RFR: 8334868: Ensure CheckUninstallModalHook is called in WPageDialogPeer._show

[Phil Race]

On Mon, 24 Jun 2024 20:16:30 GMT, Alexey Ivanov <aivanov at openjdk.org> wrote:

> This is somewhat a continuation for [JDK-8307160](https://bugs.openjdk.org/browse/JDK-8307160) and [JDK-8334509](https://bugs.openjdk.org/browse/JDK-8334509).
> 
> The former removed the `doIt` flag in #18584, but it introduced a regression.  
> The regression is resolved by the latter in #19786, and it added the 'doIt' flag again.
> 
> I think using a flag makes the code less clear. When reading the code, one has to keep track of the current value of the `doIt` flag.
> 
> I raised my concern in [comments in PR 19786](https://github.com/openjdk/jdk/pull/19786#discussion_r1649191308):
> 
>> I'd rather keep `JNI_FALSE` here — it's more explicit and therefore clearer. You don't have to keep track of the value of `doIt` flag while reading the code.
>> 
>> In fact, I'd prefer no `doIt` flag at all… yet it makes handling the code below `if (ret)` slightly harder.
> 
> I came up with a solution which simplifies handling the clean-up. The solution relies on C++ destructors which are called when the declared objects go out of scope.
> 
> The C++ object wraps a lambda function to clean up and invokes this function in its destructor. Such C++ class has to be a templated class because there's no defined type to represent a lambda. The class has to be declared at the top of the file because it needs C++ linkage.
> 
> There are two `Cleaner` objects declared in the code of `Java_sun_awt_windows_WPageDialogPeer__1show`:
> 
> **`refCleaner`** is declared right after all the references to Java objects are initialised. The corresponding `refCleanup` lambda deletes all the references and replaces the `CLEANUP_SHOW` macro. Before JDK-8307160, the code jumped to a go-to label to perform the clean-up.
> 
> **`postCleaner`** is declared after `AwtDialog::CheckInstallModalHook` is called. Its lambda `postCleanup` uninstalls the modal hook and handles focus transfer as well as saves the updated printer parameters.
> 
> It is `postCleaner` that resolves the bug JDK-8334868 by ensuring `CheckUninstallModalHook` and `ModalActivateNextWindow` are called if `::PageSetupDlg` is called.
> 
> As the result of using `refCleaner`, all the `return` statements in the function use an explicit value, which makes the code cleaner. There's no need to use a `go to` statement or insert a macro to delete references to Java objects, about which one had to remember — the destructor of the `refCleaner` handles deleting references when `refCleaner` goes out of scope, that is when the function returns.

Sorry, but I  don't see this as better or needed. I was the one who requested the current code  and I don't see the need for all this complexity.
Just do the minimum change to make sure we do CheckUninstallModalHook is called.

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Changes requested by prr (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/19867#pullrequestreview-2169910991