1

使用 JDK 16 中的 FFI 预览，我有这样的内存布局：

class FfiTest {
    static GroupLayout layout = MemoryLayout.ofStruct(
        C_INT.withName("someInt"),
        MemoryLayout.ofPaddingBits(32), // So the following pointer is aligned at 64 bits
        C_POINTER.withName("somePtr")
    );
}

然后，我在本机代码的回调中收到指向此类结构的指针：

public static void someCallback(MemoryAddress address) {
    try (MemorySegment seg = address.asSegmentRestricted(FfiTest.layout.byteSize())) {                

        // Works: fetching int from native structure, correct value is returned
        VarHandle intHandle = FfiTest.layout.varHandle(int.class, MemoryLayout.PathElement.groupElement("someInt"));
        int intResult = (int) vh.get(seg);

        // Does not work: get the pointer as a MemoryAddress, fatal JVM crash with Hotspot log
        VarHandle badPtrHandle = FfiTest.layout.varHandle(MemoryAddress.class, MemoryLayout.PathElement.groupElement("somePtr"));

        // Works: get the pointer as a long, correct value is returned
        VarHandle goodPtrHandle = FfiTest.layout.varHandle(long.class, MemoryLayout.PathElement.groupElement("somePtr"));
        long longResult = (long) goodPtrHandle.get(seg);
    }
}

在 JDK 代码中引发异常jdk.internal.foreign.Utils：

    public static void checkPrimitiveCarrierCompat(Class<?> carrier, MemoryLayout layout) {
        checkLayoutType(layout, ValueLayout.class);
        if (!isValidPrimitiveCarrier(carrier))
            throw new IllegalArgumentException("Unsupported carrier: " + carrier); // Throws this exception, carrier has the value MemoryAddress
        if (Wrapper.forPrimitiveType(carrier).bitWidth() != layout.bitSize())
            throw new IllegalArgumentException("Carrier size mismatch: " + carrier + " != " + layout);
    }

根据巴拿马文档， a 的 Java 载体C_POINTER应该是MemoryAddress，但这在这里不起作用。

那么使用 long 来访问此类指针是否正确？或者是其他东西？

4

1 回答 1

2

正如约翰内斯在评论中指出的那样，MemoryHandles::asAddressVarHandle可用于调整long您必须接受的句柄并返回 a MemoryAddress：

VarHandle goodPtrHandle = FfiTest.layout.varHandle(long.class, MemoryLayout.PathElement.groupElement("somePtr"));
long longResult = (long) goodPtrHandle.get(seg);
VarHandle addrHandle = MemoryHandles.asAddressVarHandle(goodPtrHandle);
MemoryAddress addrResult = (MemoryAddress) addrHandle.get(seg);
于 2021-03-19T11:53:15.410 回答