[foreign-jextract] [Rev 01] RFR: 8241925: jextract should generate simple allocation, access API for C primitive types

[Maurizio Cimadamore]

On Wed, 1 Apr 2020 02:55:42 GMT, Athijegannathan Sundararajan <sundar at openjdk.org> wrote:

>> added static method helper classes to handle allocation, access ot C primitive types and C strings.
>
> Athijegannathan Sundararajan has updated the pull request incrementally with one additional commit since the last
> revision:
>   * added static modifier to Cstring.toString method. Added tests for Cstring methods
>   * added length accepting allocateArray overloadeds and using the same in samples.
>   * using bulk copy for array copy
>   * fixed samples to use Cstring method instead of methods from Foreign.

Looks very good - some minor comments

doc/panama_jextract.md line 298:

> 297:       try (AllocationScope scope = AllocationScope.unboundedNativeScope()) {
> 298:             var a = Cdouble.allocateArray(m*n, scope);
> 299:             var x = Cdouble.allocateArray(n, scope);

there are some indentation issues in this example

doc/panama_jextract.md line 303:

> 302:             /* The elements of the first column */
> 303:             Cdouble.set(a, 0, 1.0);
> 304:             Cdouble.set(a, 1, 2.0);

Not sure whether `C_double` would be better than `Cdouble`, but we can tweak later

doc/panama_jextract.md line 330:

> 329:             Cdouble.set(y, 2, 0.0);
> 330:             Cdouble.set(y, 3, 0.0);
> 331:             cblas_dgemv(Layout, transa, m, n, alpha, a, lda, x, incx, beta, y, incy);

We also need an helper that takes a MemorySegment, interprets it as a native double array and turns it into a Java
double array. e.g. double[] toJavaArray(MemorySegment)
Not needed here, but could be handy in other cases

doc/panama_jextract.md line 166:

> 165:             // convert char* ptr from readline as Java String & print it
> 166:             System.out.println("Hello, " + Cstring.toString(p));
> 167:         }

I suggest calling this `toJavaString` to avoid confusion

-------------

PR: https://git.openjdk.java.net/panama-foreign/pull/78