On Sat, Aug 19, 2017, 8:38 AM Ian Lance Taylor <i...@golang.org> wrote:
> On Fri, Aug 18, 2017 at 8:59 AM, Bhaskar Singhal
> <bhaskar.sing...@gmail.com> wrote:
> >
> > C function just copies the parameters passed. All of the params have
> escaped
> > to heap as seen in output generated by using -gcflags "-m -m" during
> build.
> >
> > I am trying to figure out if there is a possibility that gc frees any of
> > these parameters before the C function call returns.
>
> Go's garbage collector never frees memory allocated by C.CString, just
> as it never frees memory allocated by C.malloc.
>
> Ian
>
>
> > On Fri, Aug 18, 2017 at 7:57 PM, Ian Lance Taylor <i...@golang.org>
> wrote:
> >>
> >> On Fri, Aug 18, 2017 at 12:53 AM, Bhaskar Singhal
> >> <bhaskar.sing...@gmail.com> wrote:
> >> > I am running into a seg fault. The code keeps crashing either due to
> >> > unexpected signal or double free.
> >> >
> >> > Any pointers on what I am doing wrong here:
> >> >
> >> > Code Snippet:
> >> > // Put puts the given key / value to the kvstore
> >> > func (kvs *kvstore) Put(key []byte, value []byte) error {
> >> > /* Encode key to avoid null characters in byte[] */
> >> > strk := base64.StdEncoding.EncodeToString([]byte(key))
> >> > csk := C.CString(strk)
> >> > defer C.free(unsafe.Pointer(csk))
> >> >
> >> > /* Encode value to avoid null characters in byte[] */
> >> > strv := base64.StdEncoding.EncodeToString([]byte(value))
> >> > csv := C.CString(strv)
> >> > defer C.free(unsafe.Pointer(csv))
> >> >
> >> > if kvs.kvtree == nil {
> >> > return fmt.Errorf("put failed because kvtree is nil")
> >> > }
> >> > size := C.int32_t(len(strv))
> >> >
> >> > ret := C.put(kvs.kvtree, csk, csv, &size)
> >> > if ret != C.int8_t(1) {
> >> > return fmt.Errorf("kvtree put failed %g", ret)
> >> > }
> >> > return nil
> >> > }
> >> >
> >> > C Function Put:
> >> > int8_t put(KVTree* kv,
> >> > const char* key,
> >> > const char* value,
> >> > const int32_t* valuebytes);
> >>
> >>
> >> It really depends on how the C function behaves. My guess is that it
> >> does not expect the values to be freed.
> >>
> >> Ian
> >
> >
>
I have cgo code that looks like this in a few of my own libs and I just
started seeing crashes like this as of Go 1.8. Could it be related to the
need for using runtime.KeepAlive? I have been adding that to my functions
that look like this
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