RFR: 8307944: ClassFileDumper should only load java.nio.file.Path if enabled

[Roger Riggs]

On Thu, 25 May 2023 20:23:27 GMT, Mandy Chung <mchung at openjdk.org> wrote:

> Change `ClassFileDumper` constructor to take a `String` rather than `Path` to avoid the file system implementation classes loaded during startup.  In addition, `FilePermission` also causes the default file system to be initialized. 
> 
> This patch changes `ClassFileDumper` to validate the given path only if it's enabled and not to use limited `doPrivileged` to avoid the initialization of `FilePermission` class and the file system implementation classes by default.
> 
> This patch also changes `ClassFileDumper::write` to use `File` instead of `Path` because of JDK-8306678.  `OperatingSystem::<clinit>` causes `Enum::valueOf` to be called which calls core reflection which in turns invokes method handles.   If `-Djdk.invoke.MethodHandle.dumpMethodHandleInternals` is set, VM initialization would fail because `BootLoader::<clinit>` causes `ClassLoaderHelper` to initialize which in turn causes `OperatingSystem` be initialized.   If additional LFs are spinned and dumped, if `ClassFileDumper` uses `Path` for writing, `FileSystems::getDefault` would fail with `NullPointerException` because it calls `BootLoader.loadLibrary` which is not fully initialized. 
> 
> A separate issue will be filed to follow up the startup overhead of `OperatingSystem`.

Looks good, delaying the checking of the file system until its is needed will save on startup.

src/java.base/share/classes/jdk/internal/util/ClassFileDumper.java line 136:

> 134:         // recursive initialization during early startup. e.g.
> 135:         // Enum::valueOf causes method handle to be invoked which
> 136:         // may cause classes to be spinned and dumped

This comment could be omitted; it won't age well and is out of context for the fix.

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Marked as reviewed by rriggs (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/14160#pullrequestreview-1444720329
PR Review Comment: https://git.openjdk.org/jdk/pull/14160#discussion_r1206049390