[
https://issues.apache.org/jira/browse/TRINIDAD-2287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13411646#comment-13411646
]
Yu Lin commented on TRINIDAD-2287:
----------------------------------
Thanks for the confirmation. However, there are 17 such usages, and do you mean
none of them care about put-if-absent semantics? (I'm not sure about this
because I'm not an expert about this project).
In Cache.java and RenderKitBase.java, there are synchronization which prevents
concurrently write to the concurrent hash map. Can we remove those
synchronizations by using "putIfAbsent" or "replace" operations?
> 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.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators:
https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira
