rename all remaining packages to internal/ (#12418)

This is to ensure that there are no projects
that try to import `minio/minio/pkg` into
their own repo. Any such common packages should
go to `https://github.com/minio/pkg`

internal/lock/lock.go

@@ -0,0 +1,102 @@
+// Copyright (c) 2015-2021 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+// Package lock - implements filesystem locking wrappers around an
+// open file descriptor.
+package lock
+
+import (
+	"errors"
+	"os"
+	"sync"
+)
+
+var (
+	// ErrAlreadyLocked is returned if the underlying fd is already locked.
+	ErrAlreadyLocked = errors.New("file already locked")
+)
+
+// RLockedFile represents a read locked file, implements a special
+// closer which only closes the associated *os.File when the ref count.
+// has reached zero, i.e when all the readers have given up their locks.
+type RLockedFile struct {
+	*LockedFile
+	mutex sync.Mutex
+	refs  int // Holds read lock refs.
+}
+
+// IsClosed - Check if the rlocked file is already closed.
+func (r *RLockedFile) IsClosed() bool {
+	r.mutex.Lock()
+	defer r.mutex.Unlock()
+	return r.refs == 0
+}
+
+// IncLockRef - is used by called to indicate lock refs.
+func (r *RLockedFile) IncLockRef() {
+	r.mutex.Lock()
+	r.refs++
+	r.mutex.Unlock()
+}
+
+// Close - this closer implements a special closer
+// closes the underlying fd only when the refs
+// reach zero.
+func (r *RLockedFile) Close() (err error) {
+	r.mutex.Lock()
+	defer r.mutex.Unlock()
+
+	if r.refs == 0 {
+		return os.ErrInvalid
+	}
+
+	r.refs--
+	if r.refs == 0 {
+		err = r.File.Close()
+	}
+
+	return err
+}
+
+// Provides a new initialized read locked struct from *os.File
+func newRLockedFile(lkFile *LockedFile) (*RLockedFile, error) {
+	if lkFile == nil {
+		return nil, os.ErrInvalid
+	}
+
+	return &RLockedFile{
+		LockedFile: lkFile,
+		refs:       1,
+	}, nil
+}
+
+// RLockedOpenFile - returns a wrapped read locked file, if the file
+// doesn't exist at path returns an error.
+func RLockedOpenFile(path string) (*RLockedFile, error) {
+	lkFile, err := LockedOpenFile(path, os.O_RDONLY, 0666)
+	if err != nil {
+		return nil, err
+	}
+
+	return newRLockedFile(lkFile)
+
+}
+
+// LockedFile represents a locked file
+type LockedFile struct {
+	*os.File
+}