Bug in elementBuffer

[Frogmellon]

I get an (intermittent) crash when inserting into an empty elementBuffer that's previously been used. Repeatable (intermittent) with...

Map<int32_t, String> testMap;

for (int32_t counter = 0; counter < 20; ++counter) {
        testMap.Add(counter, "testString");
        testMap.Erase(counter);
}

Crashes when counter == 8.

I believe this goes wrong in elementBuffer::prepareInsert when index = 0, size = 0 buf->start = 16 buf->end = 16 buf->cap = 16 and then elementBuffer::moveInsertFront accesses out of bounds on this line...

new(&this->buf[this->start-1]) TYPE(std::move(this->buf[start]));

...and sometime later it all unravels.

[floooh]

Whoops interesting, thanks for the simplified test case! I'll have a look tomorrow, first thing :)

[floooh]

I should run more often with the clang Address Sanitizer, this is also triggering in the Buffer class test. I'll fix that first and then move on to the elementBuffer problem.

[floooh]

clang address sanitizer is also catching the error from your test case 100%, fixing this now...

[Frogmellon]

Thanks. I've actually found the code remarkably solid for a pretty ambitious side project.

[floooh]

Ok, the fix is in commit 2d2f9f467e14adebb7b335ca27738241c11d76bd.

• first I added missing range-check asserts to elementBuffer, so that all attempted accesses outside allocated memory should be caught now (in debug mode, the asserts are disabled in release mode)
• and then the next problem was that when adding and erasing items, the chunk of valid items would slowly crawl towards the end of the allocated memory when adding and removing items because new items were preferably added to the end, and erased items were preferably removed from the front, this should now be properly balanced (I hope)

I have added your minimal test to the Map unit test, and I also checked all tests and samples with clang address- and undefined-behaviour sanitizer (next I'll do the same for the more complex oryol-samples and my 8-bit emu).

Thanks a lot for the bug report!

[Frogmellon]

Thanks a lot for the prompt fix!