227 lines
6.1 KiB
Go
227 lines
6.1 KiB
Go
/*
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* Minio Cloud Storage, (C) 2016 Minio, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package cmd
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import (
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"context"
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"os"
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pathutil "path"
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"sync"
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"github.com/minio/minio/cmd/logger"
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"github.com/minio/minio/pkg/lock"
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)
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// fsIOPool represents a protected list to keep track of all
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// the concurrent readers at a given path.
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type fsIOPool struct {
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sync.Mutex
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readersMap map[string]*lock.RLockedFile
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}
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// lookupToRead - looks up an fd from readers map and
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// returns read locked fd for caller to read from, if
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// fd found increments the reference count. If the fd
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// is found to be closed then purges it from the
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// readersMap and returns nil instead.
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//
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// NOTE: this function is not protected and it is callers
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// responsibility to lock this call to be thread safe. For
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// implementation ideas look at the usage inside Open() call.
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func (fsi *fsIOPool) lookupToRead(path string) (*lock.RLockedFile, bool) {
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rlkFile, ok := fsi.readersMap[path]
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// File reference exists on map, validate if its
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// really closed and we are safe to purge it.
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if ok && rlkFile != nil {
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// If the file is closed and not removed from map is a bug.
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if rlkFile.IsClosed() {
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// Log this as an error.
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reqInfo := (&logger.ReqInfo{}).AppendTags("path", path)
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ctx := logger.SetReqInfo(context.Background(), reqInfo)
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logger.LogIf(ctx, errUnexpected)
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// Purge the cached lock path from map.
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delete(fsi.readersMap, path)
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// Indicate that we can populate the new fd.
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ok = false
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} else {
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// Increment the lock ref, since the file is not closed yet
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// and caller requested to read the file again.
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rlkFile.IncLockRef()
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}
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}
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return rlkFile, ok
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}
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// Open is a wrapper call to read locked file which
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// returns a ReadAtCloser.
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//
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// ReaderAt is provided so that the fd is non seekable, since
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// we are sharing fd's with concurrent threads, we don't want
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// all readers to change offsets on each other during such
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// concurrent operations. Using ReadAt allows us to read from
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// any offsets.
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//
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// Closer is implemented to track total readers and to close
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// only when there no more readers, the fd is purged if the lock
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// count has reached zero.
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func (fsi *fsIOPool) Open(path string) (*lock.RLockedFile, error) {
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if err := checkPathLength(path); err != nil {
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return nil, err
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}
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fsi.Lock()
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rlkFile, ok := fsi.lookupToRead(path)
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fsi.Unlock()
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// Locked path reference doesn't exist, acquire a read lock again on the file.
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if !ok {
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// Open file for reading with read lock.
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newRlkFile, err := lock.RLockedOpenFile(path)
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if err != nil {
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switch {
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case os.IsNotExist(err):
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return nil, errFileNotFound
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case os.IsPermission(err):
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return nil, errFileAccessDenied
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case isSysErrIsDir(err):
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return nil, errIsNotRegular
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case isSysErrNotDir(err):
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return nil, errFileAccessDenied
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case isSysErrPathNotFound(err):
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return nil, errFileNotFound
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default:
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return nil, err
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}
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}
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/// Save new reader on the map.
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// It is possible by this time due to concurrent
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// i/o we might have another lock present. Lookup
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// again to check for such a possibility. If no such
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// file exists save the newly opened fd, if not
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// reuse the existing fd and close the newly opened
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// file
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fsi.Lock()
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rlkFile, ok = fsi.lookupToRead(path)
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if ok {
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// Close the new fd, since we already seem to have
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// an active reference.
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newRlkFile.Close()
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} else {
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// Save the new rlk file.
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rlkFile = newRlkFile
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}
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// Save the new fd on the map.
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fsi.readersMap[path] = rlkFile
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fsi.Unlock()
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}
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// Success.
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return rlkFile, nil
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}
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// Write - Attempt to lock the file if it exists,
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// - if the file exists. Then we try to get a write lock this
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// will block if we can't get a lock perhaps another write
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// or read is in progress. Concurrent calls are protected
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// by the global namspace lock within the same process.
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func (fsi *fsIOPool) Write(path string) (wlk *lock.LockedFile, err error) {
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if err = checkPathLength(path); err != nil {
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return nil, err
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}
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wlk, err = lock.LockedOpenFile(path, os.O_RDWR, 0666)
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if err != nil {
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switch {
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case os.IsNotExist(err):
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return nil, errFileNotFound
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case os.IsPermission(err):
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return nil, errFileAccessDenied
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case isSysErrIsDir(err):
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return nil, errIsNotRegular
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default:
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return nil, err
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}
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}
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return wlk, nil
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}
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// Create - creates a new write locked file instance.
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// - if the file doesn't exist. We create the file and hold lock.
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func (fsi *fsIOPool) Create(path string) (wlk *lock.LockedFile, err error) {
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if err = checkPathLength(path); err != nil {
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return nil, err
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}
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// Creates parent if missing.
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if err = mkdirAll(pathutil.Dir(path), 0777); err != nil {
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return nil, err
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}
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// Attempt to create the file.
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wlk, err = lock.LockedOpenFile(path, os.O_RDWR|os.O_CREATE, 0666)
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if err != nil {
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switch {
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case os.IsPermission(err):
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return nil, errFileAccessDenied
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case isSysErrIsDir(err):
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return nil, errIsNotRegular
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case isSysErrPathNotFound(err):
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return nil, errFileAccessDenied
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default:
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return nil, err
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}
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}
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// Success.
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return wlk, nil
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}
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// Close implements closing the path referenced by the reader in such
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// a way that it makes sure to remove entry from the map immediately
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// if no active readers are present.
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func (fsi *fsIOPool) Close(path string) error {
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fsi.Lock()
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defer fsi.Unlock()
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if err := checkPathLength(path); err != nil {
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return err
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}
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// Pop readers from path.
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rlkFile, ok := fsi.readersMap[path]
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if !ok {
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return nil
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}
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// Close the reader.
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rlkFile.Close()
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// If the file is closed, remove it from the reader pool map.
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if rlkFile.IsClosed() {
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// Purge the cached lock path from map.
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delete(fsi.readersMap, path)
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}
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// Success.
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return nil
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}
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