jsdhash.h

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typedef void
(* JS_DLL_CALLBACK JSDHashFinalize)  (JSDHashTable *table);

/*
 * Initialize a new entry, apart from keyHash.  This function is called when
 * JS_DHashTableOperate's JS_DHASH_ADD case finds no existing entry for the
 * given key, and must add a new one.  At that point, entry->keyHash is not
 * set yet, to avoid claiming the last free entry in a severely overloaded
 * table.
 */
typedef JSBool
(* JS_DLL_CALLBACK JSDHashInitEntry)(JSDHashTable *table,
                                     JSDHashEntryHdr *entry,
                                     const void *key);

/*
 * Finally, the "vtable" structure for JSDHashTable.  The first eight hooks
 * must be provided by implementations; they're called unconditionally by the
 * generic jsdhash.c code.  Hooks after these may be null.
 *
 * Summary of allocation-related hook usage with C++ placement new emphasis:
 *  allocTable          Allocate raw bytes with malloc, no ctors run.
 *  freeTable           Free raw bytes with free, no dtors run.
 *  initEntry           Call placement new using default key-based ctor.
 *                      Return JS_TRUE on success, JS_FALSE on error.
 *  moveEntry           Call placement new using copy ctor, run dtor on old
 *                      entry storage.
 *  clearEntry          Run dtor on entry.
 *  finalize            Stub unless table->data was initialized and needs to
 *                      be finalized.
 *
 * Note the reason why initEntry is optional: the default hooks (stubs) clear
 * entry storage:  On successful JS_DHashTableOperate(tbl, key, JS_DHASH_ADD),
 * the returned entry pointer addresses an entry struct whose keyHash member
 * has been set non-zero, but all other entry members are still clear (null).
 * JS_DHASH_ADD callers can test such members to see whether the entry was
 * newly created by the JS_DHASH_ADD call that just succeeded.  If placement
 * new or similar initialization is required, define an initEntry hook.  Of
 * course, the clearEntry hook must zero or null appropriately.
 *
 * XXX assumes 0 is null for pointer types.
 */
struct JSDHashTableOps {
    /* Mandatory hooks.  All implementations must provide these. */
    JSDHashAllocTable   allocTable;
    JSDHashFreeTable    freeTable;
    JSDHashGetKey       getKey;
    JSDHashHashKey      hashKey;
    JSDHashMatchEntry   matchEntry;
    JSDHashMoveEntry    moveEntry;
    JSDHashClearEntry   clearEntry;
    JSDHashFinalize     finalize;

    /* Optional hooks start here.  If null, these are not called. */
    JSDHashInitEntry    initEntry;
};

/*
 * Default implementations for the above ops.
 */
extern JS_PUBLIC_API(void *)
JS_DHashAllocTable(JSDHashTable *table, uint32 nbytes);

extern JS_PUBLIC_API(void)
JS_DHashFreeTable(JSDHashTable *table, void *ptr);

extern JS_PUBLIC_API(JSDHashNumber)
JS_DHashStringKey(JSDHashTable *table, const void *key);

/* A minimal entry contains a keyHash header and a void key pointer. */
struct JSDHashEntryStub {
    JSDHashEntryHdr hdr;
    const void      *key;
};

extern JS_PUBLIC_API(const void *)
JS_DHashGetKeyStub(JSDHashTable *table, JSDHashEntryHdr *entry);

extern JS_PUBLIC_API(JSDHashNumber)
JS_DHashVoidPtrKeyStub(JSDHashTable *table, const void *key);

extern JS_PUBLIC_API(JSBool)
JS_DHashMatchEntryStub(JSDHashTable *table,
                       const JSDHashEntryHdr *entry,
                       const void *key);

extern JS_PUBLIC_API(JSBool)
JS_DHashMatchStringKey(JSDHashTable *table,
                       const JSDHashEntryHdr *entry,
                       const void *key);

extern JS_PUBLIC_API(void)
JS_DHashMoveEntryStub(JSDHashTable *table,
                      const JSDHashEntryHdr *from,
                      JSDHashEntryHdr *to);

extern JS_PUBLIC_API(void)
JS_DHashClearEntryStub(JSDHashTable *table, JSDHashEntryHdr *entry);

extern JS_PUBLIC_API(void)
JS_DHashFreeStringKey(JSDHashTable *table, JSDHashEntryHdr *entry);

extern JS_PUBLIC_API(void)
JS_DHashFinalizeStub(JSDHashTable *table);

/*
 * If you use JSDHashEntryStub or a subclass of it as your entry struct, and
 * if your entries move via memcpy and clear via memset(0), you can use these
 * stub operations.
 */
extern JS_PUBLIC_API(const JSDHashTableOps *)
JS_DHashGetStubOps(void);

/*
 * Dynamically allocate a new JSDHashTable using malloc, initialize it using
 * JS_DHashTableInit, and return its address.  Return null on malloc failure.
 * Note that the entry storage at table->entryStore will be allocated using
 * the ops->allocTable callback.
 */
extern JS_PUBLIC_API(JSDHashTable *)
JS_NewDHashTable(const JSDHashTableOps *ops, void *data, uint32 entrySize,
                 uint32 capacity);

/*
 * Finalize table's data, free its entry storage (via table->ops->freeTable),
 * and return the memory starting at table to the malloc heap.
 */
extern JS_PUBLIC_API(void)
JS_DHashTableDestroy(JSDHashTable *table);

/*
 * Initialize table with ops, data, entrySize, and capacity.  Capacity is a
 * guess for the smallest table size at which the table will usually be less
 * than 75% loaded (the table will grow or shrink as needed; capacity serves
 * only to avoid inevitable early growth from JS_DHASH_MIN_SIZE).
 */
extern JS_PUBLIC_API(JSBool)
JS_DHashTableInit(JSDHashTable *table, const JSDHashTableOps *ops, void *data,
                  uint32 entrySize, uint32 capacity);

/*
 * Set maximum and minimum alpha for table.  The defaults are 0.75 and .25.
 * maxAlpha must be in [0.5, 0.9375] for the default JS_DHASH_MIN_SIZE; or if
 * MinSize=JS_DHASH_MIN_SIZE <= 256, in [0.5, (float)(MinSize-1)/MinSize]; or
 * else in [0.5, 255.0/256].  minAlpha must be in [0, maxAlpha / 2), so that
 * we don't shrink on the very next remove after growing a table upon adding
 * an entry that brings entryCount past maxAlpha * tableSize.
 */
JS_PUBLIC_API(void)
JS_DHashTableSetAlphaBounds(JSDHashTable *table,
                            float maxAlpha,
                            float minAlpha);

/*
 * Call this macro with k, the number of pointer-sized words wasted per entry
 * under chaining, to compute the minimum alpha at which double hashing still
 * beats chaining.
 */
#define JS_DHASH_MIN_ALPHA(table, k)                                          \
    ((float)((table)->entrySize / sizeof(void *) - 1)                         \
     / ((table)->entrySize / sizeof(void *) + (k)))

/*
 * Finalize table's data, free its entry storage using table->ops->freeTable,
 * and leave its members unchanged from their last live values (which leaves
 * pointers dangling).  If you want to burn cycles clearing table, it's up to
 * your code to call memset.
 */
extern JS_PUBLIC_API(void)
JS_DHashTableFinish(JSDHashTable *table);

/*
 * To consolidate keyHash computation and table grow/shrink code, we use a
 * single entry point for lookup, add, and remove operations.  The operation
 * codes are declared here, along with codes returned by JSDHashEnumerator
 * functions, which control JS_DHashTableEnumerate's behavior.
 */
typedef enum JSDHashOperator {
    JS_DHASH_LOOKUP = 0,        /* lookup entry */
    JS_DHASH_ADD = 1,           /* add entry */
    JS_DHASH_REMOVE = 2,        /* remove entry, or enumerator says remove */
    JS_DHASH_NEXT = 0,          /* enumerator says continue */
    JS_DHASH_STOP = 1           /* enumerator says stop */
} JSDHashOperator;

/*
 * To lookup a key in table, call:
 *
 *  entry = JS_DHashTableOperate(table, key, JS_DHASH_LOOKUP);
 *
 * If JS_DHASH_ENTRY_IS_BUSY(entry) is true, key was found and it identifies
 * entry.  If JS_DHASH_ENTRY_IS_FREE(entry) is true, key was not found.
 *
 * To add an entry identified by key to table, call:
 *
 *  entry = JS_DHashTableOperate(table, key, JS_DHASH_ADD);
 *
 * If entry is null upon return, then either the table is severely overloaded,
 * and memory can't be allocated for entry storage via table->ops->allocTable;
 * Or if table->ops->initEntry is non-null, the table->ops->initEntry op may
 * have returned false.
 *
 * Otherwise, entry->keyHash has been set so that JS_DHASH_ENTRY_IS_BUSY(entry)
 * is true, and it is up to the caller to initialize the key and value parts
 * of the entry sub-type, if they have not been set already (i.e. if entry was
 * not already in the table, and if the optional initEntry hook was not used).
 *
 * To remove an entry identified by key from table, call:
 *
 *  (void) JS_DHashTableOperate(table, key, JS_DHASH_REMOVE);
 *
 * If key's entry is found, it is cleared (via table->ops->clearEntry) and
 * the entry is marked so that JS_DHASH_ENTRY_IS_FREE(entry).  This operation
 * returns null unconditionally; you should ignore its return value.
 */
extern JS_PUBLIC_API(JSDHashEntryHdr *)
JS_DHashTableOperate(JSDHashTable *table, const void *key, JSDHashOperator op);

/*
 * Remove an entry already accessed via LOOKUP or ADD.
 *
 * NB: this is a "raw" or low-level routine, intended to be used only where
 * the inefficiency of a full JS_DHashTableOperate (which rehashes in order
 * to find the entry given its key) is not tolerable.  This function does not
 * shrink the table if it is underloaded.  It does not update stats #ifdef
 * JS_DHASHMETER, either.
 */
extern JS_PUBLIC_API(void)
JS_DHashTableRawRemove(JSDHashTable *table, JSDHashEntryHdr *entry);

/*
 * Enumerate entries in table using etor:
 *
 *   count = JS_DHashTableEnumerate(table, etor, arg);
 *
 * JS_DHashTableEnumerate calls etor like so:
 *
 *   op = etor(table, entry, number, arg);
 *
 * where number is a zero-based ordinal assigned to live entries according to
 * their order in table->entryStore.
 *
 * The return value, op, is treated as a set of flags.  If op is JS_DHASH_NEXT,
 * then continue enumerating.  If op contains JS_DHASH_REMOVE, then clear (via
 * table->ops->clearEntry) and free entry.  Then we check whether op contains
 * JS_DHASH_STOP; if so, stop enumerating and return the number of live entries
 * that were enumerated so far.  Return the total number of live entries when
 * enumeration completes normally.
 *
 * If etor calls JS_DHashTableOperate on table with op != JS_DHASH_LOOKUP, it
 * must return JS_DHASH_STOP; otherwise undefined behavior results.
 *
 * If any enumerator returns JS_DHASH_REMOVE, table->entryStore may be shrunk
 * or compressed after enumeration, but before JS_DHashTableEnumerate returns.
 * Such an enumerator therefore can't safely set aside entry pointers, but an
 * enumerator that never returns JS_DHASH_REMOVE can set pointers to entries
 * aside, e.g., to avoid copying live entries into an array of the entry type.
 * Copying entry pointers is cheaper, and safe so long as the caller of such a
 * "stable" Enumerate doesn't use the set-aside pointers after any call either
 * to PL_DHashTableOperate, or to an "unstable" form of Enumerate, which might
 * grow or shrink entryStore.
 *
 * If your enumerator wants to remove certain entries, but set aside pointers
 * to other entries that it retains, it can use JS_DHashTableRawRemove on the
 * entries to be removed, returning JS_DHASH_NEXT to skip them.  Likewise, if
 * you want to remove entries, but for some reason you do not want entryStore
 * to be shrunk or compressed, you can call JS_DHashTableRawRemove safely on
 * the entry being enumerated, rather than returning JS_DHASH_REMOVE.
 */
typedef JSDHashOperator
(* JS_DLL_CALLBACK JSDHashEnumerator)(JSDHashTable *table, JSDHashEntryHdr *hdr,
                                      uint32 number, void *arg);

extern JS_PUBLIC_API(uint32)
JS_DHashTableEnumerate(JSDHashTable *table, JSDHashEnumerator etor, void *arg);

#ifdef JS_DHASHMETER
#include <stdio.h>

extern JS_PUBLIC_API(void)
JS_DHashTableDumpMeter(JSDHashTable *table, JSDHashEnumerator dump, FILE *fp);
#endif

JS_END_EXTERN_C

#endif /* jsdhash_h___ */