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https://issues.apache.org/jira/browse/TRINIDAD-2287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13411194#comment-13411194
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Blake Sullivan commented on TRINIDAD-2287:
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I don't understand why you think that no preserving put-if-absent semantics is
important. The code says that it explicitly doesn't care about these semantics:
// we don't need putIfAbsent because we don't care about identity
_sDefaultKeyCache.put(name, cachedKey);
Since we don't care about those semantics, put will always perform better than
putIfAbsent
> atomicity violation bugs of misusing concurrent collections
> -----------------------------------------------------------
>
> Key: TRINIDAD-2287
> URL: https://issues.apache.org/jira/browse/TRINIDAD-2287
> Project: MyFaces Trinidad
> Issue Type: Bug
> Affects Versions: 2.0.1-core
> Reporter: Yu Lin
> Attachments: trinidad-2.0.1.patch
>
> Original Estimate: 504h
> Remaining Estimate: 504h
>
> My name is Yu Lin. I'm a Ph.D. student in the CS department at
> UIUC. I'm currently doing research on mining Java concurrent library
> misusages. I found some misusages of ConcurrentHashMap in Trinidad
> 2.0.1, which may result in potential atomicity violation bugs or harm
> the performance.
> The code below is a snapshot of the code in file
> trinidad-api/src/main/java/org/apache/myfaces/trinidad/bean/PropertyKey.java
> from line 102 to 112
> L102 PropertyKey cachedKey = _sDefaultKeyCache.get(name);
> L104 if (cachedKey == null)
> L105 {
> L106 cachedKey = new PropertyKey(name);
> L108 // we don't need putIfAbsent because we don't care about identity
> L109 _sDefaultKeyCache.put(name, cachedKey);
> L110 }
> L112 return cachedKey;
> In the code above, an atomicity violation may occur between line 105
> and 109. Suppose a thread T1 executes line 102 and finds out the
> concurrent hashmap does not contain the key "name". Before it gets to
> execute line 109, another thread T2 puts a pair <name, v> in the
> concurrent hashmap "_sDefaultKeyCache". Now thread T1 resumes
> execution and it will overwrite the value written by thread T2. Thus,
> the code no longer preserves the "put-if-absent" semantics.
> I found some similar atomicity violations in other 17 places (I don't
> list them one by one. Please see the patch).
> Note that in
> trinidad-impl/src/main/java/org/apache/myfaces/trinidadinternal/image/cache/Cache.java,
> if we use "putIfAbsent" at line 89 and "replace" at line 115, we may
> remove the synchronized keyword at line 82. Similarly, in
> trinidad-impl/src/main/java/org/apache/myfaces/trinidadinternal/renderkit/RenderKitBase.java,
> we may remove the synchronized by using "putIfAbsent" at line 192.
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