documentation ambiguous about callbacks returning String

[strtok]

If calling a java callback that returns String, the return type is translated to char* on the native side. The documentation is unclear, though, about the lifetime of the string. Is the memory owned by java or should it be freed by C?

[strtok]

It looks like the char* is freed by JNA and is tied to the lifetime of the source String?

[twall]

JNA does what it can to make things easier for you, but fundamentally you
need to be aware of when you're passing memory buffers off to native
code. Once you do so, it's your responsibility to ensure that said
buffer will stick around as long as the native code needs it. JNA can't
predict that for you, but it at least gives you the option of keeping a
reference to the String as proxy for maintaining a reference to the
automatically generated native buffer. JNA in general will try to reclaim
any memory that it allocations, usually by GC when there are no longer any
extant referenes to the allocated memory.

A native API that receives a buffer without explicit information w/r/t its
lifecycle is a code smell. Consider passing a buffer and asking for it to
be populated instead.

Other, less desirable solutions are to document what's expected to be done
with the buffer, or using a global/static buffer.

On Thu, Jun 16, 2016 at 8:42 PM, Erik Bremen [email protected]
wrote:

It looks like the char* is freed by JNA and is tied to the lifetime of the
source String?

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[strtok]

Thanks. That clarifies what we found in the source. The intention for opening the bug was that the docs could use a note that in every case where JNA might return a pointer to native code (String -> char*, Memory, etc) that JNA maintains responsibility for freeing it and that the memory is directly associated with the lifetime of the object in java being mapped.