Async reading in FileSystemDataVault

CHANGELOG.unreleased.md

@@ -27,12 +27,13 @@ For upgrade instructions, please check the [migration guide](MIGRATIONS.released
 - Migrated nightly screenshot tests from CircleCI to GitHub actions. [#8134](https://github.com/scalableminds/webknossos/pull/8134)
 - Migrated nightly screenshot tests for wk.org from CircleCI to GitHub actions. [#8135](https://github.com/scalableminds/webknossos/pull/8135)
 - Thumbnails for datasets now use the selected mapping from the view configuration if available. [#8157](https://github.com/scalableminds/webknossos/pull/8157)
+- Reading image files on datastore filesystem is now done asynchronously. [#8126](https://github.com/scalableminds/webknossos/pull/8126)
 
 ### Fixed
 - Fixed a bug during dataset upload in case the configured `datastore.baseFolder` is an absolute path. [#8098](https://github.com/scalableminds/webknossos/pull/8098) [#8103](https://github.com/scalableminds/webknossos/pull/8103)
 - Fixed bbox export menu item [#8152](https://github.com/scalableminds/webknossos/pull/8152)
 - When trying to save an annotation opened via a link including a sharing token, the token is automatically discarded in case it is insufficient for update actions but the users token is. [#8139](https://github.com/scalableminds/webknossos/pull/8139)
-- Fix that scrolling in the trees and segments tab did not work while dragging. [#8162](https://github.com/scalableminds/webknossos/pull/8162) 
+- Fix that scrolling in the trees and segments tab did not work while dragging. [#8162](https://github.com/scalableminds/webknossos/pull/8162)
 - Fixed that uploading a dataset which needs a conversion failed when the angstrom unit was configured for the conversion. [#8173](https://github.com/scalableminds/webknossos/pull/8173)
 - Fixed that the skeleton search did not automatically expand groups that contained the selected tree [#8129](https://github.com/scalableminds/webknossos/pull/8129)
 - Fixed interactions in the trees and segments tab like the search due to a bug introduced by [#8162](https://github.com/scalableminds/webknossos/pull/8162). [#8186](https://github.com/scalableminds/webknossos/pull/8186)

webknossos-datastore/app/com/scalableminds/webknossos/datastore/datavault/FileSystemDataVault.scala

@@ -1,15 +1,16 @@
 package com.scalableminds.webknossos.datastore.datavault
 
 import com.scalableminds.util.tools.Fox
-import net.liftweb.common.Box.tryo
-import com.scalableminds.util.tools.Fox.{bool2Fox, box2Fox}
+import com.scalableminds.util.tools.Fox.bool2Fox
 import com.scalableminds.webknossos.datastore.storage.DataVaultService
+import net.liftweb.common.{Box, Full}
 import org.apache.commons.lang3.builder.HashCodeBuilder
 
 import java.nio.ByteBuffer
-import java.nio.file.{Files, Path, Paths}
+import java.nio.channels.{AsynchronousFileChannel, CompletionHandler}
+import java.nio.file.{Files, Path, Paths, StandardOpenOption}
 import java.util.stream.Collectors
-import scala.concurrent.ExecutionContext
+import scala.concurrent.{ExecutionContext, Promise}
 import scala.jdk.CollectionConverters._
 
 class FileSystemDataVault extends DataVault {
@@ -24,31 +25,55 @@ class FileSystemDataVault extends DataVault {
   private def readBytesLocal(localPath: Path, range: RangeSpecifier)(implicit ec: ExecutionContext): Fox[Array[Byte]] =
     if (Files.exists(localPath)) {
       range match {
-        case Complete() => tryo(Files.readAllBytes(localPath)).toFox
+        case Complete() =>
+          readAsync(localPath, 0, Math.toIntExact(Files.size(localPath)))
+
         case StartEnd(r) =>
-          tryo {
-            val channel = Files.newByteChannel(localPath)
-            val buf = ByteBuffer.allocateDirect(r.length)
-            channel.position(r.start)
-            channel.read(buf)
-            buf.rewind()
-            val arr = new Array[Byte](r.length)
-            buf.get(arr)
-            arr
-          }.toFox
+          readAsync(localPath, r.start, r.length)
+
         case SuffixLength(length) =>
-          tryo {
-            val channel = Files.newByteChannel(localPath)
-            val buf = ByteBuffer.allocateDirect(length)
-            channel.position(channel.size() - length)
-            channel.read(buf)
-            buf.rewind()
-            val arr = new Array[Byte](length)
-            buf.get(arr)
-            arr
-          }.toFox
+          val fileSize = Files.size(localPath)
+          readAsync(localPath, fileSize - length, length)
       }
-    } else Fox.empty
+    } else {
+      Fox.empty
+    }
+
+  private def readAsync(path: Path, position: Long, length: Int)(implicit ec: ExecutionContext): Fox[Array[Byte]] = {
+    val promise = Promise[Box[Array[Byte]]]()
+    val buffer = ByteBuffer.allocateDirect(length)
+    var channel: AsynchronousFileChannel = null
+
+    try {
+      channel = AsynchronousFileChannel.open(path, StandardOpenOption.READ)
+
+      channel.read(
+        buffer,
+        position,
+        buffer,
+        new CompletionHandler[Integer, ByteBuffer] {
+          override def completed(result: Integer, buffer: ByteBuffer): Unit = {
+            buffer.rewind()
+            val arr = new Array[Byte](length)
+            buffer.get(arr)
+            promise.success(Full(arr))
+            channel.close()
+          }
+
+          override def failed(exc: Throwable, buffer: ByteBuffer): Unit = {
+            promise.failure(exc)
+            channel.close()
+          }
+        }
+      )
+    } catch {
+      case e: Throwable =>
+        promise.failure(e)
+        if (channel != null && channel.isOpen) channel.close()
+    }
+
+    promise.future
+  }
 
   override def listDirectory(path: VaultPath, maxItems: Int)(implicit ec: ExecutionContext): Fox[List[VaultPath]] =
     vaultPathToLocalPath(path).map(