Relaxed inUse definition

src/main/java/org/cryptomator/frontend/fuse/OpenFile.java

@@ -19,11 +19,19 @@ public class OpenFile implements Closeable {
 	private final Path path;
 	private final FileChannel channel;
 
+	/**
+	 * Whether any data has been changed on this file.
+	 *
+	 * This value only changes while holding a write lock, see {@link org.cryptomator.frontend.fuse.locks.LockManager}.
+	 */
+	private volatile boolean dirty;
+
 	private OpenFile(Path path, FileChannel channel) {
 		this.path = path;
 		this.channel = channel;
+		this.dirty = false;
 	}
-	
+
 	static OpenFile create(Path path, Set<? extends OpenOption> options, FileAttribute<?>... attrs) throws IOException {
 		FileChannel ch = FileChannel.open(path, options, attrs);
 		return new OpenFile(path, ch);
@@ -69,6 +77,7 @@ public int read(ByteBuffer buf, long num, long offset) throws IOException {
 	 * @throws IOException If an exception occurs during write.
 	 */
 	public int write(ByteBuffer buf, long num, long offset) throws IOException {
+		dirty = true;
 		if (num > Integer.MAX_VALUE) {
 			throw new IOException("Requested too many bytes");
 		}
@@ -80,13 +89,24 @@ public int write(ByteBuffer buf, long num, long offset) throws IOException {
 		return written;
 	}
 
+	/**
+	 * Tests, if this OpenFile is <em>dirty</em>.
+	 * An OpenFile is dirty, if its write method is called at least once.
+	 *
+	 * @return {@code true} if {@link OpenFile#write(ByteBuffer, long, long)} was called on this object, otherwise {@code false}
+	 */
+	boolean isDirty() {
+		return dirty;
+	}
+
 	@Override
 	public void close() throws IOException {
 		channel.close();
 	}
 
 	public void fsync(boolean metaData) throws IOException {
 		channel.force(metaData);
+		dirty = false;
 	}
 
 	public void truncate(long size) throws IOException {

src/main/java/org/cryptomator/frontend/fuse/OpenFileFactory.java

@@ -67,8 +67,15 @@ public void close(long fileHandle) throws ClosedChannelException, IOException {
 		}
 	}
 
-	public int getOpenFileCount(){
-		return openFiles.size();
+	/**
+	 * Tests, if any {@link OpenFile} is considered <em>dirty</em>, e.g. might have pending changes.
+	 * This method is neither atomic regarding the set of OpenFiles nor regarding each OpenFile individually. Therefore, external synchronization is required.
+	 *
+	 * @return {@code true} if and only if at least one dirty {@link OpenFile} exists. Otherwise {@code false}.
+	 * @see OpenFile#isDirty()
+	 */
+	boolean hasDirtyFiles() {
+		return openFiles.entrySet().stream().anyMatch(entry -> entry.getValue().isDirty());
 	}
 
 	/**

src/main/java/org/cryptomator/frontend/fuse/ReadOnlyAdapter.java

@@ -32,7 +32,6 @@
 import java.util.Collections;
 import java.util.EnumSet;
 import java.util.Set;
-import java.util.function.BooleanSupplier;
 
 public sealed class ReadOnlyAdapter implements FuseNioAdapter permits ReadWriteAdapter {
 
@@ -48,7 +47,6 @@ public sealed class ReadOnlyAdapter implements FuseNioAdapter permits ReadWriteA
 	private final ReadOnlyDirectoryHandler dirHandler;
 	private final ReadOnlyFileHandler fileHandler;
 	private final ReadOnlyLinkHandler linkHandler;
-	private final BooleanSupplier hasOpenFiles;
 
 	protected ReadOnlyAdapter(Errno errno, Path root, int maxFileNameLength, FileNameTranscoder fileNameTranscoder, FileStore fileStore, OpenFileFactory openFiles, ReadOnlyDirectoryHandler dirHandler, ReadOnlyFileHandler fileHandler) {
 		this.errno = errno;
@@ -61,7 +59,6 @@ protected ReadOnlyAdapter(Errno errno, Path root, int maxFileNameLength, FileNam
 		this.dirHandler = dirHandler;
 		this.fileHandler = fileHandler;
 		this.linkHandler = new ReadOnlyLinkHandler(fileNameTranscoder);
-		this.hasOpenFiles = () -> openFiles.getOpenFileCount() != 0;
 	}
 
 	public static ReadOnlyAdapter create(Errno errno, Path root, int maxFileNameLength, FileNameTranscoder fileNameTranscoder) {
@@ -305,7 +302,7 @@ public void destroy() {
 	@Override
 	public boolean isInUse() {
 		try (PathLock pLock = lockManager.tryLockForWriting("/")) {
-			return hasOpenFiles.getAsBoolean();
+			return openFiles.hasDirtyFiles();
 		} catch (AlreadyLockedException e) {
 			return true;
 		}