[foreign] RFR 8213343: Update the public access mode API

[Jorn Vernee]

And I suppose it's useful if I include the actual AccessMode class in 
the webrev as well (oops)

Webrev: 
http://cr.openjdk.java.net/~jvernee/panama/webrevs/accessmode/webrev.01/

Cheers,
Jorn

Jorn Vernee schreef op 2018-11-21 00:14:
> Hi,
> 
> While reading through the Pointer class, I noticed there is a method
> `isAccessibleFor(int)` which is used to check if the pointer is
> accessible for a certain access mode.
> 
> The problem is that the `int` value that's expected as an argument is
> defined as the constants MODE_R, MODE_W and MODE_RW in
> BoundedMemoryRegion [1]. This is in an internal package, so there will
> be no way for the user to use those constants.
> 
> The other problem is that having an `int` as the argument type gives
> no hint to what values can be used there. I would like to advocate for
> switching to an enum there, since then it's a simple case of typing in
> the enum name, hitting the auto-complete key and getting a list of
> available argument values.
> 
> The third problem is that there seems to be no public API point for
> setting the access mode of a Pointer. I can imagine that somebody
> might want to give out a read-only pointer to a client (and maybe even
> a write-only pointer).
> 
> I have a patch that attempts to solve all 3 problems;
> 
> 1 & 2: I have created an AccessMode enum in j.f.memory that is used in
> place of the `int`s.
> 3: I have added 2 methods to Pointer, asReadOnly and asWriteOnly, to
> create a new pointer from the given one with either of the 2 access
> modes.
> 
> As an additional cleanup I've also removed the mode field from
> BoundedPointer, since it was unused, and made the other fields private
> instead of public. In order to do the latter, I added
> putLongBits/getLongBits methods to BoundedPointer, which replaces
> direct access to the pointer's region put/get methods. I also added a
> package declaration to ArrayTest since my IDE (thanks Maurizio ;P) was
> complaining about a duplicate class, since there was a test class with
> the same name in the jextract test directory.
> 
> Related bug: https://bugs.openjdk.java.net/browse/JDK-8213343
> Webrev: 
> http://cr.openjdk.java.net/~jvernee/panama/webrevs/accessmode/webrev.00/
> 
> Please let me know what you think about this.
> 
> Thanks,
> Jorn
> 
> [1] :
> http://hg.openjdk.java.net/panama/dev/file/cfee9bc4ebe4/src/java.base/share/classes/jdk/internal/foreign/memory/BoundedMemoryRegion.java#l33