[BATIK-802] [PATCH] Race condition in CleanerThread.java getReferenceQueue() method

• Type: Bug
• Status: Open
• Resolution: Unresolved
• Affects Version/s: 1.8
• Component/s: Utilities
• Environment: Operating System: All; Platform: All
• Assignee: Unassigned
• Reporter: Archie Cobbs
• Created: 07/Jan/08 09:33
• Updated: 14/Aug/17 11:39

Description

In org.apache.batik.util.CleanerThread we see:

public static ReferenceQueue getReferenceQueue() {
if ( queue == null ) {
synchronized (CleanerThread.class)

{ queue = new ReferenceQueue(); thread = new CleanerThread(); }

}
return queue;
}

This method is not thread safe due to a race condition. The test for "if (queue
== null)" needs to be inside the synchronized block, not outside of it. As
written, it's possible for the initialization code to be executed more than once.

Fix: make the entire method synchronized, or add an additional test for "if
(queue == null)" within the synchronized block (but see
http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html for why
the variable needs to remain volatile).