Kotlin FFI samples

Contains samples of FFI usage from Kotlin:

Note: require Kotlin M10 or later

1. pidtest - direct port of JNR GetPid sample (https://github.com/jnr/jnr-ffi-examples/tree/master/getpid/src/main/java/getpid)

2. armatest - example of using sample wrapper around Armadillo (http://arma.sourceforge.net/) lib via JNR, reproducing tutorial sample from the lib. (wrapper could be taken from https://github.com/ligee/armadillo-4ffi, compiled library should be placed into the folder where jnr-ffi loader may find it, e.g. in the project root)

3. ffi-bench - benchmarking various FFI approaches:

   • JNI
   • JNR
   • BridJ - works with some problems, namely value extraction from struct doesn't work

ffi-bench results:

JNR results (10000 repeats, calibrated to 0us)

int->int: 2732us
string->int: 48087us
int->string: 2288us
int->struct1: 19321us
struct1->int: 7321us
callback->int: 11167us

JNI results (10000 repeats, calibrated to 0us)

int->int: 2009us
string->int: 6210us
int->string: 2756us
int->struct1: 17029us
struct1->int: 8899us
callback->int: 7004us

BridJ results (10000 repeats, calibrated to 0us)

int->int: 2158us
string->int: 50564us
int->string: 2098us
int->struct1: 11100us
struct1->int: 5650us
callback->int: 10994us