NAME

ck_hs_init — initialize a hash set

LIBRARY

Concurrency Kit (libck, -lck)

SYNOPSIS

#include <ck_hs.h>

typedef unsigned long
ck_hs_hash_cb_t(const void *key, unsigned long seed);

typedef bool
ck_hs_compare_cb_t(const void *c1, const void *c2);

bool
ck_hs_init(ck_hs_t *hs, unsigned int mode, ck_hs_hash_cb_t *hash_function, ck_hs_compare_cb_t *compare, struct ck_malloc *allocator, unsigned long capacity, unsigned long seed);

DESCRIPTION

The ck_hs_init() function initializes the hash set pointed to by the hs pointer.

The argument mode specifies the type of key-value pairs to be stored in the hash set as well as the expected concurrent access model. The value of mode consists of a bitfield of one of the following:

CK_HS_MODE_OBJECT: The hash set is meant to store pointers to objects. This provides a hint that only CK_MD_VMA_BITS are necessary to encode the key argument. Any unused pointer bits are leveraged for internal optimizations.
CK_HS_MODE_DIRECT: The hash set is meant to directly store key values and that all bits of the key are used to encode values.

The concurrent access model is specified by:

CK_HS_MODE_SPMC: The hash set should allow for concurrent readers in the presence of a single writer.
CK_HS_MODE_MPMC: The hash set should allow for concurrent readers in the presence of concurrent writers. This is currently unsupported.

The developer is free to specify additional workload hints. These hints are one of:

CK_HS_MODE_DELETE: The hash set is expected to have a delete-heavy workload. At the cost of approximately 13% increased memory usage, allow for stronger per-slot probe bounds to combat the effects of tombstone accumulation.

The argument hash_function is a mandatory pointer to a user-specified hash function. A user-specified hash function takes two arguments. The key argument is a pointer to a key. The seed argument is the initial seed associated with the hash set. This initial seed is specified by the user in ck_hs_init(3).

The compare argument is an optional pointer to a user-specified key comparison function. If NULL is specified in this argument, then pointer equality will be used to determine key equality. A user-specified comparison function takes two arguments representing pointers to the objects being compared for equality. It is expected to return true if the keys are of equal value and false otherwise.

The allocator argument is a pointer to a structure containing malloc and free function pointers which respectively define the memory allocation and destruction functions to be used by the hash set being initialized.

The argument capacity represents the initial number of keys the hash set is expected to contain. This argument is simply a hint and the underlying implementation is free to allocate more or less memory than necessary to contain the number of entries capacity specifies.

The argument seed specifies the initial seed used by the underlying hash function. The user is free to choose a value of their choice.

RETURN VALUES

Upon successful completion ck_hs_init() returns a value of true and otherwise returns a value of false to indicate an error.

ERRORS

The behavior of ck_hs_init() is undefined if hs is not a pointer to a ck_hs_t object.