doubt about C API resource release

[979357361]

Hi, good day,

As far as I know, all C API with a xx_create (call new and return a pointer) has a destroy func to free the memory, normally they should appear in pairs, but I have found some exception, I would to know if they are bugs or on purpose.

For example, rocksdb_slicetransform_create_fixed_prefix returns a point points to a wrapper struct, if I call set func rocksdb_options_set_prefix_extractor to set it to rocksdb_option, inside the set func it directly call reset(), then if I destroy the rocksdb_options and prefix itself, core dump happened. What will happen to rocksdb_filterpolicy_create_bloom_full is similar to that of prefix, they both return pointer to wapper struct and call reset() directly inside set func.

void rocksdb_options_set_prefix_extractor(
    rocksdb_options_t* opt, rocksdb_slicetransform_t* prefix_extractor) {
  opt->rep.prefix_extractor.reset(prefix_extractor);
}

Another situation is inside set func, a new struct will be built and reset to option, such as what happens in rocksdb_options_set_block_based_table_factory. I also found there is situation where bare pointer is directly assigned, rocksdb_options_set_comparator for example, and shared_ptr directly assigned, rocksdb_block_based_options_set_block_cache.

The destroy function cannot be called in some cases make me feel confused. Are there any clear guidelines for resource release?

BTW, I have found that if I finish read, after closed the db by rocksdb_close, destroyed the rocksdb_option and table open and block cache, memory used by block cache are not all freed (only part of), is that rational? What should I do to let the block cache memory all freed and returned to sys?