program won't end (resolved) & java.nio.file.AccessDeniedException on Windows

the following program will print done, but won’t end normally.

  def main(args: Array[String]): Unit = {
    val map1: Map[String, String, Nothing, ApiIO] = persistent.Map[String, String, Nothing, ApiIO]("map1").get
    map1.put("abc" -> "def", "123" -> "456").get
    map1.foreach(println)
      .materialize.get
    map1.close().get
    println("done")
  }

[simerplaha]

Closing this as it is resolved. Please reopen if needed.

[simerplaha]

This issue is now fixed in 0.14.6 release. All test-cases are passing on Windows 10. Please try re-running your code.

@Ectras you can now run your code without disabling mmap config.

Map<Integer, Integer, Void> map =
  MapConfig
    .functionsOff(Paths.get("data"), intSerializer(), intSerializer())
    .get();

map.put(42, 42);
System.out.println(map.get(42).get());

As mentioned before, the problem was that Windows does not allow deleting memory-mapped files unless the file’s in-memory MappedByteBuffer is cleared.

Solution

We now have a boolean cleanBeforeDelete flag in MMAP (memory-mapped) configuration. If cleanBeforeDelete is true then as the name says, memory-mapped files get cleaned before they are deleted which gets rid of the AccessDeniedException.

You don’t really have to learn these configurations at all because the default instances are already pre-configured and I will document these configurations on the website in detail but here is a basic overview if you are interested.

deleteAfterClean

In the following snippets deleteAfterClean is enabled if the operating system is Windows.

val mmap =
  MMAP.Enabled(
    deleteAfterClean = OperatingSystem.isWindows, //deleteAfterClean if OS is Windows
    forceSave = ForceSave.Disabled //disable ForceSave
  )

Java code looks like

MMAP.Enabled enabled =
  MMAP.enabled(
    OperatingSystem.isWindows(),
    ForceSave.disabled()
  );

ForceSave

ForceSave is a new configuration (#251). On Windows calling force on MappedByteBuffer is slower in certain situations (specially when copying memory-mapped) so this configuration was required. We can also disable force if we just want high performance and do not care about write guarantees on fatal machine crashes.

What is force?

force is just a function on MappedByteBuffer that “Forces any changes made to this buffer’s content to be written to the storage device containing the mapped file - JavaDoc”.

We can configure force to tell SwayDB when it should be invoked on files in any of the following 3 cases or we can disable it.

//tells SwayDB to invoke forceSave before closing a file
val beforeClose =
  ForceSave.BeforeClose(
    enableBeforeCopy = true, //also enable before copying a file
    enableForReadOnlyMode = false, //do not force save if the file is in read-only mode
    logBenchmark = true //log out time take to execute force
  )

//tells SwayDB to invoke forceSave before cleaning a memory-mapped file's MappedByteBuffer
val beforeClean =
  ForceSave.BeforeClean(
    enableBeforeCopy = true,
    enableForReadOnlyMode = true,
    logBenchmark = true
  )

//tells SwayDB to invoke forceSave before copying a file. This occurs during compaction
//where a file can simply be copied into another level without merge when there are no overlapping keys. 
val beforeCopy =
  ForceSave.BeforeCopy(
    enableForReadOnlyMode = true,
    logBenchmark = true
  )

//disables force save. 
val disabled =
  ForceSave.Disabled