Thanks! The only information I could find about this on the gobind
documentation is (https://godoc.org/golang.org/x/mobile/cmd/gobind)
- Byte slice types. Note that byte slices are passed by reference,
and support mutation.
However, this version of the code still shows the problem:
> String s = "This is a test string";
> byte[] b = s.getBytes();
> MyStruct struct = new MyStruct(b);
> tv.append("\nFirst time: "+ new String(struct.getE(), "UTF-8"));
> tv.append("\nOriginal: "+ new String(b, "UTF-8"));
>
>
which is confusing as here b shold not be garbage collected, so even a pass
by reference should work. Can you point me somewhere I can read more about
this issue please?
Also, are the automatically generated setters (i.e. struct.setE() ) doing
the necessary cloning, or should I implement my own?
Thanks a lot again!
On Thursday, August 3, 2017 at 1:33:03 AM UTC-7, Elias Naur wrote:
>
> Yes, byte slices are special and are not reference counted like other
> objects. You need to copy it on the Go side.
>
> - elias
>
> Den tor. 3. aug. 2017 03.21 skrev Antonio Marcedone <a.mar...@gmail.com
> <javascript:>>:
>
>> My intuition above seems to contrast with
>> https://godoc.org/golang.org/x/mobile/cmd/gobind:
>>
>> Avoid reference cycles
>>> The language bindings maintain a reference to each object that has been
>>> proxied. When a proxy object becomes unreachable, its finalizer reports
>>> this fact to the object's native side, so that the reference can be
>>> removed, potentially allowing the object to be reclaimed by its native
>>> garbage collector. The mechanism is symmetric.
>>
>>
>>
>> On Wednesday, August 2, 2017 at 5:30:16 PM UTC-7, Antonio Marcedone wrote:
>>>
>>> I am not sure I understand what is going on here.
>>> For reference, the relevant code is:
>>>
>>> String s = "This is a test string";
>>>
>>> MyStruct struct = new MyStruct(s.getBytes("UTF-8"));
>>> //struct.setE(s.getBytes("UTF-8"));
>>> tv.append("\nFirst time: "+ new String(struct.getE(), "UTF-8"));
>>>
>>>
>>> with corresponding go part:
>>>
>>> package test
>>>
>>> type MyStruct struct{
>>> E []byte}
>>>
>>> func NewMyStruct(e []byte) *MyStruct{
>>> return &MyStruct{e}}
>>>
>>>
>>> so s.getBytes allocates a new byte[] (in Java). Then the MyStruct
>>> constructor is called, and it gets a reference to such byte[].
>>> Are you saying that since the Java garbage collector is not aware that a
>>> reference to that array is stored in some variable in the go code, then it
>>> just deletes it as soon as the constructor returns?
>>> And then the getE method just reads whatever happens to be in memory
>>> where the old array was without throwing any error despite the fact that
>>> the old byte[] has been garbage collected and might have been overwritten
>>> by arbitrary data?
>>>
>>> Thanks a lot for your response!
>>> Antonio
>>>
>>> On Wednesday, August 2, 2017 at 3:30:06 PM UTC-7, Elias Naur wrote:
>>>>
>>>> []byte arguments are passed by reference, not copied. You need to copy
>>>> any byte slices you retain after the function or method call.
>>>>
>>>> - elias
>>>>
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