RFR: 8259623: JfrTypeSet::_subsystem_callback is left dangling after use

[Markus Grönlund]

On Thu, 25 Mar 2021 13:15:26 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> SonarCloud instance reports the bug in cases like:
>   "Address of stack memory associated with local variable 'callback' is still referred to by the global variable '_subsystem_callback' upon returning to the caller. This will be a dangling reference"
> 
> For example:
> 
> static void clear_packages() {
>   ClearArtifact<PkgPtr> clear;
>   ClearPackageCallback callback(&clear);
>   _subsystem_callback = &callback;
>   do_packages();
> }
> 
> I understand that `_subsystem_callback` is assigned to be used in do_packages(), but it would indeed be left dangling. The patch moves callback installation into the callback superclass itself. This way, we also guarantee that `_subsystem_callback` is not set before installation (i.e. check for overlapping callback installations), and make sure it is `NULL` after use.

Looks good, Thanks.

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Marked as reviewed by mgronlun (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/3192