cds::container::feldman_hashset::make_traits< Options > Struct Template Reference

Metafunction converting option list to feldman_hashset::traits. More...

#include <cds/container/details/feldman_hashset_base.h>

Public Types
typedef implementation_defined	type
	Metafunction result.

Detailed Description

template<typename... Options>
struct cds::container::feldman_hashset::make_traits< Options >

Metafunction converting option list to feldman_hashset::traits.

Supported Options are:

• feldman_hashset::hash_accessor - mandatory option, hash accessor functor. It is most-important feature of FeldmanHashSet. That functor must return a reference to fixed-sized hash value of data node. The return value of that functor specifies the type of hash value.

Example:

typedef uint8_t hash_type[32]; // 256-bit hash type
struct foo {
    hash_type  hash; // 256-bit hash value
    // ... other fields
};

// Hash accessor
struct foo_hash_accessor {
    hash_type const& operator()( foo const& d ) const
    {
        return d.hash;
    }
};

• feldman_hashset::hash_size - the size of hash value in bytes. By default, the size of hash value is sizeof( hash_type ). Sometimes it is not correct, for example, for that 6-byte struct static_assert will be thrown:

  struct key_type {
      uint32_t    key1;
      uint16_t    subkey;
  };
  
  static_assert( sizeof( key_type ) == 6, "Key type size mismatch" );

  For that case you can specify hash_size explicitly.

Value 0 means sizeof( hash_type ).

• feldman_hashset::hash_splitter - a hash splitter algorithm This trait specifies hash bit-string splitter algorithm. By default, cds::algo::number_splitter is used if HashType is a number, cds::algo::split_bitstring otherwise.
• opt::allocator - item allocator Default is CDS_DEFAULT_ALLOCATOR
• opt::node_allocator - array node allocator. Allocator for array nodes. The allocator is used for creating headNode and arrayNode when the set grows. Default is CDS_DEFAULT_ALLOCATOR
• opt::compare - hash comparison functor. No default functor is provided. If the option is not specified, the opt::less is used.
• opt::less - specifies binary predicate used for hash comparison. If less and compare are not specified, memcmp() -like bit-wise hash comparator is used because the hash value is treated as fixed-sized bit-string.
• opt::back_off - back-off strategy used. If the option is not specified, the cds::backoff::Default is used.
• opt::item_counter - the type of item counting feature. The item counting is an important part of FeldmanHashSet algorithm: the empty() member function depends on correct item counting. Therefore, atomicity::empty_item_counter is not allowed as a type of the option.

Default is atomicity::item_counter. To avoid false sharing you can aldo use atomicity::cache_friendly_item_counter

• opt::memory_model - C++ memory ordering model. Can be opt::v::relaxed_ordering (relaxed memory model, the default) or opt::v::sequential_consistent (sequentially consisnent memory model).
• opt::stat - internal statistics. By default, it is disabled (feldman_hashset::empty_stat). To enable it use feldman_hashset::stat
• opt::rcu_check_deadlock - a deadlock checking policy for RCU-based FeldmanHashSet Default is opt::v::rcu_throw_deadlock

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The documentation for this struct was generated from the following file:

• cds/container/details/feldman_hashset_base.h