Mapped Memory Segment / Read from an existing file written via FileChannel or RandomAccessFile

[Johannes Lichtenberger]

Hello,

I'm currently not sure what I'm doing wrong, but the following test is not
working. Maybe it's too late, but I'm not sure if I'll have an immediate
idea tomorrow, so I guess it's best to ask for help :-)

kind regards
Johannes

import jdk.incubator.foreign.MemorySegment;
import jdk.incubator.foreign.ResourceScope;
import jdk.incubator.foreign.ValueLayout;
import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;

import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

import static org.junit.jupiter.api.Assertions.assertEquals;

public class TestFileChannelWithMemorySegment {

  private Path tempFile;

  @BeforeEach
  public void setup() {
    tempFile = Paths.get(System.getProperty("java.io.tmpdir"), "test.bin");
  }

  @AfterEach
  public void tearDown() throws IOException {
    Files.delete(tempFile);
  }

  @org.junit.jupiter.api.Test
  public void test() throws IOException {
//    try (final FileChannel fileChannel = FileChannel.open(tempFile,
//
StandardOpenOption.CREATE_NEW,
//
StandardOpenOption.WRITE)) {
//      final ByteBuffer byteBuffer = ByteBuffer.allocate(8);
//      byteBuffer.putLong(11);
//      byteBuffer.position(0);
//
//      fileChannel.write(byteBuffer);
//      fileChannel.force(true);
//    }

    try (final RandomAccessFile randomAccessFile = new
RandomAccessFile(tempFile.toFile(), "rw")) {
      randomAccessFile.writeLong(11);
    }

    try (final ResourceScope resourceScope = ResourceScope.newSharedScope()) {
      final MemorySegment memorySegment =
          MemorySegment.mapFile(tempFile, 0, Files.size(tempFile),
FileChannel.MapMode.READ_ONLY, resourceScope);

      final var longVal = memorySegment.get(ValueLayout.JAVA_LONG, 0);
      assertEquals(11, longVal);
    }
  }
}