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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Capacity 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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// ConvertToSlice convert to []byte
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func ptr2Slice(s unsafe.Pointer, size int) []byte {
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var x reflect.SliceHeader
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x.Len = size
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x.Cap = size
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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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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) {
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sdi.Capacity = uint32(len(data))
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} else {
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sdi.Capacity = uint32(len(shmData))
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}
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tmpData := ptr2Slice(unsafe.Pointer(&sdi.Cache), int(sdi.Capacity))
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copy(tmpData, data)
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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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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.Capacity))
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return tmpData, nil
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}
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