The kernel radar: folios, multi-generational LRU, and Rust

Posted Feb 6, 2022 3:02 UTC (Sun) by HelloWorld (guest, #56129)
In reply to: The kernel radar: folios, multi-generational LRU, and Rust by NYKevin
Parent article: The kernel radar: folios, multi-generational LRU, and Rust

> 2. In C++, std::bad_alloc is thrown, which is like the managed case except that stack unwinding will cause destructors to run (in the managed case, finalizers *might* run, but there is no guarantee of when they get called). If any of those destructors tries to allocate any memory, for any reason, it might cause a second std::bad_alloc to get thrown, and if a destructor throws an exception while another exception is already pending, the runtime gives up and calls std::terminate. Therefore, if you want to handle fallible allocations, every destructor in your entire program must be in on the joke.

Well, most destructors don't require allocation but do free up some memory. This means that when a bad_alloc is thrown, there's a pretty good chance that by the time you reach a destructor that allocates, some memory has already been freed by a destructor that ran before, and so your allocation may very well succeed. There are cases where it's better to try to recover from an allocation failure and sometimes fail than to not try at all.

Also, you might be able to allocate whatever memory you need to run the destructor in the constructor, thus avoiding the need to allocate in the destructor.