RFR: 8343793: Test java/foreign/TestMemorySession.java is timing out

[Quan Anh Mai]

On Fri, 8 Nov 2024 11:56:08 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

> Hi,
> 
> This patch fixes the deadlock in `TestMemorySession#testAcquireCloseRace`. The lock-step spin lock is implemented as with `lock` being an `AtomicInteger`:
> 
>     // Keep the 2 threads operating on the same scope
>     int k = lock.getAndAdd(1) + 1;
>     while (k != i * 2) {
>         Thread.onSpinWait();
>         k = lock.get();
>     }
> 
> Given the initial condition:
> 
>     Thread 1: i = 0
>     Thread 2: i = 0
>     lock: -2
> 
> The `lock` then undergoes the following operations:
> 
> 
> 
>         Thread 1          Thread 2         lock value
>       getAndAdd(1)                            -1
>                         getAndAdd(1)           0 -> Thread 2 then continues its next iteration, its i value is now 1
>                         getAndAdd(1)           1 -> Thread 2 reaches the next iteration before thread 1 has a chance to read the value 0
>           get()                                1 -> Thread 1 now cannot proceed because it missed the value 0
>                            get()               1 -> Thread 2 now cannot proceed because lock can never reach 2
> 
> 
> The solution is to not rely on the exact value of the lock but instead whether the lock has passed the expected value.
> 
> Testing: I have run this test several hundreds times and got no failure while without this patch I encountered a timeout every approximately 30 times.
> 
> Please take a look, thanks a lot.

Sure, I have refactored the test, no failure after 200 runs.

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PR Comment: https://git.openjdk.org/jdk/pull/21976#issuecomment-2465276187