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70 lines
2 KiB
Go
70 lines
2 KiB
Go
// Copyright 2016 The Gogs Authors. All rights reserved.
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// Use of this source code is governed by a MIT-style
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// license that can be found in the LICENSE file.
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package sync
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import (
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"sync"
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)
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// ExclusivePool is a pool of non-identical instances
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// that only one instance with same identity is in the pool at a time.
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// In other words, only instances with different identities can be in
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// the pool the same time. If another instance with same identity tries
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// to get into the pool, it hangs until previous instance left the pool.
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//
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// This pool is particularly useful for performing tasks on same resource
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// on the file system in different goroutines.
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type ExclusivePool struct {
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lock sync.Mutex
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// pool maintains locks for each instance in the pool.
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pool map[string]*sync.Mutex
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// count maintains the number of times an instance with same identity checks in
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// to the pool, and should be reduced to 0 (removed from map) by checking out
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// with same number of times.
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// The purpose of count is to delete lock when count down to 0 and recycle memory
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// from map object.
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count map[string]int
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}
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// NewExclusivePool initializes and returns a new ExclusivePool object.
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func NewExclusivePool() *ExclusivePool {
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return &ExclusivePool{
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pool: make(map[string]*sync.Mutex),
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count: make(map[string]int),
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}
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}
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// CheckIn checks in an instance to the pool and hangs while instance
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// with same identity is using the lock.
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func (p *ExclusivePool) CheckIn(identity string) {
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p.lock.Lock()
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lock, has := p.pool[identity]
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if !has {
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lock = &sync.Mutex{}
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p.pool[identity] = lock
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}
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p.count[identity]++
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p.lock.Unlock()
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lock.Lock()
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}
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// CheckOut checks out an instance from the pool and releases the lock
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// to let other instances with same identity to grab the lock.
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func (p *ExclusivePool) CheckOut(identity string) {
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p.lock.Lock()
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defer p.lock.Unlock()
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p.pool[identity].Unlock()
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if p.count[identity] == 1 {
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delete(p.pool, identity)
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delete(p.count, identity)
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} else {
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p.count[identity]--
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}
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}
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