Re: RFR: 8015831: Add lint check for calling overridable methods from a constructor [v5]

[Maurizio Cimadamore]

On Tue, 10 Jan 2023 19:20:35 GMT, Archie L. Cobbs <d...@openjdk.org> wrote:

>> src/jdk.compiler/share/classes/com/sun/tools/javac/comp/ThisEscapeAnalyzer.java
>>  line 1098:
>> 
>>> 1096:     private <T extends JCTree> void visitLooped(T tree, Consumer<T> 
>>> visitor) {
>>> 1097:         this.visitScoped(tree, false, t -> {
>>> 1098:             while (true) {
>> 
>> Why is this needed? Can the tracking state of `this` change after multiple 
>> "execution" of the same code?
>
> 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?

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PR: https://git.openjdk.org/jdk/pull/11874