wehub-resource-sync
121 lines
3.0 KiB
Go
121 lines
3.0 KiB
Go
// Copyright 2019 Dolthub, 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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package filesys
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import (
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"errors"
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"sync/atomic"
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"github.com/dolthub/fslock"
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)
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const unlockedStateValue int32 = 0
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const lockedStateValue int32 = 1
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// errLockUnlock occurs if there is an error unlocking the lock
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var errLockUnlock = errors.New("unable to unlock the lock")
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// FilesysLock is an interface for locking and unlocking filesystems
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type FilesysLock interface {
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TryLock() (bool, error)
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Unlock() error
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}
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// CreateFilesysLock creates a new FilesysLock
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func CreateFilesysLock(fs Filesys, filename string) FilesysLock {
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switch fs.(type) {
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case *InMemFS:
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return NewInMemFileLock(fs)
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case *localFS:
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return NewLocalFileLock(fs, filename)
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default:
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panic("Unsupported file system")
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}
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}
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// InMemFileLock is a lock for the InMemFS
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type InMemFileLock struct {
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state int32
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}
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// NewInMemFileLock creates a new InMemFileLock
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func NewInMemFileLock(fs Filesys) *InMemFileLock {
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return &InMemFileLock{unlockedStateValue}
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}
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// TryLock attempts to lock the lock or fails if it is already locked
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func (memLock *InMemFileLock) TryLock() (bool, error) {
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if atomic.CompareAndSwapInt32(&memLock.state, unlockedStateValue, lockedStateValue) {
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return true, nil
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}
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return false, nil
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}
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// Unlock unlocks the lock
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func (memLock *InMemFileLock) Unlock() error {
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if memLock.state == 0 {
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return nil
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}
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new := atomic.AddInt32(&memLock.state, -lockedStateValue)
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if new != 0 {
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return errLockUnlock
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}
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return nil
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}
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// LocalFileLock is the lock for the localFS
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type LocalFileLock struct {
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filename string
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lck *fslock.Lock
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}
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// NewLocalFileLock creates a new LocalFileLock
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func NewLocalFileLock(fs Filesys, filename string) *LocalFileLock {
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return &LocalFileLock{filename: filename}
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}
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// TryLock attempts to lock the lock or fails if it is already locked. The
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// underlying fslock holds a directory handle for as long as it exists, so the
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// lock is created here and released in Unlock; this keeps the handle open only
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// while the lock is held.
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func (locLock *LocalFileLock) TryLock() (bool, error) {
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lck, err := fslock.New(locLock.filename)
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if err != nil {
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return false, err
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}
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if err := lck.TryLock(); err != nil {
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_ = lck.Close()
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return false, err
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}
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locLock.lck = lck
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return true, nil
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}
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// Unlock unlocks the lock and releases the underlying directory handle
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func (locLock *LocalFileLock) Unlock() error {
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if locLock.lck == nil {
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return nil
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}
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err := locLock.lck.Unlock()
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if cerr := locLock.lck.Close(); err == nil {
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err = cerr
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}
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locLock.lck = nil
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return err
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}
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