dshash.h

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/*-------------------------------------------------------------------------
 *
 * dshash.h
 *    Concurrent hash tables backed by dynamic shared memory areas.
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/include/lib/dshash.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef DSHASH_H
#define DSHASH_H
 
#include "utils/dsa.h"
 
/* The opaque type representing a hash table. */
struct dshash_table;
typedef struct dshash_table dshash_table;
 
/* A handle for a dshash_table which can be shared with other processes. */
typedef dsa_pointer dshash_table_handle;
 
/* Sentinel value to use for invalid dshash_table handles. */
#define DSHASH_HANDLE_INVALID ((dshash_table_handle) InvalidDsaPointer)
 
/* The type for hash values. */
typedef uint32 dshash_hash;
 
/* A function type for comparing keys. */
typedef int (*dshash_compare_function) (const void *a, const void *b,
                                        size_t size, void *arg);
 
/* A function type for computing hash values for keys. */
typedef dshash_hash (*dshash_hash_function) (const void *v, size_t size,
                                             void *arg);
 
/* A function type for copying keys. */
typedef void (*dshash_copy_function) (void *dest, const void *src, size_t size,
                                      void *arg);
 
/*
 * The set of parameters needed to create or attach to a hash table.  The
 * tranche_id member does not need to be initialized when attaching to an
 * existing hash table.
 *
 * Compare, hash, and copy functions must be supplied even when attaching,
 * because we can't safely share function pointers between backends in general.
 * The user data pointer supplied to the create and attach functions will be
 * passed to these functions.
 */
typedef struct dshash_parameters
{
    size_t      key_size;       /* Size of the key (initial bytes of entry) */
    size_t      entry_size;     /* Total size of entry */
    dshash_compare_function compare_function;   /* Compare function */
    dshash_hash_function hash_function; /* Hash function */
    dshash_copy_function copy_function; /* Copy function */
    int         tranche_id;     /* The tranche ID to use for locks */
} dshash_parameters;
 
/* Forward declaration of private types for use only by dshash.c. */
struct dshash_table_item;
typedef struct dshash_table_item dshash_table_item;
 
/*
 * Sequential scan state. The detail is exposed to let users know the storage
 * size but it should be considered as an opaque type by callers.
 */
typedef struct dshash_seq_status
{
    dshash_table *hash_table;   /* dshash table working on */
    int         curbucket;      /* bucket number we are at */
    int         nbuckets;       /* total number of buckets in the dshash */
    dshash_table_item *curitem; /* item we are currently at */
    dsa_pointer pnextitem;      /* dsa-pointer to the next item */
    int         curpartition;   /* partition number we are at */
    bool        exclusive;      /* locking mode */
} dshash_seq_status;
 
/* Creating, sharing and destroying from hash tables. */
extern dshash_table *dshash_create(dsa_area *area,
                                   const dshash_parameters *params,
                                   void *arg);
extern dshash_table *dshash_attach(dsa_area *area,
                                   const dshash_parameters *params,
                                   dshash_table_handle handle,
                                   void *arg);
extern void dshash_detach(dshash_table *hash_table);
extern dshash_table_handle dshash_get_hash_table_handle(dshash_table *hash_table);
extern void dshash_destroy(dshash_table *hash_table);
 
/* Finding, creating, deleting entries. */
extern void *dshash_find(dshash_table *hash_table,
                         const void *key, bool exclusive);
extern void *dshash_find_or_insert(dshash_table *hash_table,
                                   const void *key, bool *found);
extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
/* seq scan support */
extern void dshash_seq_init(dshash_seq_status *status, dshash_table *hash_table,
                            bool exclusive);
extern void *dshash_seq_next(dshash_seq_status *status);
extern void dshash_seq_term(dshash_seq_status *status);
extern void dshash_delete_current(dshash_seq_status *status);
 
/*
 * Convenience hash, compare, and copy functions wrapping memcmp, tag_hash, and
 * memcpy.
 */
extern int  dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
extern void dshash_memcpy(void *dest, const void *src, size_t size, void *arg);
 
/*
 * Convenience hash, compare, and copy functions wrapping strcmp, string_hash,
 * and strcpy.
 */
extern int  dshash_strcmp(const void *a, const void *b, size_t size, void *arg);
extern dshash_hash dshash_strhash(const void *v, size_t size, void *arg);
extern void dshash_strcpy(void *dest, const void *src, size_t size, void *arg);
 
/* Debugging support. */
extern void dshash_dump(dshash_table *hash_table);
 
#endif                          /* DSHASH_H */