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https://issues.apache.org/jira/browse/IO-892?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18099423#comment-18099423
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Gary D. Gregory commented on IO-892:
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The observer already supports a {{FileFilter}}. Have you considering
implementing this as a new {{FileFilter}}? See the package
{{org.apache.commons.io.filefilter}}.
> Add maximum traversal depth to FileAlterationObserver
> -----------------------------------------------------
>
> Key: IO-892
> URL: https://issues.apache.org/jira/browse/IO-892
> Project: Commons IO
> Issue Type: New Feature
> Reporter: Xu Zhao
> Priority: Major
>
> FileAlterationObserver currently traverses the complete directory tree during
> both initialization and every checkAndNotify() cycle. This can cause
> significant I/O, allocation, sorting, and retained-memory overhead when the
> observed tree contains directories with hundreds of thousands of entries.
> This proposal adds an optional maximum traversal depth through
> FileAlterationObserver.Builder.setMaxDepth(int).
> Proposed semantics:
> * The observed root directory has depth 0.
> * A maximum depth of 0 prevents listing entries below the root.
> * At greater depths, entries at the maximum depth are monitored.
> * Children of entries at the maximum depth are not listed and do not generate
> events.
> * The default is Integer.MAX_VALUE, preserving the current recursive behavior.
> * Negative values are rejected with IllegalArgumentException.
> The depth limit applies consistently during initialization and every
> subsequent checkAndNotify() cycle.
> The change is source and binary compatible because existing constructors and
> Builder usage retain unlimited recursion by default.
> Local Windows/NTFS measurements with 100,000 empty files below a depth-1
> boundary:
> || Mode || Initialization || Steady check average ||
> | Unlimited | 9069.894 ms | 8772.802 ms |
> | maxDepth=1 | 126.719 ms | 16.517 ms |
> The implementation includes tests for default compatibility, invalid values,
> depth boundaries, ignored events below the boundary, repeated check cycles,
> custom root entries, direct listFiles() invocation checks, and serialization
> round trips.
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