hsearch.h

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/*-------------------------------------------------------------------------
 *
 * hsearch.h
 *    exported definitions for utils/hash/dynahash.c; see notes therein
 *
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/utils/hsearch.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef HSEARCH_H
#define HSEARCH_H
 
 
/*
 * Hash functions must have this signature.
 */
typedef uint32 (*HashValueFunc) (const void *key, Size keysize);
 
/*
 * Key comparison functions must have this signature.  Comparison functions
 * return zero for match, nonzero for no match.  (The comparison function
 * definition is designed to allow memcmp() and strncmp() to be used directly
 * as key comparison functions.)
 */
typedef int (*HashCompareFunc) (const void *key1, const void *key2,
                                Size keysize);
 
/*
 * Key copying functions must have this signature.  The return value is not
 * used.  (The definition is set up to allow memcpy() and strlcpy() to be
 * used directly.)
 */
typedef void *(*HashCopyFunc) (void *dest, const void *src, Size keysize);
 
/*
 * Space allocation function for a hashtable --- designed to match malloc().
 * Note: there is no free function API; can't destroy a hashtable unless you
 * use the default allocator.
 */
typedef void *(*HashAllocFunc) (Size request);
 
/*
 * HASHELEMENT is the private part of a hashtable entry.  The caller's data
 * follows the HASHELEMENT structure (on a MAXALIGN'd boundary).  The hash key
 * is expected to be at the start of the caller's hash entry data structure.
 */
typedef struct HASHELEMENT
{
    struct HASHELEMENT *link;   /* link to next entry in same bucket */
    uint32      hashvalue;      /* hash function result for this entry */
} HASHELEMENT;
 
/* Hash table header struct is an opaque type known only within dynahash.c */
typedef struct HASHHDR HASHHDR;
 
/* Hash table control struct is an opaque type known only within dynahash.c */
typedef struct HTAB HTAB;
 
/* Parameter data structure for hash_create */
/* Only those fields indicated by hash_flags need be set */
typedef struct HASHCTL
{
    /* Used if HASH_PARTITION flag is set: */
    long        num_partitions; /* # partitions (must be power of 2) */
    /* Used if HASH_SEGMENT flag is set: */
    long        ssize;          /* segment size */
    /* Used if HASH_DIRSIZE flag is set: */
    long        dsize;          /* (initial) directory size */
    long        max_dsize;      /* limit to dsize if dir size is limited */
    /* Used if HASH_ELEM flag is set (which is now required): */
    Size        keysize;        /* hash key length in bytes */
    Size        entrysize;      /* total user element size in bytes */
    /* Used if HASH_FUNCTION flag is set: */
    HashValueFunc hash;         /* hash function */
    /* Used if HASH_COMPARE flag is set: */
    HashCompareFunc match;      /* key comparison function */
    /* Used if HASH_KEYCOPY flag is set: */
    HashCopyFunc keycopy;       /* key copying function */
    /* Used if HASH_ALLOC flag is set: */
    HashAllocFunc alloc;        /* memory allocator */
    /* Used if HASH_CONTEXT flag is set: */
    MemoryContext hcxt;         /* memory context to use for allocations */
    /* Used if HASH_SHARED_MEM flag is set: */
    HASHHDR    *hctl;           /* location of header in shared mem */
} HASHCTL;
 
/* Flag bits for hash_create; most indicate which parameters are supplied */
#define HASH_PARTITION  0x0001  /* Hashtable is used w/partitioned locking */
#define HASH_SEGMENT    0x0002  /* Set segment size */
#define HASH_DIRSIZE    0x0004  /* Set directory size (initial and max) */
#define HASH_ELEM       0x0008  /* Set keysize and entrysize (now required!) */
#define HASH_STRINGS    0x0010  /* Select support functions for string keys */
#define HASH_BLOBS      0x0020  /* Select support functions for binary keys */
#define HASH_FUNCTION   0x0040  /* Set user defined hash function */
#define HASH_COMPARE    0x0080  /* Set user defined comparison function */
#define HASH_KEYCOPY    0x0100  /* Set user defined key-copying function */
#define HASH_ALLOC      0x0200  /* Set memory allocator */
#define HASH_CONTEXT    0x0400  /* Set memory allocation context */
#define HASH_SHARED_MEM 0x0800  /* Hashtable is in shared memory */
#define HASH_ATTACH     0x1000  /* Do not initialize hctl */
#define HASH_FIXED_SIZE 0x2000  /* Initial size is a hard limit */
 
/* max_dsize value to indicate expansible directory */
#define NO_MAX_DSIZE            (-1)
 
/* hash_search operations */
typedef enum
{
    HASH_FIND,
    HASH_ENTER,
    HASH_REMOVE,
    HASH_ENTER_NULL,
} HASHACTION;
 
/* hash_seq status (should be considered an opaque type by callers) */
typedef struct
{
    HTAB       *hashp;
    uint32      curBucket;      /* index of current bucket */
    HASHELEMENT *curEntry;      /* current entry in bucket */
    bool        hasHashvalue;   /* true if hashvalue was provided */
    uint32      hashvalue;      /* hashvalue to start seqscan over hash */
} HASH_SEQ_STATUS;
 
/*
 * prototypes for functions in dynahash.c
 */
extern HTAB *hash_create(const char *tabname, long nelem,
                         const HASHCTL *info, int flags);
extern void hash_destroy(HTAB *hashp);
extern void hash_stats(const char *where, HTAB *hashp);
extern void *hash_search(HTAB *hashp, const void *keyPtr, HASHACTION action,
                         bool *foundPtr);
extern uint32 get_hash_value(HTAB *hashp, const void *keyPtr);
extern void *hash_search_with_hash_value(HTAB *hashp, const void *keyPtr,
                                         uint32 hashvalue, HASHACTION action,
                                         bool *foundPtr);
extern bool hash_update_hash_key(HTAB *hashp, void *existingEntry,
                                 const void *newKeyPtr);
extern long hash_get_num_entries(HTAB *hashp);
extern void hash_seq_init(HASH_SEQ_STATUS *status, HTAB *hashp);
extern void hash_seq_init_with_hash_value(HASH_SEQ_STATUS *status,
                                          HTAB *hashp,
                                          uint32 hashvalue);
extern void *hash_seq_search(HASH_SEQ_STATUS *status);
extern void hash_seq_term(HASH_SEQ_STATUS *status);
extern void hash_freeze(HTAB *hashp);
extern Size hash_estimate_size(long num_entries, Size entrysize);
extern long hash_select_dirsize(long num_entries);
extern Size hash_get_shared_size(HASHCTL *info, int flags);
extern void AtEOXact_HashTables(bool isCommit);
extern void AtEOSubXact_HashTables(bool isCommit, int nestDepth);
 
#endif                          /* HSEARCH_H */