Java 17 更新（10）：访问外部函数的新 API，JNI 要凉了？

System.loadLibrary("libsimple");
SymbolLookup loaderLookup = SymbolLookup.loaderLookup();
MemoryAddress getCLangVersion = loaderLookup.lookup("GetCLangVersion").get();

int GetCLangVersion() {
  return __STDC_VERSION__;
}

MethodHandle getClangVersionHandle = CLinker.getInstance().downcallHandle(
    getCLangVersion,
    MethodType.methodType(int.class),
    FunctionDescriptor.of(C_INT)
);
System.out.println(getClangVersionHandle.invoke());

-Djava.library.path=./lib/bin

201112

MemoryAddress strlen = CLinker.systemLookup().lookup("strlen").get();
MethodHandle strlenHandle = CLinker.getInstance().downcallHandle(
    strlen,
    MethodType.methodType(int.class, MemoryAddress.class),
    FunctionDescriptor.of(C_INT, C_POINTER)
);

var string = CLinker.toCString("Hello World!!", ResourceScope.newImplicitScope());
System.out.println(strlenHandle.invoke(string.address()));

13

typedef struct Person {
  long long id;
  char name[10];
  int age;
} Person;

void DumpPerson(Person *person) {
  printf("Person%%%lld(id=%lld, name=%s, age=%d)\n",
         sizeof(Person),
         person->id,
         person->name,
         person->age);

  char *p = person;
  for (int i = 0; i < sizeof(Person); ++i) {
    printf("%d, ", *p++);
  }
  printf("\n");
}

MemoryLayout personLayout = MemoryLayout.structLayout(
    C_LONG_LONG.withName("id"),
    MemoryLayout.sequenceLayout(10, C_CHAR).withName("name"),
    MemoryLayout.paddingLayout(16),
    C_INT.withName("age"));

MemorySegment person = MemorySegment.allocateNative(personLayout, newImplicitScope());

VarHandle idHandle = personLayout.varHandle(long.class, MemoryLayout.PathElement.groupElement("id"));
idHandle.set(person, 1000000);

var ageHandle = personLayout.varHandle(int.class, MemoryLayout.PathElement.groupElement("age"));
ageHandle.set(person, 30);

 VarHandle nameHandle = personLayout.varHandle(
     byte.class,
     MemoryLayout.PathElement.groupElement("name"),
     MemoryLayout.PathElement.sequenceElement()
 );

byte[] bytes = "bennyhuo".getBytes();
for (int i = 0; i < bytes.length; i++) {
    nameHandle.set(person, i, bytes[i]);
}
nameHandle.set(person, bytes.length, (byte) 0);

person.asSlice(personLayout.byteOffset(MemoryLayout.PathElement.groupElement("name")))
             .copyFrom(CLinker.toCString("bennyhuo", newImplicitScope()));

MemoryAddress dumpPerson = loaderLookup.lookup("DumpPerson").get();
MethodHandle dumpPersonHandle = CLinker.getInstance().downcallHandle(
    dumpPerson,
    MethodType.methodType(void.class, MemoryAddress.class),
    FunctionDescriptor.ofVoid(C_POINTER)
);

dumpPersonHandle.invoke(person.address());

Person%24(id=1000000, name=bennyhuo, age=30)
64, 66, 15, 0, 0, 0, 0, 0, 98, 101, 110, 110, 121, 104, 117, 111, 0, 0, 0, 0, 30, 0, 0, 0, 

for (byte b : person.toByteArray()) {
    System.out.print(b + ", ");
}
System.out.println();

typedef void (*OnEach)(int element);

void ForEach(int array[], int length, OnEach on_each) {
  for (int i = 0; i < length; ++i) {
    on_each(array[i]);
  }
}

public static void onEach(int element) {
    System.out.println("onEach: " + element);
}

MethodHandle onEachHandle = MethodHandles.lookup().findStatic(
    ForeignApis.class, "onEach",
    MethodType.methodType(void.class, int.class)
);

MemoryAddress onEachHandleAddress = CLinker.getInstance().upcallStub(
    onEachHandle, FunctionDescriptor.ofVoid(C_INT), newImplicitScope()
);

int[] originalArray = new int[]{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
MemorySegment array = MemorySegment.allocateNative(4 * 10, newImplicitScope());
array.copyFrom(MemorySegment.ofArray(originalArray));

MemoryAddress forEach = loaderLookup.lookup("ForEach").get();
MethodHandle forEachHandle = CLinker.getInstance().downcallHandle(
    forEach,
    MethodType.methodType(void.class, MemoryAddress.class, int.class, MemoryAddress.class),
    FunctionDescriptor.ofVoid(C_POINTER, C_INT, C_POINTER)
);
forEachHandle.invoke(array.address(), originalArray.length, onEachHandleAddress);

onEach: 1
onEach: 2
onEach: 3
onEach: 4
onEach: 5
onEach: 6
onEach: 7
onEach: 8
onEach: 9
onEach: 10