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// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause
package syncs
import (
"encoding/json"
"strconv"
"sync/atomic"
"golang.org/x/sys/cpu"
)
// ShardedInt provides a sharded atomic int64 value that optimizes high
// frequency (Mhz range and above) writes in highly parallel workloads.
// The zero value is not safe for use; use [NewShardedInt].
// ShardedInt implements the expvar.Var interface.
type ShardedInt struct {
sv *ShardValue[intShard]
}
// NewShardedInt returns a new [ShardedInt].
func NewShardedInt() *ShardedInt {
return &ShardedInt{
sv: NewShardValue[intShard](),
}
}
// Add adds delta to the value.
func (m *ShardedInt) Add(delta int64) {
m.sv.One(func(v *intShard) {
v.Add(delta)
})
}
type intShard struct {
atomic.Int64
_ cpu.CacheLinePad // avoid false sharing of neighboring shards
}
// Value returns the current value.
func (m *ShardedInt) Value() int64 {
var v int64
for s := range m.sv.All {
v += s.Load()
}
return v
}
// GetDistribution returns the current value in each shard.
// This is intended for observability/debugging only.
func (m *ShardedInt) GetDistribution() []int64 {
v := make([]int64, 0, m.sv.Len())
for s := range m.sv.All {
v = append(v, s.Load())
}
return v
}
// String implements the expvar.Var interface
func (m *ShardedInt) String() string {
v, _ := json.Marshal(m.Value())
return string(v)
}
// AppendText implements the encoding.TextAppender interface
func (m *ShardedInt) AppendText(b []byte) ([]byte, error) {
return strconv.AppendInt(b, m.Value(), 10), nil
}
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