72 lines
1.6 KiB
Go
72 lines
1.6 KiB
Go
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package NumGen
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import (
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"time"
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)
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// Function to generate a unique ID.
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func GetUniqueID() (id int64) {
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// Exklusive access:
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genLock.Lock()
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defer genLock.Unlock()
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incremented := false
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Retry:
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// Read the current time
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t1 := time.Now().UTC()
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t1Milliseconds := int(float64(t1.Nanosecond()) / 1000000.0)
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// Calculate the difference to the last generated number:
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diff := t1.Sub(genCurrentTime)
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// Case 1: Huge difference?
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if diff.Seconds() > 1.0 {
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genCurrentTime = t1
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genCurrentMillisecond = t1Milliseconds
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genCurrentMillisecondCounter = 0
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id = generateUniqueID(genCurrentMillisecondCounter)
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return
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}
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/*
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The fist case is necessary, because the same count of milliseconds
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can occur every second, etc. ;-) Therefore, a check only by the
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milliseconds is not sufficient.
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*/
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// Case 2: Small difference?
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if t1Milliseconds != genCurrentMillisecond {
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genCurrentTime = t1
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genCurrentMillisecond = t1Milliseconds
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genCurrentMillisecondCounter = 0
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id = generateUniqueID(genCurrentMillisecondCounter)
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return
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}
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//
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// Case 3: Another number must be generated at the same millisecond!
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//
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if incremented == false {
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genCurrentMillisecondCounter++
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incremented = true
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}
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// Case 3.1: More than 1000 numbers are generated at one millisecond?
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if genCurrentMillisecondCounter > 999 {
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// This is not possible with the current algorithm!
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// Therefore, we force this and all other request to wait some time:
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time.Sleep(1 * time.Millisecond)
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// Try it again:
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goto Retry
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// Case 3.2: Less than 1000 numbers are generated at one millisecond?
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} else {
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// This case is fine:
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id = generateUniqueID(genCurrentMillisecondCounter)
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return
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}
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}
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