From colm.divilly at oracle.com  Wed Apr 24 13:50:57 2024
From: colm.divilly at oracle.com (Colm Divilly)
Date: Wed, 24 Apr 2024 13:50:57 -0000
Subject: Try with resources when exception raised in block and close() method
 on resource rethrows same exception instance
Message-ID: <IA0PR10MB7256598BAFA14408A6C63B53EB102@IA0PR10MB7256.namprd10.prod.outlook.com>

Hi,
In section 14.20.3.1 of the JLS [1] it is stated:

The meaning of a basic try-with-resources statement of the form:

try ({VariableModifier} R VariableDeclaratorId = Expression ...)
    Block

is given by the following translation to a local variable declaration and a try-catch-finally statement:

{
    final {VariableModifierNoFinal} R Identifier = Expression;
    Throwable #primaryExc = null;

    try ResourceSpecification_tail
        Block
    catch (Throwable #t) {
        #primaryExc = #t;
        throw #t;
    } finally {
        if (Identifier != null) {
            if (#primaryExc != null) {
                try {
                    Identifier.close();
                } catch (Throwable #suppressedExc) {
                    #primaryExc.addSuppressed(#suppressedExc);
                }
            } else {
                Identifier.close();
            }
        }
    }
}

I am wondering why the block:

                } catch (Throwable #suppressedExc) {
                    #primaryExc.addSuppressed(#suppressedExc);
                }

Does not guard against the possibility that #primaryExc == #suppressedExc?

If #primaryExc == #suppressedExc then addSuppressed will raise an IllegalArgumentException [2]

Whilst unusual for the close method to rethrow the exact same exception instance, I can?t see any reason that this would be prohibited, and so the block should probably look like:

                } catch (Throwable #suppressedExc) {
                    If (#suppressedExc != #primaryExc ) {
                        #primaryExc.addSuppressed(#suppressedExc);
                    }
                }
Regards,
Colm Divilly

[1]: https://docs.oracle.com/javase/specs/jls/se22/html/jls-14.html#jls-14.20.3.1
[2]: https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/lang/Throwable.java#L1123

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