RFR: 8264774: Implementation of Foreign Function and Memory API (Incubator)

[Chris Hegarty]

On Tue, 27 Apr 2021 18:40:24 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> This PR contains the API and implementation changes for JEP-412 [1]. A more detailed description of such changes, to avoid repetitions during the review process, is included as a separate comment.
>> 
>> [1] - https://openjdk.java.net/jeps/412
>
> src/java.base/share/classes/sun/nio/ch/IOUtil.java line 466:
> 
>> 464:     }
>> 465: 
>> 466:     private static final JavaNioAccess NIO_ACCESS = SharedSecrets.getJavaNioAccess();
> 
> It might be cleaner to move to acquire/release methods to their own supporting class as it's not really IOUtil.

I went back and forth on this a number of times already. I think where we landed is a reasonable place, given the current shape of the code.

Scope is a private property of Buffer, and as such should be consulted anywhere where a buffer's address is being accessed. In fact, a prior prototype would not allow access to the underlying address value without the caller passing a valid handle for the buffer view's scope. It's hard to find the sweet-spot here between code reuse and safety, but the high-order bit is that the code accessing the address is auditable and testable to avoid accessing memory unsafely. Maybe there is a better alternative implementation code structure (at the cost of some duplication), but it is not obvious to me what that is (and I have given it some thought). Suggestions welcome.

Note, there is a little more follow-on work to be done in this area, if we are to expand support to other non-TCP channel implementations. Maybe investigation into possible code refactorings could be done as part of that?

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PR: https://git.openjdk.java.net/jdk/pull/3699