RFR: 8316969: Improve CDS module graph support for --module option [v3]

[Alan Bateman]

On Thu, 19 Oct 2023 15:21:55 GMT, Calvin Cheung <ccheung at openjdk.org> wrote:

>> Please review this changeset for adding support for `--module` (-m) option for CDS.
>> Changes in the `ModuleBootstrap.java` are needed so that the `ArchivedModuleGraph.archive` and `ArchivedBootLayer.archive` are called if the main module is specified. The module name will be stored in the ro region of the CDS archive. During runtime, the archived module name will be compared with the runtime module name. If comparison fails, the archived full module graph won't be used.
>> 
>> Note: this RFE is a subtask of [JDK-8266329](https://bugs.openjdk.org/browse/JDK-8266329). More subtask(s) will be created to support other options such as `--add-modules`.
>> 
>> Passed tiers 1 - 4 testing.
>
> Calvin Cheung has updated the pull request incrementally with one additional commit since the last revision:
> 
>   simplify some code in modules.cpp

src/java.base/share/classes/jdk/internal/module/ModuleBootstrap.java line 481:

> 479:                     canArchive = true;
> 480:                 }
> 481:             }

An alternative to avoid the 3 levels of if expressions is to use:

        String scheme = systemModuleFinder.find(mainModule)
                .stream()
                .map(ModuleReference::location)
                .flatMap(Optional::stream)
                .findAny()
                .map(URI::getScheme)
                .orElse(null);
        if ("jrt".equalsIgnoreCase(scheme)) {
            canArchive = true;
        }

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

PR Review Comment: https://git.openjdk.org/jdk/pull/16016#discussion_r1367104266