106 lines
2.0 KiB
Go
106 lines
2.0 KiB
Go
/*
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Copyright The containerd Authors.
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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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http://www.apache.org/licenses/LICENSE-2.0
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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 kmutex provides synchronization primitives to lock/unlock resource by unique key.
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package kmutex
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import (
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"context"
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"fmt"
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"sync"
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"golang.org/x/sync/semaphore"
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)
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// KeyedLocker is the interface for acquiring locks based on string.
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type KeyedLocker interface {
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Lock(ctx context.Context, key string) error
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Unlock(key string)
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}
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func New() KeyedLocker {
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return newKeyMutex()
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}
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func newKeyMutex() *keyMutex {
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return &keyMutex{
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locks: make(map[string]*klock),
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}
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}
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type keyMutex struct {
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mu sync.Mutex
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locks map[string]*klock
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}
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type klock struct {
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*semaphore.Weighted
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ref int
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}
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func (km *keyMutex) Lock(ctx context.Context, key string) error {
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km.mu.Lock()
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l, ok := km.locks[key]
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if !ok {
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km.locks[key] = &klock{
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Weighted: semaphore.NewWeighted(1),
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}
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l = km.locks[key]
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}
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l.ref++
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km.mu.Unlock()
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if err := l.Acquire(ctx, 1); err != nil {
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km.mu.Lock()
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defer km.mu.Unlock()
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l.ref--
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if l.ref < 0 {
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panic(fmt.Errorf("kmutex: release of unlocked key %v", key))
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}
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if l.ref == 0 {
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delete(km.locks, key)
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}
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return err
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}
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return nil
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}
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func (km *keyMutex) Unlock(key string) {
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km.mu.Lock()
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defer km.mu.Unlock()
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l, ok := km.locks[key]
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if !ok {
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panic(fmt.Errorf("kmutex: unlock of unlocked key %v", key))
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}
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l.Release(1)
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l.ref--
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if l.ref < 0 {
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panic(fmt.Errorf("kmutex: released of unlocked key %v", key))
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}
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if l.ref == 0 {
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delete(km.locks, key)
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}
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}
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