Limitations

Character arrays have a stack-size limit, this is system-dependent, but typically 1-2 MiB. You can make custom CharStructs with character arrays that store a lot of data, but never more than stack size.

In order to alleviate this, the intended solution in HCL is to utilize boost shared memory stack allocation. See example:

typedef boost::interprocess::allocator<char, boost::interprocess::managed_mapped_file::segment_manager> CharAllocator;
typedef bip::basic_string<char, std::char_traits<char>, CharAllocator> MappedUnitString;
hcl::unordered_map<struct KeyType, std::string, std::hash<KeyType>, CharAllocator, MappedUnitString> *hcl_string_client;

However, boost shared memory allocators also have limitations. The limitation is nearly 128 MiB, you can push to 127.9 MiB, but not all the way up to 128 (more detail at issue 22). We recommend not going over 64 MiB for boost shared memory strings, and also note that performance with this allocation is far more variable than stack allocation.