[jdk17] RFR: 8269865: Async UL needs to handle ERANGE on exceeding SEM_VALUE_MAX [v5]

[Xin Liu]

On Thu, 8 Jul 2021 22:12:23 GMT, Xin Liu <xliu at openjdk.org> wrote:

>> This patch solved the sempahore overflow issue with errno ERANGE or EOVERFLOW.
>> Previously, we have asymmetric p/v operations for semaphore _sem. Each iteration
>> only decrements _sem 1 but dequeues N messages. If logging threads keep preempting
>> async logging thread, it may cause the value of _sem accumulates until overflow! 
>> 
>> The patch corrects the value of _sem after write(). n messages are dequeued/processed.
>> We need to invoke _sem.wait() max(n-1, 1) time. This ensures that each iteration
>> decrements n instead of 1.
>
> Xin Liu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Refactor code with API change.
>   
>   Semaphore::signal returns a boolean value to indicate it's succeed or not.

Aha, os::PlatformMonitor is just the cross-platform condition variable, no strings attached!
I think it is a better solution. TBH,  I don't like 'ignore_overflow'. it's a hack solution. let's save it as a back-up solution. 

We still have 2 week before phase-2 rampdown.  Let me also take a look how JFR handle this case. It is said JFR also has an asynchronous buffer too.

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

PR: https://git.openjdk.java.net/jdk17/pull/216