Program crash: GC destroys an object unexpectedly

[Steven Schveighoffer]

On 9/14/21 7:31 AM, eugene wrote:
> On Monday, 13 September 2021 at 17:18:30 UTC, eugene wrote:
>> Then after pressing ^C (SIGINT) the program gets SIGSEGV, since 
>> references to sg0 and sg1 are no longer valid (they are "sitting" in 
>> epoll_event structure).
> 
> ... forget to mention, crashes here:
> 
> ```d
>      bool wait() {
> 
>          const int maxEvents = 8;
>          EpollEvent[maxEvents] events;
> 
>          if (done)
>              return false;
> 
>          int n = epoll_wait(id, events.ptr, maxEvents, -1);
>          if (-1 == n)
>              return false;
> 
>          foreach (k; 0 .. n) {
>              EventSource s = events[k].es;
>              ulong ecode = s.eventCode(events[k].event_mask); // <<<<< 
> SIGSEGV
> ```
> 
> sg0/sg1 are destroyed, so s points to wrong location.
> 
> 

Note that s likely still points at a valid memory address. However, when 
an object is destroyed, its vtable is nulled out (precisely to cause a 
segfault if you try to use an already-freed object). There is also the 
possibility the memory block has been reallocated to something else, and 
that is causing the segfault. But if the segfault is consistent, most 
likely it's the former problem.

-Steve