[TRINIDAD-2287] atomicity violation bugs of misusing concurrent collections

• Type: Bug
• Status: Patch Available
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.0.1-core
• Assignee: Unassigned
• Reporter: Yu Lin
• Created: 11/Jul/12 02:30
• Updated: 11/Jul/12 19:43

Description

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.