Assert in debug build when memory_pool alloc/dealloc in certain order

[jwdevel]

Below is a simple test that fails for me on the debug build.
I get the error:

[foonathan::memory] Assertion failure in function allocate (.../foonathan-memory/src/detail/free_list.cpp:444): Assertion "last_dealloc_prev_ == prev" failed.

I am not sure if this is a genuine error that the debug build is detecting, or if it is an error introduced by the different behavior present in debug builds...

typedef foonathan::memory::memory_pool<> MyPool;
MyPool pool(100, 1024);
auto p1 = pool.allocate_node();
auto p2 = pool.allocate_node();
pool.deallocate_node(p1);
pool.deallocate_node(p2);

p1 = pool.allocate_node();
p2 = pool.allocate_node();  // <-- assertion happens here
pool.deallocate_node(p1);
pool.deallocate_node(p2);

[jwdevel]

Note: it passes on 'RelWithDeb', too.

[foonathan]

Thanks for catching that one! It seems this has been a bug for years, but as it only happens if you deallocate in the exact same order that you allocated (and most containers destroy in reverse order), nobody ran into it before, apparently.

I've expanded the tests as well: previously, they tested only one "random" ordering of allocations and deallocations, now they do same order and reverse order as well.