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package jdk.internal.foreign;

import jdk.incubator.foreign.MemorySegment;
import jdk.internal.access.foreign.UnmapperProxy;
import jdk.internal.misc.ScopedMemoryAccess;
import sun.nio.ch.FileChannelImpl;

import java.io.FileDescriptor;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import java.nio.file.OpenOption;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.util.Objects;
import java.util.Optional;

Implementation for a mapped memory segments. A mapped memory segment is a native memory segment, which additionally features an UnmapperProxy object. This object provides detailed information about the memory mapped segment, such as the file descriptor associated with the mapping. This information is crucial in order to correctly reconstruct a byte buffer object from the segment (see makeByteBuffer()). /**
 * Implementation for a mapped memory segments. A mapped memory segment is a native memory segment, which
 * additionally features an {@link UnmapperProxy} object. This object provides detailed information about the
 * memory mapped segment, such as the file descriptor associated with the mapping. This information is crucial
 * in order to correctly reconstruct a byte buffer object from the segment (see {@link #makeByteBuffer()}).
 */
public class MappedMemorySegmentImpl extends NativeMemorySegmentImpl {

    private final UnmapperProxy unmapper;

    static ScopedMemoryAccess SCOPED_MEMORY_ACCESS = ScopedMemoryAccess.getScopedMemoryAccess();

    MappedMemorySegmentImpl(long min, UnmapperProxy unmapper, long length, int mask, MemoryScope scope) {
        super(min, length, mask, scope);
        this.unmapper = unmapper;
    }

    @Override
    ByteBuffer makeByteBuffer() {
        return nioAccess.newMappedByteBuffer(unmapper, min, (int)length, null, this);
    }

    @Override
    MappedMemorySegmentImpl dup(long offset, long size, int mask, MemoryScope scope) {
        return new MappedMemorySegmentImpl(min + offset, unmapper, size, mask, scope);
    }

    // mapped segment methods


    @Override
    public MappedMemorySegmentImpl asSlice(long offset, long newSize) {
        return (MappedMemorySegmentImpl)super.asSlice(offset, newSize);
    }

    @Override
    public MappedMemorySegmentImpl withAccessModes(int accessModes) {
        return (MappedMemorySegmentImpl)super.withAccessModes(accessModes);
    }

    @Override
    public boolean isMapped() {
        return true;
    }

    // support for mapped segments

    public MemorySegment segment() {
        return MappedMemorySegmentImpl.this;
    }

    public void load() {
        SCOPED_MEMORY_ACCESS.load(scope, min, unmapper.isSync(), length);
    }

    public void unload() {
        SCOPED_MEMORY_ACCESS.unload(scope, min, unmapper.isSync(), length);
    }

    public boolean isLoaded() {
        return SCOPED_MEMORY_ACCESS.isLoaded(scope, min, unmapper.isSync(), length);
    }

    public void force() {
        SCOPED_MEMORY_ACCESS.force(scope, unmapper.fileDescriptor(), min, unmapper.isSync(), 0, length);
    }

    // factories

    public static MemorySegment makeMappedSegment(Path path, long bytesOffset, long bytesSize, FileChannel.MapMode mapMode) throws IOException {
        Objects.requireNonNull(path);
        Objects.requireNonNull(mapMode);
        if (bytesSize < 0) throw new IllegalArgumentException("Requested bytes size must be >= 0.");
        if (bytesOffset < 0) throw new IllegalArgumentException("Requested bytes offset must be >= 0.");
        FileSystem fs = path.getFileSystem();
        if (fs != FileSystems.getDefault() ||
                fs.getClass().getModule() != Object.class.getModule()) {
            throw new IllegalArgumentException("Unsupported file system");
        }
        try (FileChannel channelImpl = FileChannel.open(path, openOptions(mapMode))) {
            UnmapperProxy unmapperProxy = ((FileChannelImpl)channelImpl).mapInternal(mapMode, bytesOffset, bytesSize);
            int modes = defaultAccessModes(bytesSize);
            if (mapMode == FileChannel.MapMode.READ_ONLY) {
                modes &= ~WRITE;
            }
            if (unmapperProxy != null) {
                MemoryScope scope = MemoryScope.createConfined(null, unmapperProxy::unmap, null);
                return new MappedMemorySegmentImpl(unmapperProxy.address(), unmapperProxy, bytesSize,
                        modes, scope);
            } else {
                return new EmptyMappedMemorySegmentImpl(modes);
            }
        }
    }

    private static OpenOption[] openOptions(FileChannel.MapMode mapMode) {
        if (mapMode == FileChannel.MapMode.READ_ONLY) {
            return new OpenOption[] { StandardOpenOption.READ };
        } else if (mapMode == FileChannel.MapMode.READ_WRITE || mapMode == FileChannel.MapMode.PRIVATE) {
            return new OpenOption[] { StandardOpenOption.READ, StandardOpenOption.WRITE };
        } else {
            throw new UnsupportedOperationException("Unsupported map mode: " + mapMode);
        }
    }

    static class EmptyMappedMemorySegmentImpl extends MappedMemorySegmentImpl {

        public EmptyMappedMemorySegmentImpl(int modes) {
            super(0, null, 0, modes,
                    MemoryScope.createConfined(null, MemoryScope.DUMMY_CLEANUP_ACTION, null));
        }

        @Override
        public void load() {
            // do nothing
        }

        @Override
        public void unload() {
            // do nothing
        }

        @Override
        public boolean isLoaded() {
            return true;
        }

        @Override
        public void force() {
            // do nothing
        }
    };
}