[GitHub] gianm commented on a change in pull request #6677: FileUtils: Sync directory entry too on writeAtomically.

[GitBox <gi...@apache.org>]

gianm commented on a change in pull request #6677: FileUtils: Sync directory entry too on writeAtomically.
URL: https://github.com/apache/incubator-druid/pull/6677#discussion_r239900652
 
 

 ##########
 File path: core/src/main/java/org/apache/druid/java/util/common/FileUtils.java
 ##########
 @@ -182,22 +187,34 @@ public static MappedByteBufferHandler map(File file) throws IOException
    *
    * This method is not just thread-safe, but is also safe to use from multiple processes on the same machine.
    */
-  public static void writeAtomically(final File file, OutputStreamConsumer f) throws IOException
+  public static <T> T writeAtomically(final File file, OutputStreamConsumer<T> f) throws IOException
   {
-    writeAtomically(file, file.getParentFile(), f);
+    return writeAtomically(file, file.getParentFile(), f);
   }
 
-  private static void writeAtomically(final File file, final File tmpDir, OutputStreamConsumer f) throws IOException
+  private static <T> T writeAtomically(final File file, final File tmpDir, OutputStreamConsumer<T> f) throws IOException
   {
     final File tmpFile = new File(tmpDir, StringUtils.format(".%s.%s", file.getName(), UUID.randomUUID()));
 
-    try {
-      try (final FileOutputStream out = new FileOutputStream(tmpFile)) {
+    //noinspection unused
+    try (final Closeable deleter = () -> java.nio.file.Files.deleteIfExists(tmpFile.toPath())) {
+      final T retVal;
+
+      try (
+          final FileChannel fileChannel = FileChannel.open(
+              tmpFile.toPath(),
+              StandardOpenOption.WRITE,
+              StandardOpenOption.CREATE_NEW
+          );
+          final OutputStream out = Channels.newOutputStream(fileChannel)
 
 Review comment:
   The `fileChannel.force` (fsync) has to be done while the stream is still open, so we can't close the OutputStream before that happens. So that's why the flush was first. I just pushed a change with some more comments describing what's going on.
   
   But, I also removed the `out.flush` completely in this commit -- Channels.newOutputStream is specced as unbuffered, so a flush isn't necessary.

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