Fix AtomicFile FileNotFoundException when a namepace is being accessed concurrently.

[TonyTangAndroid]

This pull request aims to fix the FileNotFoundException triggered when the namespace being created and accessed concurrently for the first time.

Given the following sample code to create a PrimitiveSimpleStore instance,

        private fun dataStore(app: Application): PrimitiveSimpleStore {
            return PrimitiveSimpleStoreFactory.create(
                AndroidDirectoryProvider(app),
                "657b3cd7-f689-451b-aca0-628de60aa234",
                NamespaceConfig.CRITICAL
            )
        }

whenever PrimitiveSimpleStore#putString is executed for the first time, it will implicitly trigger the detected code in AtomicFile. At this time, the parent folder of mNewName is 657b3cd7-f689-451b-aca0-628de60aa234 and it is not created, hence, the first expectedFileNotFoundException is triggered. However, there could be two thread concurrently trigger such error, which leads both thread to execute the statement parent.mkdirs(), which results in either one of them failure in create directory.

To validate this theory, dedicated test code AtomicFileConcurrentTest has been written to reproduce the error and fix the issue.

  public FileOutputStream startWrite() throws IOException {
    if (mLegacyBackupName.exists()) {
      rename(mLegacyBackupName, mBaseName);
    }

    try {
      return new FileOutputStream(mNewName);
    } catch (FileNotFoundException e) {
      File parent = mNewName.getParentFile();
      if (!parent.mkdirs()) {
        throw new IOException("Failed to create directory for " + mNewName);
      }
      try {
        return new FileOutputStream(mNewName);
      } catch (FileNotFoundException e2) {
        throw new IOException("Failed to create new file " + mNewName, e2);
      }
    }
  }

For more details, please refer to the test code to highlight the difference.

One should be noted There are a lot of trial and error in the process of reproducing the issues and fixing the issue, it is recommended for the reviewers to squash all the commits as one commit when it is to be merged. This way, the commit history will remain to be clean.

[TonyTangAndroid]

Those are exactly the same code that are on PROD right now.

[TonyTangAndroid]

Those are the core code to make the fix effective. One should be noted that synchronized will only be applied when the folder was missing. If the folder is already present, then those piece of code will no longer be executed again.

[TonyTangAndroid]

Add comments to highlight the changes in fixing the FileNotFoundException

[TonyTangAndroid]

We are to conduct the clean up once we confirm the fix is effective or even apply the legacy branch again if we could figure out the higher level root cause.

[TonyTangAndroid]

Apply java.nio.file.Files.createDirectories

[TonyTangAndroid]

Abort this pull request for now to apply Files.createDirectories without concurrent fix