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https://issues.apache.org/jira/browse/IO-468?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14311673#comment-14311673
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Sebb commented on IO-468:
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I think the benchmark is not really the main issue here, although it will be
interesting to know whether or not ThreadLocal is quicker than memory
allocation, and for what buffer sizes.
Though of course that may change with different JVMs.
The point is that the patch has a side effect, which is that memory is held for
longer periods than may be necessary.
Also, it's not that allocation of the buffer is particularly slow, so even if
ThreadLocal is twice as fast, it's not going to make much difference to the
average app.
But it may make some apps with multiple threads use much more memory.
If the patch speeded up the code for all conditions, and had no side effects,
that would be different.
But that is not the case here.
Furthermore, an app that does rely heavily on the copy methods can provide the
appropriate buffers in order to gain a performance benefit.
But that will need to be tested in the context of the app itself to know
whether the trade-off between memory usage and allocation speed is worth it or
not.
I am against changing the existing methods.
Though I would be OK with adding Javadoc to note that the convenience methods
which provide their own buffers may in some cases be less efficient than using
buffers provided by the application.
> Avoid allocating memory for method internal buffers, use threadlocal memory
> instead
> -----------------------------------------------------------------------------------
>
> Key: IO-468
> URL: https://issues.apache.org/jira/browse/IO-468
> Project: Commons IO
> Issue Type: Improvement
> Components: Utilities
> Affects Versions: 2.4
> Environment: all environments
> Reporter: Bernd Hopp
> Priority: Minor
> Labels: newbie, performance
> Fix For: 2.5
>
> Attachments: PerfTest.java, monitoring_with_threadlocals.png,
> monitoring_without_threadlocals.png, performancetest.ods,
> performancetest_weakreference.ods
>
> Original Estimate: 12h
> Remaining Estimate: 12h
>
> In a lot of places, we allocate new buffers dynamically via new byte[]. This
> is a performance drawback since many of these allocations could be avoided if
> we would use threadlocal buffers that can be reused. For example, consider
> the following code from IOUtils.java, ln 2177:
> return copyLarge(input, output, inputOffset, length, new
> byte[DEFAULT_BUFFER_SIZE]);
> This code allocates new memory for every copy-process, that is not used
> outside of the method and could easily and safely reused, as long as is is
> thread-local. So instead of allocating new memory, a new utility-class could
> provide a thread-local bytearray like this:
> byte[] buffer = ThreadLocalByteArray.ofSize(DEFAULT_BUFFER_SIZE);
> return copyLarge(input, output, inputOffset, length, buffer);
> I have not measured the performance-benefits yet, but I would expect them to
> be significant, especially when the streams itself are not the performance
> bottleneck.
> Git PR is at https://github.com/apache/commons-io/pull/6/files
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