perf: don't truncate separately over the file channel when writing, just specify the TRUNCATE_EXISTING OpenOption. It is much faster

Signed-off-by: Caleb Hulbert <cmhulbert@gmail.com>

Author: cmhulbert

src/main/java/org/janelia/saalfeldlab/n5/FsIoPolicy.java

@@ -45,7 +45,7 @@ static FileChannel openFileChannel(final Path path, final boolean forWriting) th
             if (parent != null) {
                 Files.createDirectories(parent);
             }
-            return FileChannel.open(path, StandardOpenOption.READ, StandardOpenOption.WRITE, StandardOpenOption.CREATE);
+            return FileChannel.open(path, StandardOpenOption.READ, StandardOpenOption.WRITE, StandardOpenOption.CREATE, StandardOpenOption.TRUNCATE_EXISTING);
         } else {
             return FileChannel.open(path, StandardOpenOption.READ);
         }

src/main/java/org/janelia/saalfeldlab/n5/LockedFileChannel.java

@@ -45,14 +45,12 @@ public InputStream newInputStream() throws N5Exception.N5IOException {
 	@Override
 	public Writer newWriter() throws N5Exception.N5IOException {
 
-		truncateChannel();
 		return Channels.newWriter(channel, StandardCharsets.UTF_8.name());
 	}
 
 	@Override
 	public OutputStream newOutputStream() throws N5Exception.N5IOException {
 
-		truncateChannel();
 		return Channels.newOutputStream(channel);
 	}
 
@@ -62,15 +60,6 @@ public FileChannel getFileChannel() {
 		return channel;
 	}
 
-	private void truncateChannel() throws N5Exception.N5IOException {
-
-		try {
-			channel.truncate(0);
-		} catch (final IOException e) {
-			throw new N5Exception.N5IOException("Failed to truncate channel", e);
-		}
-	}
-
 	@Override
 	public void close() throws IOException {