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https://issues.apache.org/jira/browse/LUCENENET-495?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13393631#comment-13393631
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Christopher Currens commented on LUCENENET-495:
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I did fix the thread-safety bug. The code was checking if a key existed in the
(synchronized) HashTable, and then tried to add it. Because there was no
locking, there was the scenario when two threads would check if the key existed
at the same time, then both add it within a few instructions of each other,
causing one to throw an ArgumentException, because the key already existed.
In all of the code code, we are using the correct types we should be (I think).
This is code in the test suite that hasn't ever been updated. In fact, it
really should be a HashSet and not a HashTable. We were using it because at
the time, it was pre-.net 3.0, and the only way to match the java code. We
could change it, but IMO, it's not really worth it right now, because it's ONLY
used in the test code. In the next version we're porting, the testing code is
significantly different, so I don't want to spend _too_ much time cleaning it
up if it works.
> Use of DateTime.Now causes huge amount of System.Globalization.DaylightTime
> object allocations
> ----------------------------------------------------------------------------------------------
>
> Key: LUCENENET-495
> URL: https://issues.apache.org/jira/browse/LUCENENET-495
> Project: Lucene.Net
> Issue Type: Bug
> Components: Lucene.Net Core
> Affects Versions: Lucene.Net 2.9.4, Lucene.Net 3.0.3
> Reporter: Christopher Currens
> Assignee: Christopher Currens
> Priority: Critical
> Fix For: Lucene.Net 3.0.3
>
>
> This issue mostly just affects RAMDirectory. However, RAMFile and
> RAMOutputStream are used in other (all?) directory implementations, including
> FSDirectory types.
> In RAMOutputStream, the file last modified property for the RAMFile is
> updated when the stream is flushed. It's calculated using
> {{DateTime.Now.Ticks / TimeSpan.TicksPerMillisecond}}. I've read before that
> Microsoft has regretted making DateTime.Now a property instead of a method,
> and after seeing what it's doing, I'm starting to understand why.
> DateTime.Now is returning local time. In order for it to calculate that, it
> has to get the utf offset for the machine, which requires the creation of a
> _class_, System.Globalization.DaylightTime. This is bad for performance.
> Using code to write 10,000 small documents to an index (4kb sizes), it
> created 1,570,157 of these DaylightTime classes, a total of 62MB of extra
> memory...clearly RAMOutputStream.Flush() is called a lot.
> A fix I'd like to propose is to change the RAMFile from storing the
> LastModified date to UTC instead of local. DateTime.UtcNow doesn't create
> any additional objects and is very fast. For this small benchmark, the
> performance increase is 31%.
> I've set it to convert to local-time, when {{RAMDirectory.LastModified(string
> name)}} is called to make sure it has the same behavior (tests fail
> otherwise). Are there any other side-effects to making this change?
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