Bug 323444 [Undo] [Commands] java.util.ConcurrentModificationException when trying to get the undo history from a source viewer
I got the following exception once when attempting to get the undo history from a source viewer in my code. Looking at the implementation of this method, I cannot seem to see how this could occur since all access to this list in DefaultOperationHistory are synchronized. Maybe it is the creation of the iterator outside of the synchronized block? Note that I have been unable to reproduce this since I first saw it since it seems to be a rare race condition. Exception Stack Trace: java.util.ConcurrentModificationException at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372) at java.util.AbstractList$Itr.next(AbstractList.java:343) at org.eclipse.core.commands.operations.DefaultOperationHistory.filter(DefaultOperationHistory.java:558) at org.eclipse.core.commands.operations.DefaultOperationHistory.getUndoHistory(DefaultOperationHistory.java:843)
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/operations/DefaultOperationHistory.java
IUndoContext[] contexts = operation.getContexts();
			for (int i = 0; i < contexts.length; i++) {
				flushRedo(contexts[i]);
			}
		} else {
			
			operation.dispose();
		}
	}
	/**
	 * <p>
	 * Add the specified approver to the list of operation approvers consulted
	 * by the operation history before an undo or redo is allowed to proceed.
	 * This method has no effect if the instance being added is already in the
	 * list.
	 * </p>
	 * <p>
	 * Operation approvers must be prepared to receive these the operation
	 * approval messages from a background thread. Any UI access occurring
	 * inside the implementation must be properly synchronized using the
	 * techniques specified by the client's widget library.
	 * </p>
	 * 
	 * @param approver
	 *            the IOperationApprover to be added as an approver.
	 * 
	 */
	public void addOperationApprover(IOperationApprover approver) {
		approvers.add(approver);
	}