Core: Lazily compute & cache hashCode in CharSequenceWrapper #10023
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| @Override | ||
| public int hashCode() { | ||
| return JavaHashes.hashCode(wrapped); | ||
| int hash = hashCode; |
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this uses a local hash var on purpose due to https://jeremymanson.blogspot.com/2008/12/benign-data-races-in-java.html. Also the String class itself uses the same approach when lazily calculating and caching a hashCode
| private JavaHashes() {} | ||
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| public static int hashCode(CharSequence str) { | ||
| if (null == str) { |
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there are places in the codebase that use CharSequenceWrapper.wrap(...) and then set the wrapper to null. The issue was never uncovered because equals/hashCode was never called on those CharSequenceWrapper instances.
When adding TestCharSequenceWrapper I noticed that this failed with a NPE, so I fixed this here and also added some tests around this
| public class TestCharSequenceWrapper { | ||
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| @Test | ||
| public void nullWrapper() { |
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this test uncovered a NPE in JavaHashes
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| private CharSequence wrapped; | ||
| // lazily computed & cached hashCode | ||
| private transient int hashCode = 0; |
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Hmm, I'm not sure I'd set a default value of 0, since that technically can be a legit hashCode value for some series of characters no?
I think I'd make this an Integer hashCode and have it be null to identify that nothing is cached yet.
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But good call making it transient, that's important since it shouldn't be serialized and the cache somehow used across JVMs
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I went down this rabbit hole: https://stackoverflow.com/questions/18746394/can-a-non-empty-string-have-a-hashcode-of-zero
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ah good point, thanks for finding that. Instead of making this an Integer I actually introduced a boolean flag. The String implementation does the same thing so that the hash isn't re-calculated when the hash is actually 0
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Awesome, maybe just comment in the code that we're following what java.lang.String does
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good point, I've added a comment mentioning that this follows java.lang.String
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amogh-jahagirdar
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This looks great to me!
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| private CharSequence wrapped; | ||
| // lazily computed & cached hashCode | ||
| private transient int hashCode = 0; |
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Awesome, maybe just comment in the code that we're following what java.lang.String does
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