[BCEL-267] Race conditions on static fields in BranchHandle and InstructionHandle

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 5.2
• Fix Version/s: 6.3.1
• Component/s: Main
• Flags: Patch
• Severity: normal
• Assignee: Unassigned
• Reporter: Stephan Herrmann
• Created: 29/Sep/15 20:12
• Updated: 12/Feb/19 23:00
• Resolved: 11/Feb/19 15:23

Description

I have observed race conditions causing NullPointerException like this

java.lang.NullPointerException
        at org.apache.bcel.generic.InstructionList.getInstructionHandles(InstructionList.java:1021)
        at org.apache.bcel.generic.InstructionList.findHandle(InstructionList.java:141)
        at org.apache.bcel.generic.MethodGen.<init>(MethodGen.java:194)

In the debugger I could verify that concurrent access to the fields BranchHandle.bh_list or InstructionHandle.ih_list can cause corruption of those lists.

I succeeded to make the exception less frequent by adding synchronized blocks, but still the exception could be observed. I concluded that for safe protection the fields would need to be made volatile, which in the end might actually defeat their original purpose of optimization.

I have since then run with a patched version of BCEL, where those static fields were simply removed and new Handles were created on every request. This variant finally was free of the race condition.

Seeing activity towards a 6.0 release, I'd appreciate if this change could be incorporated.

The original bug tracking my experiments can be found in Eclipse bugzilla: https://bugs.eclipse.org/344350

The modified classes (based on 5.2) can be found here:

• http://git.eclipse.org/c/objectteams/org.eclipse.objectteams.git/tree/plugins/org.eclipse.objectteams.otre/bcelpatchsrc/org/apache/bcel/generic

Issue Links

• duplicates: BCEL-105 Thread safety + unbuffered writes
• links to: GitHub Pull Request #23