[foreign-abi] RFR: 8254682: Close MemorySegments passed to upcalls after the upcall is done

[Maurizio Cimadamore]

On Tue, 13 Oct 2020 14:58:29 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

> Hi,
> 
> Currently, we don't close MemorySegments that we pass to upcalls. This makes it easier to leak a MemorySegment from an
> upcall, but it also incurs an additional copy on Windows and Aarch64, and forces users to close these segments manually
> instead. (This is mostly so for historical reasons, when it was not as easy to avoid this copy due to the code
> structure/design at that time).  We can instead registers these segments with a NativeScope that is closed after the
> upcall completes, to make sure these segments do not leak inadvertently, and we don't need the additional copy on some
> platforms.   In this PR I've also fixed 2 minor Javadoc issues in Binding.java that I missed last time around.
> This patch will also break jexract tests, but I have a patch ready to fix (was pretty trivial).
> (https://github.com/openjdk/panama-foreign/pull/380)
> Thanks,
> Jorn

Looks good

src/jdk.incubator.foreign/share/classes/jdk/internal/foreign/AbstractNativeScope.java line 140:

> 138:
> 139:     // only for registering
> 140:     private static class EmptyScope extends AbstractNativeScope {

could this be your Throwing Allocator?

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Marked as reviewed by mcimadamore (Committer).

PR: https://git.openjdk.java.net/panama-foreign/pull/379