd

import (
	"errors"
)

var (
	errLockConflict       = errors.New("lock conflict")
	errLockNotInitialized = errors.New("lock not initialized")
	errLockNotFound       = errors.New("lock not found")

func (m *metacacheManager) deleteBucketCache(bucket string) {
	m.init.Do(m.initManager)
	m.mu.Lock()
	b, ok := m.buckets[bucket]
	if !ok {
		m.mu.Unlock()
		return
	}
	delete(m.buckets, bucket)
	m.mu.Unlock()

	// Since deletes may take some time we try to do it without
	// holding lock to m all the time.
	b.mu.Lock()
	defer b.mu.Unlock()
	for k, v := range b.caches {

	var bytesWritten int64
	var bufs [][]byte
	for block := startBlock; block <= endBlock; block++ {
		var blockOffset, blockLength int64
		switch {
		case startBlock == endBlock:
			blockOffset = offset % e.blockSize
			blockLength = length
		case block == startBlock:
			blockOffset = offset % e.blockSize
			blockLength = e.blockSize - blockOffset
		case block == endBlock:
			blockOffset = 0

func (h *healSequence) getScannedItemsCount() int64 {
	var count int64
	h.mutex.RLock()
	defer h.mutex.RUnlock()

	for _, v := range h.scannedItemsMap {
		count += v
	}
	return count
}

// getScannedItemsMap - returns map of all scanned items against type
func (h *healSequence) getScannedItemsMap() map[madmin.HealItemType]int64 {
	h.mutex.RLock()
	defer h.mutex.RUnlock()

	// Make a copy before returning the value

	}
}

// Lock holds a write lock on dm.
//
// If the lock is already in use, the calling go routine
// blocks until the mutex is available.
func (dm *DRWMutex) Lock(id, source string) {
	isReadLock := false
	dm.lockBlocking(context.Background(), nil, id, source, isReadLock, Options{
		Timeout: drwMutexInfinite,
	})
}

// Options lock options.
type Options struct {

}

// List - returns available target IDs.
func (list *TargetList) List() []TargetID {
	list.RLock()
	defer list.RUnlock()

	keys := []TargetID{}
	for k := range list.targets {
		keys = append(keys, k)
	}

	return keys
}

func (list *TargetList) get(id TargetID) (Target, bool) {
	list.RLock()
	defer list.RUnlock()

	target, ok := list.targets[id]
	return target, ok
}

// Metadata has data stripped, if any.
func (s *xlStorage) WalkDir(ctx context.Context, opts WalkDirOptions, wr io.Writer) (err error) {
	legacyFS := !(s.fsType == xfs || s.fsType == ext4)

	s.RLock()
	legacy := s.formatLegacy
	s.RUnlock()

	// Verify if volume is valid and it exists.
	volumeDir, err := s.getVolDir(opts.Bucket)
	if err != nil {
		return err
	}

	if !skipAccessChecks(opts.Bucket) {

		time.Sleep(time.Duration(d))
	}

	l.mutex.Lock()
	defer l.mutex.Unlock()
	var locksHeld int64
	if locksHeld, reply = l.lockMap[args.Resources[0]]; !reply { // No lock is held on the given name
		return false, fmt.Errorf("RUnlock attempted on an unlocked entity: %s", args.Resources[0])
	}
	if reply = locksHeld != WriteLock; !reply { // A write-lock is held, cannot release a read lock