74 lines
2.0 KiB
Go
74 lines
2.0 KiB
Go
// Package memorylocker provides an in-memory locking mechanism.
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//
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// When multiple processes are attempting to access an upload, whether it be
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// by reading or writing, a synchronization mechanism is required to prevent
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// data corruption, especially to ensure correct offset values and the proper
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// order of chunks inside a single upload.
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//
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// MemoryLocker persists locks using memory and therefore allowing a simple and
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// cheap mechanism. Locks will only exist as long as this object is kept in
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// reference and will be erased if the program exits.
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package memorylocker
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import (
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"sync"
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"github.com/tus/tusd/pkg/handler"
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)
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// MemoryLocker persists locks using memory and therefore allowing a simple and
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// cheap mechanism. Locks will only exist as long as this object is kept in
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// reference and will be erased if the program exits.
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type MemoryLocker struct {
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locks map[string]struct{}
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mutex sync.Mutex
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}
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// New creates a new in-memory locker.
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func New() *MemoryLocker {
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return &MemoryLocker{
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locks: make(map[string]struct{}),
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}
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}
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// UseIn adds this locker to the passed composer.
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func (locker *MemoryLocker) UseIn(composer *handler.StoreComposer) {
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composer.UseLocker(locker)
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}
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func (locker *MemoryLocker) NewLock(id string) (handler.Lock, error) {
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return memoryLock{locker, id}, nil
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}
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type memoryLock struct {
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locker *MemoryLocker
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id string
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}
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// Lock tries to obtain the exclusive lock.
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func (lock memoryLock) Lock() error {
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lock.locker.mutex.Lock()
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defer lock.locker.mutex.Unlock()
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// Ensure file is not locked
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if _, ok := lock.locker.locks[lock.id]; ok {
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return handler.ErrFileLocked
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}
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lock.locker.locks[lock.id] = struct{}{}
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return nil
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}
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// Unlock releases a lock. If no such lock exists, no error will be returned.
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func (lock memoryLock) Unlock() error {
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lock.locker.mutex.Lock()
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// Deleting a non-existing key does not end in unexpected errors or panic
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// since this operation results in a no-op
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delete(lock.locker.locks, lock.id)
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lock.locker.mutex.Unlock()
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return nil
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}
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