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72 lines
1.9 KiB
72 lines
1.9 KiB
// Copyright 2014, Google Inc. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package pools
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import (
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"fmt"
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"sync"
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)
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// IDPool is used to ensure that the set of IDs in use concurrently never
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// contains any duplicates. The IDs start at 1 and increase without bound, but
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// will never be larger than the peak number of concurrent uses.
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//
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// IDPool's Get() and Set() methods can be used concurrently.
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type IDPool struct {
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sync.Mutex
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// used holds the set of values that have been returned to us with Put().
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used map[uint32]bool
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// maxUsed remembers the largest value we've given out.
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maxUsed uint32
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}
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// NewIDPool creates and initializes an IDPool.
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func NewIDPool() *IDPool {
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return &IDPool{
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used: make(map[uint32]bool),
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}
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}
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// Get returns an ID that is unique among currently active users of this pool.
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func (pool *IDPool) Get() (id uint32) {
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pool.Lock()
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defer pool.Unlock()
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// Pick a value that's been returned, if any.
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for key, _ := range pool.used {
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delete(pool.used, key)
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return key
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}
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// No recycled IDs are available, so increase the pool size.
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pool.maxUsed += 1
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return pool.maxUsed
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}
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// Put recycles an ID back into the pool for others to use. Putting back a value
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// or 0, or a value that is not currently "checked out", will result in a panic
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// because that should never happen except in the case of a programming error.
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func (pool *IDPool) Put(id uint32) {
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pool.Lock()
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defer pool.Unlock()
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if id < 1 || id > pool.maxUsed {
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panic(fmt.Errorf("IDPool.Put(%v): invalid value, must be in the range [1,%v]", id, pool.maxUsed))
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}
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if pool.used[id] {
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panic(fmt.Errorf("IDPool.Put(%v): can't put value that was already recycled", id))
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}
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// If we're recycling maxUsed, just shrink the pool.
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if id == pool.maxUsed {
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pool.maxUsed = id - 1
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return
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}
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// Add it to the set of recycled IDs.
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pool.used[id] = true
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}
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