BitronixTransactionManager.resume() gradually slower when called very often

Sometimes it is necessary to suspend/resume a Transaction very often.
If there is already at least one XaResource enlisted,
then resuming takes gradually longer as the size of the collection passed to CollectionUtils#containsByIdentity()
increments with each resume call and the collection is scanned sequentially (bad scalibility):

bitronix.tm.utils.CollectionUtils.java:
public static boolean containsByIdentity(Collection collection, Object toBeFound) {
Iterator it = collection.iterator();
while (it.hasNext())

return false;
}

Here a little testcase with his output:

// begin a transaction and enlist at least one XAResource
for (int i=0; i < 10; i++) {
long start = System.currentTimeMillis();
for (int j=0; j < 3000; j++)

long end = System.currentTimeMillis();
System.out.println(i + ".round: toke " + (end-start) + " ms for 3000 suspend + resume actions");
}

0.round: toke 1227 ms for 3000 suspend + resume actions
1.round: toke 2884 ms for 3000 suspend + resume actions
2.round: toke 4707 ms for 3000 suspend + resume actions
3.round: toke 7407 ms for 3000 suspend + resume actions
4.round: toke 9291 ms for 3000 suspend + resume actions
5.round: toke 10972 ms for 3000 suspend + resume actions
6.round: toke 12832 ms for 3000 suspend + resume actions
7.round: toke 15243 ms for 3000 suspend + resume actions
8.round: toke 17569 ms for 3000 suspend + resume actions
9.round: toke 17778 ms for 3000 suspend + resume actions

As you can see, the suspend/resume actions gradually get slower.

I suggest to change the collection implementation in order that a contains call
does not sequentially scan the entries.

How I discovered this:
Due a bug in Infinispan 4.00.CR3 (http://opensource.atlassian.com/projects/hibernate/browse/HHH-4836)
each infinispan-cache-put action did implicitly suspend/resume the current Transaction,
so I reached a number of 10.000 suspend/resume-actions within one single Transaction,
with very bad performance. Due jstack I discovered the bottleneck in containsByIdentity method.