solved it:
//export Eb_TcpSecureStreamCreateListener
func Eb_TcpSecureStreamCreateListener(listenIp string, listenPort int)
unsafe.Pointer, retStatus {
pmap := &ThreadSafePeerMap{
....
....
}
server := Server{
....
....
}
server.listener = secConn.NewListener(server.listenAddress, server.ID)
//allocate memory on C heap. we send the server address in this pointer
//allocated memory is freed in Eb_TcpSecureStreamCloseListener()
serverMemAlloc := C.malloc(C.size_t(unsafe.Sizeof(uintptr(0))))
//create array to write the address in the array
a := (*[1]*Server)(serverMemAlloc)
//save the address in index 0 of the array
a[0] = &(*(*Server)(unsafe.Pointer(&server)))
return serverMemAlloc, C.Success
}
and the unsafe.Pointer receiver:
//export Eb_TcpSecureStreamCloseListener
func Eb_TcpSecureStreamCloseListener(listenerHandle unsafe.Pointer)
(retStatus int) {
if listenerHandle == nil {
return C.BadInput
}
server := *(*Server)((*[1]*Server)(listenerHandle)[0])
err := server.listener.Close()
//freeing listenerHandle regardless of Close() returned status
C.free(listenerHandle)
if err != nil {
return C.Error
}
return C.Success
}
thanks,
On Tuesday, December 18, 2018 at 5:14:45 PM UTC+2, Ian Lance Taylor wrote:
>
> On Tue, Dec 18, 2018 at 6:27 AM <eran....@gmail.com <javascript:>> wrote:
> >
> > I have to projects. One is cgo and one is C application.
> > The cgo has a function which needs to return pointer to struct.
> > The C app receives this pointer and then calls other function in cgo
> with this pointer.
> > I build the cgo as shared lib:
> >
> > go build -o ebsdk.so -buildmode=c-shared
> >
> > The cgo function is this:
> >
> > //export Eb_TcpSecureStreamCreateListener
> > func Eb_TcpSecureStreamCreateListener(listenIp string, listenPort int)
> unsafe.Pointer {
> >
> > pmap := &ThreadSafePeerMap{
> > peerMap: make(map[string]*Peer, 0),
> > Mutex: sync.RWMutex{},
> > }
> >
> > server := &Server{
> > ID: cert.Subject.CommonName,
> > listenAddress: listenIp + ":" + strconv.Itoa(listenPort),
> > libSecConn: secConn,
> > PeerMap: pmap,
> > InboundChannel: make(chan *TcpMessage, channelSize),
> > OutgoingChannel: make(chan *TcpMessage, channelSize),
> > ClosedConnections: make(chan *TcpMessage, channelSize),
> > shutdown: false,
> > }
> >
> > server.listener = secConn.NewListener(server.listenAddress, server.ID)
> >
> > return unsafe.Pointer(server)
> > }
> >
> > C code calls this cgo function with the returned unsafe.Pointer:
> >
> >
> > func Eb_TcpSecureStreamCloseListener(listenerHandle unsafe.Pointer)
> (retStatus int) {
> >
> > if listenerHandle == nil {
> > return C.BadInput
> > }
> >
> > server := *(*Server)(listenerHandle)
> >
> > err := server.listener.Close()
> > if err != nil {
> > return C.Error
> > }
> >
> > return C.Success
> > }
> >
> >
> > My problem is that Eb_TcpSecureStreamCreateListener() return statement
> cause panic: "runtime error: cgo result has Go pointer"
>
> See https://golang.org/cmd/cgo/#hdr-Passing_pointers . "A Go function
> called by C code may not return a Go pointer."
>
> I'm not sure what to suggest because I'm not sure what you are trying
> to do. One approach that works for some programs is to store the
> pointer in a Go map that uses integer keys, and return the map key.
> Since it looks like the struct can only be used from Go, the Go code
> can use the map key to look up the struct. Of course you then need to
> know when you can remove the struct from the map so that the garbage
> collector can release it.
>
> Ian
>
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