RFR: 8286597: Implement PollerProvider on AIX [v11]

[Alan Bateman]

On Tue, 23 May 2023 23:15:30 GMT, Tyler Steele <tsteele at openjdk.org> wrote:

>> This PR finalizes VThreads on AIX. After the heavy lifting was done by the lovely reinrich, all that remained was to implement the abstract methods in the Poller class. This was quite straightforward after I figured out that the Pollset library does not pick up on changes to the set of fds while blocked on a poll call.
>> 
>> ### Notes
>> 
>> As mentioned above, the Pollset library won't recognize changes made to the set of fds while blocked on a call to `poll`. In order to allow the other threads to make changes to the pollset, I had to set a short (max 100ms) timeout for the call to poll in order to ensure that the pollset is refreshed. In my testing, this was a far more reliable solution than using a wakeup fd. 
>> 
>> I provided an empty implementation of two procedures in `src/hotspot/cpu/ppc/continuationHelper_ppc.inline.hpp` with some deductive work. Examining other implementations, I see they delegate this to `update_map_with_saved_link`. This is empty in `frame_ppc.inline.hpp`, so I concluded that there is nothing to do for the two continuationHelper procedures either. I wouldn't mind a second opinion on this choice.
>> 
>> The test `testSocketReadPeerClose2` in BlockingSocketOps was modified because setting so_linger doesn't cause an exception to be thrown on AIX. The underlying read call returns -1 as will other platforms, but instead of setting ECONNRESET, AIX just sets EAGAIN. I feel that this test may just not be feasible on AIX, and I've modified it accordingly.
>> 
>> I modified the timeout factor for the virtual/stress/Skynet.java test. This test passes without issue on my build & test system when run on its own, but when run as part of a test suite (eg. `make test TEST=jdk_loom`), it does not have enough time with the timeout previously specified in the test file.
>> 
>> ### Testing
>> 
>> The following tests were performed on AIX.
>> 
>> - [x] T1 tests
>> - [x] hotspot_loom w/ -XX:+VerifyContinuations
>> - [x] jdk_loom w/ -XX:+VerifyContinuations
>
> Tyler Steele has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - Complete change
>  - Fixup & Reword
>  - Remove allocate-per-poll

src/java.base/aix/classes/sun/nio/ch/PollsetPoller.java line 42:

> 40:     private final int setid;
> 41:     private final long pollBuffer;
> 42:     private static final int POLL_BUFFER_SIZE = 16;

16 seems very low. On the other platforms the equivalent is sized to read up to 256 or 512 events in one syscall but maybe there is a reason to choose this small number? You might need to run Helidon Nima or some other server using virtual threads to see the impact on this.

The name used on other platforms for the constant is "MAX_EVENTS_TO_POLL" to better reflect the usage.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/13452#discussion_r1203510637