e been violating cgo rules by passing Go pointer to an integer to the C
code for storage.
C.nlopt_set_max_objective(n.gopt,
(C.nlopt_func)(unsafe.Pointer(C.callback_adaptor)), unsafe.Pointer(&nID))
Now I do it like this instead:
C.nlopt_set_max_objective(n.gopt,
(C.nlopt_func)(unsafe.Pointer(C.callback_adaptor)),
unsafe.Pointer(uintptr(nID)))
And the problem is gone.
Thanks for your help,
Iakov
On Thursday, November 10, 2016 at 3:32:02 PM UTC+1, iakov....@gmail.com
wrote:
>
> Hi,
> I don't have a minimal example yet, but this looks very suspicious. It
> seems that sometimes defer called before the function finishes, if cgo code
> with callbacks is called in it.
>
> Here's the code:
>
> func (n *NLOPT) Run(iterations int) {
> log.Debug("entering Run method")
> ...
> nID := registerObject(n)
> defer unregisterObject(nID)
> ...
> // this will call some go function
> n.optRes = C.nlopt_optimize(n.gopt,
> (*C.double)(unsafe.Pointer(&x[0])), &maxf)
> ....
> log.Debug("leaving Run method")
> }
>
>
> Here's what I see in my logs:
>
> entering Run method
> register: 1 (0xc82000a900)
> ... other messages, no "leaving Run method" ...
> unregister: 1 (0xc82000a900)
> panic: interface conversion: interface {} is nil, not *optimize.NLOPT
> (this panic happens because something was prematurely unregistered)
>
> So defer is executed before the method exits.
>
> I tried this in go v1.5 and v1.7, linux64. Sometimes it happens not
> immediately, but after some time.
>
> Are there any special defer rules regarding cgo & callbacks which I do not
> know?
>
> Thanks a lot for your suggestions,
> Iakov
>
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