88 lines
1.6 KiB
Go
88 lines
1.6 KiB
Go
// Copyright © 2016 Abcum Ltd
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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 db
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import (
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"context"
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"fmt"
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"sync"
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"sync/atomic"
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)
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type mutex struct {
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m sync.Map
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}
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type value struct {
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v uint32
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q chan struct{}
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l chan struct{}
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}
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func (m *mutex) Lock(ctx context.Context, key fmt.Stringer) {
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_, v := m.item(ctx, key)
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select {
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case <-ctx.Done():
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return
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case <-v.q:
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return
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case v.l <- struct{}{}:
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atomic.StoreUint32(&v.v, vers(ctx))
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return
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default:
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if atomic.LoadUint32(&v.v) < vers(ctx) {
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close(v.q)
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panic(errRaceCondition)
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}
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}
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select {
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case <-ctx.Done():
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return
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case <-v.q:
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return
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case v.l <- struct{}{}:
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atomic.StoreUint32(&v.v, vers(ctx))
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return
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}
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}
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func (m *mutex) Unlock(ctx context.Context, key fmt.Stringer) {
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_, v := m.item(ctx, key)
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select {
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case <-ctx.Done():
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return
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case <-v.q:
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return
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case <-v.l:
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return
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}
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}
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func (m *mutex) item(ctx context.Context, key fmt.Stringer) (string, *value) {
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k := key.String()
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v, _ := m.m.LoadOrStore(k, &value{
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v: vers(ctx),
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q: make(chan struct{}),
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l: make(chan struct{}, 1),
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})
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return k, v.(*value)
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}
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