It's obviously possible to find niche cases where the standard containers are not good enough. But the remaining 9999 cases out of 10000 are more interesting.

It's obviously possible to find niche cases where the standard containers are not good enough. But the remaining 9999 cases out of 10000 are more interesting. I also had one of those, in an application that created and deleted a large number of fixed-size arrays across many threads. A naive implementation using glibc malloc ended up with a massive memory leak caused by hundreds/thousands of fragmented arenas. A thread could usually not reuse the memory it had just freed, because it was using a different arena. And because the arena was not empty, it was not possible to unmap the memory.