package shmqueue
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import (
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"reflect"
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"unsafe"
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)
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// []byte struct
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type ShmDataInfo struct {
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Len uint32
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Cache []byte
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}
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// shmData2Info convert []byte to *ShmDataInfo
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func shmData2Info(b []byte) *ShmDataInfo {
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return (*ShmDataInfo)(unsafe.Pointer(
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(*reflect.SliceHeader)(unsafe.Pointer(&b)).Data,
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))
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}
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const SHMSLICEOFFSET int = 32
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// ConvertToSlice convert to []byte
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func ptr2Slice(s unsafe.Pointer, size,cap int) []byte {
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var x reflect.SliceHeader
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x.Len = size
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x.Cap = cap
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x.Data = uintptr(s)
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return *(*[]byte)(unsafe.Pointer(&x))
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}
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//WriteShmData data待写入的数据; shmId:共享内存id,只attach,不create
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// 把data写入shmId对应的shm中, 流程: attach->写入数据->detach
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// 适合shm是空的,解码使用
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func WriteShmData(data []byte, shmId int) error {
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shmData, err := Attach(shmId)
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if err != nil {
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return err
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}
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sdi := shmData2Info(shmData)
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if len(data) <= len(shmData)-SHMSLICEOFFSET {
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sdi.Len = uint32(len(data))
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} else {
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sdi.Len = uint32(len(shmData)-SHMSLICEOFFSET)
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}
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tmpData := ptr2Slice(unsafe.Pointer(&sdi.Cache), int(sdi.Len), len(shmData)-SHMSLICEOFFSET)
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copy(tmpData, data)
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err = Detach(shmData)
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if err != nil {
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return err
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}
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return nil
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}
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//ReadShmData attach到shmId对应的共享内存,并读出数据[]byte
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// 使用之后需要detach
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func ReadShmData(shmId int) ([]byte, error) {
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shmData, err := Attach(shmId)
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if err != nil {
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return nil, err
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}
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sdi := shmData2Info(shmData)
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tmpData := ptr2Slice(unsafe.Pointer(&sdi.Cache), int(sdi.Len), len(shmData)-SHMSLICEOFFSET)
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return tmpData, nil
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}
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//DeepCopyDataToShm 深拷贝,把内存的数据拷贝attach之后共享内存中
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// 输入: shmData是attach返回的[]byte, memdData是内存中的数据
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// 写入数据到共享内存使用:attach->DeepCopyDataToShm->detach
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// 适合解码使用
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func DeepCopyDataToShm(memData,shmData []byte) {
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sdi := shmData2Info(shmData)
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if len(memData) <= len(shmData)-SHMSLICEOFFSET {
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sdi.Len = uint32(len(memData))
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} else {
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sdi.Len = uint32(len(shmData)-SHMSLICEOFFSET)
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}
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tmpData := ptr2Slice(unsafe.Pointer(&sdi.Cache), int(sdi.Len), len(shmData)-SHMSLICEOFFSET)
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copy(tmpData, memData)
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}
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//ReadShmData 把attach后的shmData转成内存data
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// 输入:attach到共享内存得到的shmData
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// 输出:转换后的data
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// 从共享内存中读取数据使用:attach->ConvertShmToData->只读,业务处理结束后->detach
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func ConvertShmToData(shmData []byte) []byte {
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sdi := shmData2Info(shmData)
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tmpData := ptr2Slice(unsafe.Pointer(&sdi.Cache), int(sdi.Len), len(shmData)-SHMSLICEOFFSET)
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return tmpData
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}
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//UpdateDataToShm (类似浅拷贝)更新数据到共享内存
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// 输入: ConvertShmToData得到的数据data,经过业务处理后,该数据有变化,需要update到shm里
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// 更新数据到共享内存使用: attach->ConvertShmToData->修改data数据,业务处理结束后->UpdateDataToShm->detach
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func UpdateDataToShm(data, shmData []byte) {
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sdi := shmData2Info(shmData)
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sdi.Len = uint32(len(data))
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}
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