Why asUnbounded()/isUnbounded() was removed in JDK21?

[Maurizio Cimadamore]

Hi,
the functionality is there - it has just been renamed to make it more 
general.

In 20, one could only create an address layout that was _unbounded_ e.g. 
that pointed to a region of memory of unbounded size.

In 21, AddressLayout is a new toplevel class. An address layout has a 
_target layout_ [1] which is used to describe the layout of the pointed 
region of memory.

This means that you can still get a behavior similar to `asUnbounded`, 
by doing:

```java
ADDRESS.withTargetLayout(MemoryLayout.sequenceLayout(JAVA_BYTE))
```

The above will create a sequence layout of unbound size (so, the size of 
that layout would be Long.MAX_VALUE), and use that layout as the target 
for the address layout. Which means that when this address is passed to 
MemorySegment::get(AddressLayout), or to the Linker, you will get back a 
MemorySegment whose size is Long.MAX_VALUE (as in 21).

But, if you know the layout of the pointed region of memory statically, 
you can also use a sharper target layout - e.g.

```java
ADDRESS.withTargetLayout(JAVA_INT)
```

The latter will create an address layout whose target layout is 
_exactly_ one int layout. This means that when you pass this address 
layout to MemorySegment::get(AddressLayout),or to the Linker, you will 
get back a MemorySegment whose size is precisely 4 bytes. This is 
especially useful for upcalls (as the qsort example in JEP 442 
demonstrates).

Hope this helps.

Maurizio

[1] - 
https://cr.openjdk.org/~pminborg/panama/21/v2/javadoc/api/java.base/java/lang/foreign/AddressLayout.html#withTargetLayout(java.lang.foreign.MemoryLayout)


On 03/05/2023 14:34, Cheng Jin wrote:
>
> Hi there,
>
> I am wondering why asUnbounded()/isUnbounded() (existing in JDK20) 
> related code was removed from 
> java.base/share/classes/java/lang/foreign/ValueLayout.java in JDK21.
>
> Is there any reason for deleting them all (or moving them somewhere 
> else which I ignored) for the unbounded segment (pointer)?
>
> Best Regards
>
> Cheng Jin
>
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