RFR: 8254231: Implementation of Foreign Linker API (Incubator) [v18]

[Jorn Vernee]

On Wed, 11 Nov 2020 07:18:33 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Maurizio Cimadamore has updated the pull request incrementally with 10 additional commits since the last revision:
>> 
>>  - Merge pull request #7 from JornVernee/Additional_Review_Comments
>>    
>>    Additional review comments
>>  - Revert System.java changes
>>  - Set copyright year for added files to 2020
>>  - Check result of AttachCurrentThread
>>  - Sort includes alphabetically
>>  - Relax ret_addr_offset() assert
>>  - Extra space after if
>>  - remove excessive asserts in ProgrammableInvoker::invoke_native
>>  - Remove os::is_MP() check
>>  - remove blank line in thread.hpp
>
> src/hotspot/share/prims/universalUpcallHandler.cpp line 55:
> 
>> 53:     JavaVM_ *vm = (JavaVM *)(&main_vm);
>> 54:     jint result = vm->functions->AttachCurrentThread(vm, (void**) &p_env, nullptr);
>> 55:     guarantee(result == JNI_OK, "Could not attach thread for upcall. JNI error code: %d", result);
> 
> I'm assuming you don't have a mechanism for conveying an error back to the original entry point used by the native thread? Attaching an existing thread should only fail if we run out of C-Heap, so we're on the brink of aborting anyway, but still the guarantee here is not ideal.

Yeah, we have no idea where/how to report such and error. The native code might just call a function through a function pointer like `void(*)(void)` i.e. no place to return an error code. Also, since it's a previously non-attached thread, there is no JavaFrameAnchor that gives us a last Java frame we could jump back to and throw an exception.

Is there's a more explicit way to exit with an error, other than a `guarantee` that you would prefer here?

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

PR: https://git.openjdk.java.net/jdk/pull/634