RFR: 8319589: Attach from root to a user java process not supported in Mac [v8]

[Serguei Spitsyn]

On Fri, 5 Dec 2025 09:42:51 GMT, Sergey Chernyshev <schernyshev at openjdk.org> wrote:

>> We had a private discussion with Larry on this PR and undesired dependency on the `sun.jvmstat` module.
>> We got the following concerns:
>>  - Do we really need 3x implementations of the MacOS `tempdir` finder function?
>>  - Do we really need a modular dependency from `jdk.attach` to `jdk.internal.jvmstat`?
>> New method `getTemporaryDirectories(int pid)` is placed into the `jdk.internal.jvmstat/macosx/classes/sun/jvmstat/PlatformSupportImpl.java`. It seems it was needed to inherit the `PlatformSupport` class which has the method `PlatformSupport.getTemporaryDirectory()`. But it returns the same as the removed function `Java_sun_tools_attach_VirtualMachineImpl_getTempDir()`. So, this implementation can be moved to the `jdk.attach` module.
>> My understanding is that class `PlatformSupportImpl` and its method `getTemporaryDirectories(int pid)`  is not currently used for `jvmstat` implementation. Is it correct? Is it right that the `jvmstat` implementation still does not properly support root user on macOS?
>> Anyway, some unification and refactoring is needed here. We could file a follow up enhancement to sort this out but also wanted to know your opinion on this.
>
> Hi @sspitsyn ,
> 
> Thank you for looking at this patch!
> 
>> This is a nice fix in general. Thank you for this work! I hope to complete my review tomorrow with one more pass. Question: How was this update tested? Do you have a jtreg test or you've done it manually? Also, did you run mach5 tiers 1-6 to be safe and protected against regressions?
> 
> The patch was tested against the current jtreg test groups (tier1-3) on macOS both amd64 and arm64. I also run jcmd and jps tools manually under root, because the change only affects the behavior under root.
> 
>> * It seems it was needed to inherit the `PlatformSupport` class which has the method `PlatformSupport.getTemporaryDirectory()`. But it returns the same as the removed function `Java_sun_tools_attach_VirtualMachineImpl_getTempDir()`. So, this implementation can be moved to the `jdk.attach` module.
> 
> The removed function `Java_sun_tools_attach_VirtualMachineImpl_getTempDir()` would return always the same string cached inside the libsystem_coreservices.dylib, that would correspond the user specific temporary path as of how the JVM process has started, that would have nothing to do with the target process/pid temporary directory.
> 
>> * My understanding is that class `PlatformSupportImpl` and its method `getTemporaryDirectories(int pid)`  is not currently used for `jvmstat` implementation. Is it correct?
> 
> I think this is not exactly so. `getTemporaryDirectories(int pid)` is used currently in the LocalVmManager to get the list of active VMs, that is consumed by `jcmd`, `jps` and `jconsole` utilities. When 0 is passed as a parameter, it returns the list of temp directories for all processes, if they were different (for example if there are containerized JVM processes under Linux).
> 
>> * Is it right that the `jvmstat` implementation still does not properly support root user on macOS?
> 
> Yes and this is what this patch was intended for.
> 
>>     * Do we really need 3x implementations of the MacOS `tempdir` finder function?
> 
> It was already 2x implementation of HotSpot perfdata files lookup, HotSpot itself uses the `os::get_temp_directory()`, on the java side the LocalVmManager in `sun.jvmstat.perfdata.monitor` relies on `getTemporaryDirectories(int pid)` in the PlatformSupport. The 3rd was the macOS native `Java_sun_tools_attach_VirtualMachineImpl_getTempDir()`, now it's proposed for removal as it returns only the current user temp path, no matter what process is being attached to.
> 
>>     * Do we really need a modular dependency f...

@sercher Thank you for the readability updates and answering questions!

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PR Comment: https://git.openjdk.org/jdk/pull/25824#issuecomment-3631118258