[crac] RFR: Provide arguments for restore [v5]

[Dan Heidinga]

On Thu, 17 Mar 2022 19:20:50 GMT, Anton Kozlov <akozlov at openjdk.org> wrote:

>> This change adds an ability to receive a new set of command-line arguments in the restored Java instance. The supplied demo code shows a faster replacement for `javac`.
>
> Anton Kozlov has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Use System class loader
>  - Make catch() preceise

src/java.base/share/classes/jdk/crac/Core.java line 177:

> 175:                          InvocationTargetException |
> 176:                          NoSuchMethodException     |
> 177:                          IllegalAccessException e) {

Thanks for adapting this to be more specific on what it catches.

I don't think it's quite right yet though as the current code will allow exceptions thrown by the `newMain` method (and its callees) to propagate past the checkpoint spot and makes the caller of the checkpoint code need to handle them.  

At the time `Core.checkpointRestore();` is called, we may have stack that looks llike:

TOS
Core.checkpointRestore();
Foo.bar();
Foo.foobar();
SomeOtherClass.method();
OriginalClass.main();


And when we restore, we load an execute a new `main()` method as though it was called where `Core.checkpointRestore();` was previously on the stack resulting in:

TOS
newMain.main();
Core.checkpointRestore();
Foo.bar();
Foo.foobar();
SomeOtherClass.method();
OriginalClass.main();


So exceptions thrown by code called from `newMain` should not propagate past `Core.checkpointRestore();` without being wrapped in a `RestoreException`.  `Error`-subclasses should propagate.

I think the code should be refactored to something like:

               } catch(Exception t) {
                   assert checkpointException == null :
                        "should not have new arguments";
                    if (restoreException == null) {
                        restoreException = new RestoreException();
                    }
                    restoreException.addSuppressed(e);
                }

as that correctly catches all Exceptions but lets the Errors propagate past

-------------

PR: https://git.openjdk.java.net/crac/pull/16