On Wed, 11 Jan 2023 00:04:14 GMT, Maurizio Cimadamore <mcimadam...@openjdk.org>
wrote:
>> Yes, because the 'this' reference can bounce around through different
>> variables in scope each time around the loop. So we have to repeat the loop
>> until all 'this' references have "flooded" into all the nooks and crannies.
>>
>> The `ThisEscapeLoop.java` unit test demonstrates:
>>
>> public class ThisEscapeLoop {
>>
>> public ThisEscapeLoop() {
>> ThisEscapeLoop ref1 = this;
>> ThisEscapeLoop ref2 = null;
>> ThisEscapeLoop ref3 = null;
>> ThisEscapeLoop ref4 = null;
>> for (int i = 0; i < 100; i++) {
>> ref4 = ref3;
>> ref3 = ref2;
>> ref2 = ref1;
>> if (ref4 != null)
>> ref4.mightLeak();
>> }
>> }
>>
>> public void mightLeak() {
>> }
>> }
>
> So, if the code was be like this:
>
>
> ThisEscapeLoop ref11 = this;
> ThisEscapeLoop ref12 = null;
> ThisEscapeLoop ref13 = null;
> ThisEscapeLoop ref14 = null;
> for (int i = 0; i < 100; i++) {
> ref14 = ref13;
> ref13 = ref12;
> ref12 = ref11;
> ThisEscapeLoop ref21 = ref14;
> ThisEscapeLoop ref22 = null;
> ThisEscapeLoop ref23 = null;
> ThisEscapeLoop ref24 = null;
> for (int i = 0; i < 100; i++) {
> ref24 = ref23;
> ref23 = ref22;
> ref22 = ref21;
> if (ref24 != null)
> ref24.mightLeak();
> }
> }
>
>
> Then it would take not 3 iterations but 3 * 3 to figure out that it is a
> potential leak?
Actually I think it would take 1 + 1 + 3 iterations.
During the first two iterations of the outer loop, nothing changes after the
first go round of the inner loop - i.e., the total set of possible references
in existence does not change, because all of the assignments in the inner loop
won't involve any 'this' references.
It's only the during the third iteration of the outer loop that any 'this'
references seep into any of the variables seen by the inner loop. Then it will
take 3 cycles for the reference set to converge again.
However, this is not to say that there aren't some pathological examples out
there. I guess the question is could they exist in "normal" code.
-------------
PR: https://git.openjdk.org/jdk/pull/11874
