69 lines
1.1 KiB
Go
69 lines
1.1 KiB
Go
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package storage
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import (
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"sync"
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)
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const (
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maxIndex = ^uint(0) // Max unit value
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)
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type (
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// Counter is responsible for operating queue read and write indexes
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counter struct {
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write uint // Number of the record last written to the queue
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read uint // Number of the record last read from the queue
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// If write index is greater than read index then there are unread messages
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// If write index is less tham read index then max index was reached
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mutex sync.Mutex
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stream chan uint
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streaming *sync.Cond
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}
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)
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func newCounter(wi, ri uint) (c *counter) {
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m := &sync.Mutex{}
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m.Lock()
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c = &counter{
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write: wi,
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read: ri,
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stream: make(chan uint),
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streaming: sync.NewCond(m),
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}
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go c.increment()
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return
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}
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func (c *counter) tryWrite(fn func(i uint) bool) {
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c.mutex.Lock()
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defer c.mutex.Unlock()
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if ok := fn(c.write + 1); ok {
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c.write++
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c.streaming.Signal()
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}
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}
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func (c *counter) distance() uint {
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d := c.write - c.read
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if d < 0 {
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d += maxIndex
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}
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return d
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}
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func (c *counter) increment() {
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for {
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if c.distance() == 0 {
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c.streaming.Wait()
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}
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c.stream <- c.read + 1
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c.read++
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}
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}
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