[VFS-122] [vfs] Synchronization issue in SoftRefFilesCache

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.0
• Fix Version/s: 2.0

Environment

Sun Solaris, JDK 1.5.0_08

• Assignee: Unassigned
• Reporter: Raman Gupta
• Created: 04/Apr/07 06:17
• Updated: 27/Jul/16 21:04
• Resolved: 28/Dec/07 22:33

Description

I am using Commons VFS 1.0 RC8, and I believe I have found a
synchronization problem in SoftRefFilesCache.java. My system
occasionally exhibits high CPU usage in a thread with the stack shown
below [1]. The problem method is a HashMap.put at line 155 – though I
think the line number is actually 156, since 155 is a TreeMap.put.

Access to the refReverseMap is not synchronized (nor is the map itself
synchronized) which I believe is the problem. On multi-cpu machines,
this can cause race conditions in HashMap.

[1] Thread stack:

"Thread-28" prio=10 tid=0x00f56090 nid=0x34 runnable
[0xa787d000..0xa787f8f0]
at java.util.HashMap.put(HashMap.java:420)
at org.apache.commons.vfs.cache.SoftRefFilesCache.putFile(SoftRefFilesCache.java:155)

• locked <0xb7a09558> (a java.util.TreeMap)
  at org.apache.commons.vfs.provider.AbstractFileSystem.putFileToCache(AbstractFileSystem.java:163)
  at org.apache.commons.vfs.provider.AbstractFileSystem.resolveFile(AbstractFileSystem.java:306)
• locked <0xb791bfe8> (a org.apache.commons.vfs.provider.local.LocalFileSystem)
  at org.apache.commons.vfs.provider.AbstractFileSystem.resolveFile(AbstractFileSystem.java:264)
• locked <0xb791bfe8> (a org.apache.commons.vfs.provider.local.LocalFileSystem)
  at org.apache.commons.vfs.provider.AbstractFileSystem.getRoot(AbstractFileSystem.java:239)
  at org.apache.commons.vfs.provider.AbstractFileObject.getParent(AbstractFileObject.java:485)
  at org.apache.commons.vfs.provider.AbstractFileObject.isWriteable(AbstractFileObject.java:466)
  at org.apache.commons.vfs.provider.AbstractFileObject.getOutputStream(AbstractFileObject.java:1148)
  at org.apache.commons.vfs.provider.DefaultFileContent.getOutputStream(DefaultFileContent.java:367)
  at org.apache.commons.vfs.provider.DefaultFileContent.getOutputStream(DefaultFileContent.java:350)
  [...]