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https://issues.apache.org/jira/browse/IO-271?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13029703#comment-13029703
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Stephen Kestle commented on IO-271:
-----------------------------------
I created a main method which will create a Thread that will either {{list()}}
or {{listFiles()}} for 500,000 files under the following conditions:
* the full canonical directory
* the relative "log" directory when running main from my application dir
* the "." directory when running main from my application's log dir
{{list()}} required a constant {{-Xmx41m}} for all invocations
{{listFiles()}} required:
* 91MB for "."
* 94MB for "log" (which is 3 chars * 2 bytes * 2 copies * 500000 = 3MB
difference)
* A whopping 181MB for the full canonical Program Files path (which is the most
likely path we'd be using)
_Note that the jvm needs somewhere between 1000-1500k to launch_
So the memory usage is something like 4.5 times which I think is significant
enough to fix.
I'd suggest that when the file filter is {{null}} that {{list()}} is used, and
when it a filter is given, use {{list(FileNameFilter)}} where the filter:
# takes the string
# creates a file object
# delegates to the given {{FileFilter}}
# throws away the File and accepts or rejects the String based on the
{{FileFilter}} result
Extra for experts (that's you guys :)); switch the above FileFilter behaviour
based on the amount of free memory in the system when processing the files by
retaining the {{File}} array, starting memory stats and a count etc. That is,
if memory's getting low, and the number of Files in the (Object) array high,
run through and replace the Files with their name, and continue by name.
> FileUtils.copyDirectory should be able to handle arbitrary number of files
> --------------------------------------------------------------------------
>
> Key: IO-271
> URL: https://issues.apache.org/jira/browse/IO-271
> Project: Commons IO
> Issue Type: Improvement
> Components: Utilities
> Affects Versions: 2.0.1
> Reporter: Stephen Kestle
> Priority: Minor
>
> File.listFiles() uses up to a bit over 2 times as much memory as File.list().
> The latter should be used in doCopyDirectory where there is no filter
> specified.
> This memory usage is a problem when copying directories with hundreds of
> thousands of files.
> I was also thinking of the option of implementing a file filter (that could
> be composed with the inputted filter) that would batch the file copy
> operation; copy the first 10000 (that match), then the next 10000 etc etc.
> Because of the lack of ordering consistency (between runs) of
> File.listFiles(), there would need to be a final file filter that would
> accept files that have not successfully been copied.
> I'm primarily concerned about copying into an empty directory (I validate
> this beforehand), but for general operation where it's a merge, the
> modification date re-writing should only be done in the final run of copies
> so that while batching occurs (and indeed the final "missed" filtering) files
> do not get copied if they have been modified after the start time. (I presume
> that I'm reading FileUtils correctly in that it overrides files...)
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