Set tube->ev_listen to NULL to prevent double unregister in winsock code path #774
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On windows when using threaded mode (i.e. `ub_ctx_async(ctx, 1)`) tube_remove_bg_listen gets called twice: once when the thread does its own cleanup, then again in `tube_delete()`. Because `ev_listen` doesn't get cleared, however, we end we calling ub_winsock_unregister_wsaevent with a freed pointer. This doesn't always manifest because, apparently, for various compilers and settings that memory *might* be overwritten in which case the additional check for ev->magic will prevent anything actually happening, but in my case under mingw32 that doesn't happen and we end up eventually crashing. This fixes the crash by properly NULLing the pointer so that the second ub_winsock_unregister_wsaevent(...) becomes a no-op.
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On windows when using threaded mode (i.e.
ub_ctx_async(ctx, 1))tube_remove_bg_listengets called twice during aub_ctx_delete: once when the thread does its own cleanup, then again intube_delete(). Becauseev_listendoesn't get cleared, however, we end we callingub_winsock_unregister_wsaevent()with a freed pointer on the second call.This doesn't always manifest because, apparently, for various compilers and settings that memory might be overwritten in which case the additional check for ev->magic will prevent anything actually happening, but in my case under mingw32 that doesn't happen and we end up crashing (but frustratingly does get changed under gdb, which made this rather annoying to track down).
This fixes the crash by properly NULLing the pointer so that the second
ub_winsock_unregister_wsaevent(...)becomes a no-op.(Setting it to null also matches what the non-winsock version of the code does).