1 /*------------------------------------------------------------------------- 2 * 3 * dshash.h 4 * Concurrent hash tables backed by dynamic shared memory areas. 5 * 6 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group 7 * Portions Copyright (c) 1994, Regents of the University of California 8 * 9 * IDENTIFICATION 10 * src/include/lib/dshash.h 11 * 12 *------------------------------------------------------------------------- 13 */ 14 #ifndef DSHASH_H 15 #define DSHASH_H 16 17 #include "utils/dsa.h" 18 19 /* The opaque type representing a hash table. */ 20 struct dshash_table; 21 typedef struct dshash_table dshash_table; 22 23 /* A handle for a dshash_table which can be shared with other processes. */ 24 typedef dsa_pointer dshash_table_handle; 25 26 /* The type for hash values. */ 27 typedef uint32 dshash_hash; 28 29 /* A function type for comparing keys. */ 30 typedef int (*dshash_compare_function) (const void *a, const void *b, 31 size_t size, void *arg); 32 33 /* A function type for computing hash values for keys. */ 34 typedef dshash_hash (*dshash_hash_function) (const void *v, size_t size, 35 void *arg); 36 37 /* 38 * The set of parameters needed to create or attach to a hash table. The 39 * members tranche_id and tranche_name do not need to be initialized when 40 * attaching to an existing hash table. 41 * 42 * Compare and hash functions must be supplied even when attaching, because we 43 * can't safely share function pointers between backends in general. Either 44 * the arg variants or the non-arg variants should be supplied; the other 45 * function pointers should be NULL. If the arg variants are supplied then the 46 * user data pointer supplied to the create and attach functions will be 47 * passed to the hash and compare functions. 48 */ 49 typedef struct dshash_parameters 50 { 51 size_t key_size; /* Size of the key (initial bytes of entry) */ 52 size_t entry_size; /* Total size of entry */ 53 dshash_compare_function compare_function; /* Compare function */ 54 dshash_hash_function hash_function; /* Hash function */ 55 int tranche_id; /* The tranche ID to use for locks */ 56 } dshash_parameters; 57 58 /* Forward declaration of private types for use only by dshash.c. */ 59 struct dshash_table_item; 60 typedef struct dshash_table_item dshash_table_item; 61 62 /* Creating, sharing and destroying from hash tables. */ 63 extern dshash_table *dshash_create(dsa_area *area, 64 const dshash_parameters *params, 65 void *arg); 66 extern dshash_table *dshash_attach(dsa_area *area, 67 const dshash_parameters *params, 68 dshash_table_handle handle, 69 void *arg); 70 extern void dshash_detach(dshash_table *hash_table); 71 extern dshash_table_handle dshash_get_hash_table_handle(dshash_table *hash_table); 72 extern void dshash_destroy(dshash_table *hash_table); 73 74 /* Finding, creating, deleting entries. */ 75 extern void *dshash_find(dshash_table *hash_table, 76 const void *key, bool exclusive); 77 extern void *dshash_find_or_insert(dshash_table *hash_table, 78 const void *key, bool *found); 79 extern bool dshash_delete_key(dshash_table *hash_table, const void *key); 80 extern void dshash_delete_entry(dshash_table *hash_table, void *entry); 81 extern void dshash_release_lock(dshash_table *hash_table, void *entry); 82 83 /* Convenience hash and compare functions wrapping memcmp and tag_hash. */ 84 extern int dshash_memcmp(const void *a, const void *b, size_t size, void *arg); 85 extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg); 86 87 /* Debugging support. */ 88 extern void dshash_dump(dshash_table *hash_table); 89 90 #endif /* DSHASH_H */ 91