Can access closed memory segment

[Maurizio Cimadamore]

Thanks Remi, we'll take a look

Maurizio

On 18/06/2024 08:54, Remi Forax wrote:
> Hello,
> I think i've found an issue in the current implementation of shared arena close(),
> when closing the scope the VM only checks if the arena is on stack but the memory segment can be stored in a static final.
>
> In the following code, i'm able to read the segment after the shared arena is closed.
>
> public class SharedArenaCloseBug {
>    static final Arena SHARED = Arena.ofShared();
>    static final MemorySegment SEGMENT = SHARED.allocate(16);
>    static int STATE;
>
>    void run() {
>      for(;;) {
>        if (STATE == 0) {
>          var value = SEGMENT.get(ValueLayout.JAVA_BYTE, 0L);
>          if (value == 42) {
>            return;
>          }
>        }
>      }
>    }
>
>    public static void main(String[] args) throws InterruptedException {
>      var bug = new SharedArenaCloseBug();
>      var thread = new Thread(bug::run);
>      thread.start();
>      Thread.sleep(100);
>      STATE = 1;
>      System.out.println("state 1");
>      Thread.sleep(100);
>      System.out.println("close");
>      SEGMENT.set(ValueLayout.JAVA_BYTE, 0L, (byte) 42);
>      SHARED.close();
>      Thread.sleep(100);
>      System.out.println("state 0");
>      STATE = 0;
>      Thread.sleep(100);
>      System.out.println("join");
>      thread.join();
>    }
> }
>
> regards,
> Rémi