src/java.base/share/classes/java/lang/foreign/AddressLayout.java

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package java.lang.foreign;

import jdk.internal.foreign.layout.ValueLayouts;
import jdk.internal.javac.Restricted;
import jdk.internal.reflect.CallerSensitive;

import java.lang.foreign.Linker.Option;
import java.lang.invoke.MethodHandle;
import java.nio.ByteOrder;
import java.util.Optional;

/**
 * A value layout used to model the address of some region of memory. The carrier
 * associated with an address layout is {@code MemorySegment.class}. The size and
 * alignment of an address layout are platform-dependent (e.g. on a 64-bit platform,
 * the size and alignment of an address layout are set to 8 bytes).
 * <p>
 * An address layout may optionally feature a {@linkplain #targetLayout() target layout}.
 * An address layout with target layout {@code T} can be used to model the address of a
 * region of memory whose layout is {@code T}. For instance, an address layout with
 * target layout {@link ValueLayout#JAVA_INT} can be used to model the address of a
 * region of memory that is 4 bytes long. Specifying a target layout can be useful in
 * the following situations:
 * <ul>
 *     <li>When accessing a memory segment that has been obtained by reading an address from
 *     another memory segment, e.g. using {@link MemorySegment#getAtIndex(AddressLayout, long)};</li>
 *     <li>When creating a downcall method handle, using {@link Linker#downcallHandle(FunctionDescriptor, Option...)};
 *     <li>When creating an upcall stub, using {@link Linker#upcallStub(MethodHandle, FunctionDescriptor, Arena, Option...)}.
 * </ul>
 *
 * @implSpec
 * Implementations of this interface are immutable, thread-safe and
 * <a href="{@docRoot}/java.base/java/lang/doc-files/ValueBased.html">value-based</a>.
 *
 * @see #ADDRESS
 * @see #ADDRESS_UNALIGNED
 * @since 22
 */
public sealed interface AddressLayout extends ValueLayout permits ValueLayouts.OfAddressImpl {

    /**
     * {@inheritDoc}
     */
    @Override
    AddressLayout withName(String name);

    /**
     * {@inheritDoc}
     */
    @Override
    AddressLayout withoutName();

    /**
     * {@inheritDoc}
     */
    @Override
    AddressLayout withByteAlignment(long byteAlignment);

    /**
     * {@inheritDoc}
     */
    @Override
    AddressLayout withOrder(ByteOrder order);

    /**
     * Returns an address layout with the same carrier, alignment constraint, name and
     * order as this address layout, but associated with the specified target layout.
     * The returned address layout allows raw addresses to be accessed as
     * {@linkplain MemorySegment memory segments} whose size is set to the size of the
     * specified layout. Moreover, if the accessed raw address is not compatible with
     * the alignment constraint in the provided layout, {@linkplain IllegalArgumentException}
     * will be thrown.
     * @apiNote
     * This method can also be used to create an address layout which, when used, creates
     * native memory segments with maximal size (e.g. {@linkplain Long#MAX_VALUE}). This
     * can be done by using a target sequence layout with unspecified size, as follows:
     * {@snippet lang = java:
     * AddressLayout addressLayout   = ...
     * AddressLayout unboundedLayout = addressLayout.withTargetLayout(
     *         MemoryLayout.sequenceLayout(Long.MAX_VALUE, ValueLayout.JAVA_BYTE));
     *}
     *
     * @param layout the target layout
     * @return an address layout with same characteristics as this layout, but with the
     *          provided target layout
     * @throws IllegalCallerException if the caller is in a module that does not have
     *         native access enabled
     * @see #targetLayout()
     */
    @CallerSensitive
    @Restricted
    AddressLayout withTargetLayout(MemoryLayout layout);

    /**
     * Returns an address layout with the same carrier, alignment constraint, name and
     * order as this address layout, but with no target layout.
     *
     * @apiNote This can be useful to compare two address layouts that have different
     *          target layouts, but are otherwise equal.
     *
     * @return an address layout with same characteristics as this layout, but with no
     *         target layout
     * @see #targetLayout()
     */
    AddressLayout withoutTargetLayout();

    /**
     * {@return the target layout associated with this address layout (if any)}
     */
    Optional<MemoryLayout> targetLayout();

}