tidb hack 代码
文件路径：/util/hack/hack.go
/ Copyright 2015 PingCAP, Inc.
/
/ Licensed under the Apache License, Version 2.0 (the "License");
/ you may not use this file except in compliance with the License.
/ You may obtain a copy of the License at
/
/ http://www.apache.org/licenses/LICENSE-2.0
/
/ Unless required by applicable law or agreed to in writing, software
/ distributed under the License is distributed on an "AS IS" BASIS,
/ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/ See the License for the specific language governing permissions and
/ limitations under the License.
package hack
import (
"reflect"
"unsafe"
)
/ MutableString can be used as string via string(MutableString) without performance loss.
type MutableString string
/ String converts slice to MutableString without copy.
/ The MutableString can be converts to string without copy.
/ Use it at your own risk.
func String(b []byte) (s MutableString) {
if len(b) == 0 {
return ""
}
pbytes := (*reflect.SliceHeader)(unsafe.Pointer(&b))
pstring := (*reflect.StringHeader)(unsafe.Pointer(&s))
pstring.Data = pbytes.Data
pstring.Len = pbytes.Len
return s
}
/ Slice converts string to slice without copy.
/ Use at your own risk.
func Slice(s string) (b []byte) {
pbytes := (*reflect.SliceHeader)(unsafe.Pointer(&b))
pstring := (*reflect.StringHeader)(unsafe.Pointer(&s))
pbytes.Data = pstring.Data
pbytes.Len = pstring.Len
pbytes.Cap = pstring.Len
return b
}
/ LoadFactor is the maximum average load of a bucket that triggers growth is 6.5 in Golang Map.
/ Represent as LoadFactorNum/LoadFactorDen, to allow integer math.
/ They are from the golang definition. ref: https://github.com/golang/go/blob/go1.13.15/src/runtime/map.go#L68-L71
const (
/ LoadFactorNum is the numerator of load factor
LoadFactorNum = 13
/ LoadFactorDen is the denominator of load factor
LoadFactorDen = 2
)
const (
/ DefBucketMemoryUsageForMapStrToSlice = bucketSize*(1+unsafe.Sizeof(string) + unsafe.Sizeof(slice))+2*ptrSize
/ ref https://github.com/golang/go/blob/go1.15.6/src/reflect/type.go#L2162.
/ The bucket size may be changed by golang implement in the future.
/ Golang Map needs to acquire double the memory when expanding, and the old buckets will be released after the data is migrated.
/ Considering the worst case, the data in the old bucket cannot be migrated in time, and the old bucket cannot
/ be GCed, we expand the bucket size to 1.5 times to estimate the memory usage of Golang Map.
DefBucketMemoryUsageForMapStrToSlice = (8*(1+16+24) + 16) / 2 * 3
/ DefBucketMemoryUsageForMapIntToPtr = bucketSize*(1+unsafe.Sizeof(uint64) + unsafe.Sizeof(pointer))+2*ptrSize
DefBucketMemoryUsageForMapIntToPtr = (8*(1+8+8) + 16) / 2 * 3
/ DefBucketMemoryUsageForMapStringToAny = bucketSize*(1+unsafe.Sizeof(string) + unsafe.Sizeof(interface{}))+2*ptrSize
DefBucketMemoryUsageForMapStringToAny = (8*(1+16+16) + 16) / 2 * 3
/ DefBucketMemoryUsageForSetString = bucketSize*(1+unsafe.Sizeof(string) + unsafe.Sizeof(struct{}))+2*ptrSize
DefBucketMemoryUsageForSetString = (8*(1+16+0) + 16) / 2 * 3
/ DefBucketMemoryUsageForSetFloat64 = bucketSize*(1+unsafe.Sizeof(float64) + unsafe.Sizeof(struct{}))+2*ptrSize
DefBucketMemoryUsageForSetFloat64 = (8*(1+8+0) + 16) / 2 * 3
/ DefBucketMemoryUsageForSetInt64 = bucketSize*(1+unsafe.Sizeof(int64) + unsafe.Sizeof(struct{}))+2*ptrSize
DefBucketMemoryUsageForSetInt64 = (8*(1+8+0) + 16) / 2 * 3
)
/ EstimateBucketMemoryUsage returns the estimated memory usage of a bucket in a map.
func EstimateBucketMemoryUsage[K comparable, V any]() uint64 {
return (8*(1+uint64(unsafe.Sizeof(*new(K))+unsafe.Sizeof(*new(V)))) + 16) / 2 * 3
}