JDK-8249753: Add restricted factory to access everything segment

[mcimadamore]

This patch adds another restricted factory, namely MemorySegment::ofRestrictedNative(). The new factory takes no arguments and return a segment that has the following characteristics:

• its base address is MemoryAddress::NULL
• its size is Long.MAX_VALUE
• it is non-closeable
• it is not confined

Note that this is not exactly the everything segment, since, at least in principle, addressable space goes up to 2 ^ 64 - 1 while Long::MAX_VALUE is "only" 2^63 -1. In other words, there is a possibility for some addresses to show up as negative long values, which will then be rejeced during dereference.

That said, for all intent and purposes, the segment returned by the new factory is a close enough approximation to the everything segment; we'd prefer to start with that and expand later (with some concrete use cases) rather than adding a new kind of memory segment which might not be needed.

---

Progress

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Issue

• JDK-8249753: Add restricted factory to access everything segment

Reviewers

• Jorn Vernee (jvernee - Committer)

Download

$ git fetch https://git.openjdk.java.net/panama-foreign pull/249/head:pull/249
$ git checkout pull/249

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@mcimadamore This change now passes all automated pre-integration checks, type /integrate in a new comment to proceed. After integration, the commit message will be:

8249753: Add restricted factory to access everything segment

Reviewed-by: jvernee

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[mcimadamore]

/integrate

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Pushed as commit 0c76b50.