forking Java process with panama-foreign

Main.java

import java.lang.invoke.MethodType;

import jdk.incubator.foreign.CLinker;
import jdk.incubator.foreign.FunctionDescriptor;
import jdk.incubator.foreign.LibraryLookup;
import jdk.incubator.foreign.MemoryAddress;

// run with `java --add-modules jdk.incubator.foreign -Dforeign.restricted=permit Main.java`
//
// TODO
// - Sometimes the child process hangs
public class Main {
    public static void main(String...args) throws Throwable {
        var lookup = LibraryLookup.ofDefault();
        var linker = CLinker.getInstance();

        var fork = linker.downcallHandle(
                lookup.lookup("fork").get(),
                MethodType.methodType(int.class),
                FunctionDescriptor.of(CLinker.C_INT));

        var waitpid = linker.downcallHandle(
                lookup.lookup("waitpid").get(),
                MethodType.methodType(int.class, int.class, MemoryAddress.class, int.class),
                FunctionDescriptor.of(CLinker.C_INT, CLinker.C_INT, CLinker.C_POINTER, CLinker.C_INT));

        var _exit = linker.downcallHandle(
                lookup.lookup("_exit").get(),
                MethodType.methodType(void.class, int.class),
                FunctionDescriptor.ofVoid(CLinker.C_INT));


        System.out.println("forking..");
        var child = (int) fork.invokeExact();
        System.out.println("forked.");

        if (child == 0) {
            System.out.println("I am child");
            _exit.invokeExact(0);

        } else if (child < 0) {
            throw new Exception("failed to fork");

        } else {
            System.out.println("I am parent");
            @SuppressWarnings("unused")
            var r = (int) waitpid.invokeExact(child, MemoryAddress.NULL, 0);
        }
    }
}

Sometimes the child process hangs

ok

$ java --add-modules jdk.incubator.foreign -Dforeign.restricted=permit Main.java
WARNING: Using incubator modules: jdk.incubator.foreign
warning: using incubating module(s): jdk.incubator.foreign
1 warning
forking..
forked.
forked.
I am child
I am parent
$

ng

$ java --add-modules jdk.incubator.foreign -Dforeign.restricted=permit Main.java
WARNING: Using incubator modules: jdk.incubator.foreign
warning: using incubating module(s): jdk.incubator.foreign
1 warning
forking..
forked.
I am parent

$ pgrep java
7772
7802
$ ls /tmp/hsperfdata_*
7772
$

Maybe java isn't designed to fork?