91 lines
3.8 KiB
Go
91 lines
3.8 KiB
Go
// Copyright 2015 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package hack
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import (
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"runtime"
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"strings"
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"unsafe"
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)
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// MutableString can be used as string via string(MutableString) without performance loss.
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type MutableString string
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// String converts slice to MutableString without copy.
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// The MutableString can be converts to string without copy.
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// Use it at your own risk.
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func String(b []byte) MutableString {
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if len(b) == 0 {
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return ""
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}
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return MutableString(unsafe.String(unsafe.SliceData(b), len(b)))
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}
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// Slice converts string to slice without copy.
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// Use at your own risk.
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func Slice(s string) []byte {
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return unsafe.Slice(unsafe.StringData(s), len(s))
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}
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// LoadFactor is the maximum average load of a bucket that triggers growth is 6.5 in Golang Map.
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// Represent as LoadFactorNum/LoadFactorDen, to allow integer math.
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// They are from the golang definition. ref: https://github.com/golang/go/blob/go1.13.15/src/runtime/map.go#L68-L71
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const (
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// LoadFactorDen is the denominator of load factor
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LoadFactorDen = 2
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)
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// LoadFactorNum is the numerator of load factor
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var LoadFactorNum = 13
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func init() {
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// In go1.21, the load factor num becomes 12 and go team has decided not to backport the fix to 1.21.
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// See more details in https://github.com/golang/go/issues/63438
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if strings.Contains(runtime.Version(), `go1.21`) {
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LoadFactorNum = 12
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}
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}
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const (
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// DefBucketMemoryUsageForMapStrToSlice = bucketSize*(1+unsafe.Sizeof(string) + unsafe.Sizeof(slice))+2*ptrSize
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// ref https://github.com/golang/go/blob/go1.15.6/src/reflect/type.go#L2162.
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// The bucket size may be changed by golang implement in the future.
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// Golang Map needs to acquire double the memory when expanding,
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// and the old buckets will be released after the data is migrated.
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// Considering the worst case, the data in the old bucket cannot be migrated in time, and the old bucket cannot
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// be GCed, we expand the bucket size to 1.5 times to estimate the memory usage of Golang Map.
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DefBucketMemoryUsageForMapStrToSlice = (8*(1+16+24) + 16) / 2 * 3
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// DefBucketMemoryUsageForMapIntToPtr = bucketSize*(1+unsafe.Sizeof(uint64) + unsafe.Sizeof(pointer))+2*ptrSize
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DefBucketMemoryUsageForMapIntToPtr = (8*(1+8+8) + 16) / 2 * 3
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// DefBucketMemoryUsageForMapStringToAny = bucketSize*(1+unsafe.Sizeof(string) + unsafe.Sizeof(interface{}))+2*ptrSize
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DefBucketMemoryUsageForMapStringToAny = (8*(1+16+16) + 16) / 2 * 3
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// DefBucketMemoryUsageForSetString = bucketSize*(1+unsafe.Sizeof(string) + unsafe.Sizeof(struct{}))+2*ptrSize
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DefBucketMemoryUsageForSetString = (8*(1+16+0) + 16) / 2 * 3
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// DefBucketMemoryUsageForSetFloat64 = bucketSize*(1+unsafe.Sizeof(float64) + unsafe.Sizeof(struct{}))+2*ptrSize
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DefBucketMemoryUsageForSetFloat64 = (8*(1+8+0) + 16) / 2 * 3
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// DefBucketMemoryUsageForSetInt64 = bucketSize*(1+unsafe.Sizeof(int64) + unsafe.Sizeof(struct{}))+2*ptrSize
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DefBucketMemoryUsageForSetInt64 = (8*(1+8+0) + 16) / 2 * 3
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)
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// EstimateBucketMemoryUsage returns the estimated memory usage of a bucket in a map.
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func EstimateBucketMemoryUsage[K comparable, V any]() uint64 {
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return (8*(1+uint64(unsafe.Sizeof(*new(K))+unsafe.Sizeof(*new(V)))) + 16) / 2 * 3
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}
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// GetBytesFromPtr return a bytes array from the given ptr and length
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func GetBytesFromPtr(ptr unsafe.Pointer, length int) []byte {
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return unsafe.Slice((*byte)(ptr), length)
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}
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