[jira] [Created] (COLLECTIONS-770) ToString method is unresponsive after multiple SetUtils union calls

[Jira]

Thomas Bürli created COLLECTIONS-770:
----------------------------------------

             Summary: ToString method is unresponsive after multiple SetUtils 
union calls
                 Key: COLLECTIONS-770
                 URL: https://issues.apache.org/jira/browse/COLLECTIONS-770
             Project: Commons Collections
          Issue Type: Bug
    Affects Versions: 4.4
            Reporter: Thomas Bürli
         Attachments: SetUtilsTest.java, stackdump.txt

I had the following code and my application stopped responsing as soon the 
number of names for a userId got too big.
{code:java}
       Map<String, Set<String>> stringMap = new TreeMap<>();
        for (String name : names) {
            for (String userId : userIds) {
                stringMap.merge(userId, Collections.singleton(name), 
SetUtils::union);
            }
        }
{code}
I did some debugging and it occurs when the toString method of one the set is 
called. It looks like the issues is with the iterator of "SetUtils.SetView".

Here just the method I used to create test sets and in the attachment you find 
the full tests class and a stack dump. The execution time is growing 
exponentially with the numbers of times the SetUtils.union is called. So for 29 
elements it took 16 seconds to execute toString, and with 30 it took 32 seconds.

{code:java}
    @Test
    void setWith20Elements() {
        assertTimeout(ofSeconds(2), () -> createSet(30).toString());
    }

    Set<String> createSet(int number) {
        List<String> inputs = new ArrayList<>();
        for (int i = 0; i < number; i++) {
           inputs.add("Test"+ i);
        }

        Set<String> testSet = Collections.singleton("String1");

        for (String element : inputs) {
            Set<String> part = Collections.singleton(element);
            testSet = SetUtils.union(testSet,part);
        }

        return testSet;
    }
{code}
Thanks for your support



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