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Lock-free snowflake-like id generator in Golang
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package main | |
import ( | |
"fmt" | |
"os" | |
"sync" | |
"sync/atomic" | |
"time" | |
) | |
func main() { | |
g := &IdGenerator{worker: 0} | |
var wg sync.WaitGroup | |
var sm sync.Map | |
count := 10000 | |
for i := 0; i < count; i++ { | |
wg.Add(1) | |
go func() { | |
defer wg.Done() | |
id := g.NewID() | |
if _, loaded := sm.LoadOrStore(id, true); loaded { | |
fmt.Fprintf(os.Stderr, "id conflict: %v\n", id) | |
} | |
}() | |
} | |
wg.Wait() | |
var smsize int | |
sm.Range(func(_, _ interface{}) bool { smsize++; return true }) | |
if count != smsize { | |
fmt.Fprintf(os.Stderr, "%v %v\n", count, smsize) | |
os.Exit(1) | |
} | |
} | |
type IdGenerator struct { | |
worker, last uint64 | |
} | |
func (g *IdGenerator) NewID() uint64 { | |
const ( | |
seqbits = 12 | |
workerbits = 10 | |
timeoffset = workerbits + seqbits | |
basetime = 1640995200000 // time.Date(2022, 1, 1, 0, 0, 0, 0, time.UTC).UnixMilli() | |
) | |
var now, sequence uint64 | |
var d time.Duration | |
for { | |
now = uint64(time.Now().UnixMilli()) - basetime | |
last := atomic.AddUint64(&g.last, 1) | |
if old := last >> timeoffset; old == now { | |
// If the timestamps are identical and sequence is acceptable, use it. | |
if sequence = last & (1<<timeoffset - 1); sequence <= 1<<seqbits-1 { | |
break | |
} | |
if sequence > 1<<(seqbits+2) { | |
// Try to set sequence to the maximum to avoid overflow. | |
atomic.CompareAndSwapUint64(&g.last, last, now<<timeoffset|1<<seqbits-1) | |
} | |
// No more sequence in this timestamp is available so sleep for a bit. | |
time.Sleep(100 * time.Microsecond) | |
} else if old < now { | |
// The timestamp is updated so reset the sequence. | |
if atomic.CompareAndSwapUint64(&g.last, last, now<<timeoffset) { | |
// If saving the new sequence is accepted, use it. | |
sequence = 0 | |
break | |
} | |
} else { | |
// Newer timestamp is set by different goroutine, sequence overflow, or clock rewind. | |
if d == 0 { | |
d = 100 * time.Microsecond | |
} else if d *= 2; d >= time.Second { | |
// Clock rewind happened, unlikely to able to generate a new sequence so give up. | |
panic("IdGenerator.NewID: clock rewind") | |
} | |
time.Sleep(d) | |
} | |
} | |
v := now<<timeoffset | g.worker<<seqbits | sequence | |
fmt.Printf("%d\t%d\t%d\t%4d\n", v, now, g.worker, sequence) // for debugging | |
return v | |
} |
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