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/js/lib/Socket.IO-node/support/expresso/deps/jscoverage/js/jsdhash.h

http://github.com/onedayitwillmake/RealtimeMultiplayerNodeJs
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  1/* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
  2/* ***** BEGIN LICENSE BLOCK *****
  3 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
  4 *
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 37 * ***** END LICENSE BLOCK ***** */
 38
 39#ifndef jsdhash_h___
 40#define jsdhash_h___
 41/*
 42 * Double hashing, a la Knuth 6.
 43 */
 44#include "jstypes.h"
 45
 46JS_BEGIN_EXTERN_C
 47
 48#if defined(__GNUC__) && defined(__i386__) && (__GNUC__ >= 3) && !defined(XP_OS2)
 49#define JS_DHASH_FASTCALL __attribute__ ((regparm (3),stdcall))
 50#elif defined(XP_WIN)
 51#define JS_DHASH_FASTCALL __fastcall
 52#else
 53#define JS_DHASH_FASTCALL
 54#endif
 55
 56#ifdef DEBUG_XXXbrendan
 57#define JS_DHASHMETER 1
 58#endif
 59
 60/* Table size limit, do not equal or exceed (see min&maxAlphaFrac, below). */
 61#undef JS_DHASH_SIZE_LIMIT
 62#define JS_DHASH_SIZE_LIMIT     JS_BIT(24)
 63
 64/* Minimum table size, or gross entry count (net is at most .75 loaded). */
 65#ifndef JS_DHASH_MIN_SIZE
 66#define JS_DHASH_MIN_SIZE 16
 67#elif (JS_DHASH_MIN_SIZE & (JS_DHASH_MIN_SIZE - 1)) != 0
 68#error "JS_DHASH_MIN_SIZE must be a power of two!"
 69#endif
 70
 71/*
 72 * Multiplicative hash uses an unsigned 32 bit integer and the golden ratio,
 73 * expressed as a fixed-point 32-bit fraction.
 74 */
 75#define JS_DHASH_BITS           32
 76#define JS_DHASH_GOLDEN_RATIO   0x9E3779B9U
 77
 78/* Primitive and forward-struct typedefs. */
 79typedef uint32                  JSDHashNumber;
 80typedef struct JSDHashEntryHdr  JSDHashEntryHdr;
 81typedef struct JSDHashEntryStub JSDHashEntryStub;
 82typedef struct JSDHashTable     JSDHashTable;
 83typedef struct JSDHashTableOps  JSDHashTableOps;
 84
 85/*
 86 * Table entry header structure.
 87 *
 88 * In order to allow in-line allocation of key and value, we do not declare
 89 * either here.  Instead, the API uses const void *key as a formal parameter.
 90 * The key need not be stored in the entry; it may be part of the value, but
 91 * need not be stored at all.
 92 *
 93 * Callback types are defined below and grouped into the JSDHashTableOps
 94 * structure, for single static initialization per hash table sub-type.
 95 *
 96 * Each hash table sub-type should nest the JSDHashEntryHdr structure at the
 97 * front of its particular entry type.  The keyHash member contains the result
 98 * of multiplying the hash code returned from the hashKey callback (see below)
 99 * by JS_DHASH_GOLDEN_RATIO, then constraining the result to avoid the magic 0
100 * and 1 values.  The stored keyHash value is table size invariant, and it is
101 * maintained automatically by JS_DHashTableOperate -- users should never set
102 * it, and its only uses should be via the entry macros below.
103 *
104 * The JS_DHASH_ENTRY_IS_LIVE macro tests whether entry is neither free nor
105 * removed.  An entry may be either busy or free; if busy, it may be live or
106 * removed.  Consumers of this API should not access members of entries that
107 * are not live.
108 *
109 * However, use JS_DHASH_ENTRY_IS_BUSY for faster liveness testing of entries
110 * returned by JS_DHashTableOperate, as JS_DHashTableOperate never returns a
111 * non-live, busy (i.e., removed) entry pointer to its caller.  See below for
112 * more details on JS_DHashTableOperate's calling rules.
113 */
114struct JSDHashEntryHdr {
115    JSDHashNumber       keyHash;        /* every entry must begin like this */
116};
117
118#define JS_DHASH_ENTRY_IS_FREE(entry)   ((entry)->keyHash == 0)
119#define JS_DHASH_ENTRY_IS_BUSY(entry)   (!JS_DHASH_ENTRY_IS_FREE(entry))
120#define JS_DHASH_ENTRY_IS_LIVE(entry)   ((entry)->keyHash >= 2)
121
122/*
123 * A JSDHashTable is currently 8 words (without the JS_DHASHMETER overhead)
124 * on most architectures, and may be allocated on the stack or within another
125 * structure or class (see below for the Init and Finish functions to use).
126 *
127 * To decide whether to use double hashing vs. chaining, we need to develop a
128 * trade-off relation, as follows:
129 *
130 * Let alpha be the load factor, esize the entry size in words, count the
131 * entry count, and pow2 the power-of-two table size in entries.
132 *
133 *   (JSDHashTable overhead)    > (JSHashTable overhead)
134 *   (unused table entry space) > (malloc and .next overhead per entry) +
135 *                                (buckets overhead)
136 *   (1 - alpha) * esize * pow2 > 2 * count + pow2
137 *
138 * Notice that alpha is by definition (count / pow2):
139 *
140 *   (1 - alpha) * esize * pow2 > 2 * alpha * pow2 + pow2
141 *   (1 - alpha) * esize        > 2 * alpha + 1
142 *
143 *   esize > (1 + 2 * alpha) / (1 - alpha)
144 *
145 * This assumes both tables must keep keyHash, key, and value for each entry,
146 * where key and value point to separately allocated strings or structures.
147 * If key and value can be combined into one pointer, then the trade-off is:
148 *
149 *   esize > (1 + 3 * alpha) / (1 - alpha)
150 *
151 * If the entry value can be a subtype of JSDHashEntryHdr, rather than a type
152 * that must be allocated separately and referenced by an entry.value pointer
153 * member, and provided key's allocation can be fused with its entry's, then
154 * k (the words wasted per entry with chaining) is 4.
155 *
156 * To see these curves, feed gnuplot input like so:
157 *
158 *   gnuplot> f(x,k) = (1 + k * x) / (1 - x)
159 *   gnuplot> plot [0:.75] f(x,2), f(x,3), f(x,4)
160 *
161 * For k of 2 and a well-loaded table (alpha > .5), esize must be more than 4
162 * words for chaining to be more space-efficient than double hashing.
163 *
164 * Solving for alpha helps us decide when to shrink an underloaded table:
165 *
166 *   esize                     > (1 + k * alpha) / (1 - alpha)
167 *   esize - alpha * esize     > 1 + k * alpha
168 *   esize - 1                 > (k + esize) * alpha
169 *   (esize - 1) / (k + esize) > alpha
170 *
171 *   alpha < (esize - 1) / (esize + k)
172 *
173 * Therefore double hashing should keep alpha >= (esize - 1) / (esize + k),
174 * assuming esize is not too large (in which case, chaining should probably be
175 * used for any alpha).  For esize=2 and k=3, we want alpha >= .2; for esize=3
176 * and k=2, we want alpha >= .4.  For k=4, esize could be 6, and alpha >= .5
177 * would still obtain.  See the JS_DHASH_MIN_ALPHA macro further below.
178 *
179 * The current implementation uses a configurable lower bound on alpha, which
180 * defaults to .25, when deciding to shrink the table (while still respecting
181 * JS_DHASH_MIN_SIZE).
182 *
183 * Note a qualitative difference between chaining and double hashing: under
184 * chaining, entry addresses are stable across table shrinks and grows.  With
185 * double hashing, you can't safely hold an entry pointer and use it after an
186 * ADD or REMOVE operation, unless you sample table->generation before adding
187 * or removing, and compare the sample after, dereferencing the entry pointer
188 * only if table->generation has not changed.
189 *
190 * The moral of this story: there is no one-size-fits-all hash table scheme,
191 * but for small table entry size, and assuming entry address stability is not
192 * required, double hashing wins.
193 */
194struct JSDHashTable {
195    const JSDHashTableOps *ops;         /* virtual operations, see below */
196    void                *data;          /* ops- and instance-specific data */
197    int16               hashShift;      /* multiplicative hash shift */
198    uint8               maxAlphaFrac;   /* 8-bit fixed point max alpha */
199    uint8               minAlphaFrac;   /* 8-bit fixed point min alpha */
200    uint32              entrySize;      /* number of bytes in an entry */
201    uint32              entryCount;     /* number of entries in table */
202    uint32              removedCount;   /* removed entry sentinels in table */
203    uint32              generation;     /* entry storage generation number */
204    char                *entryStore;    /* entry storage */
205#ifdef JS_DHASHMETER
206    struct JSDHashStats {
207        uint32          searches;       /* total number of table searches */
208        uint32          steps;          /* hash chain links traversed */
209        uint32          hits;           /* searches that found key */
210        uint32          misses;         /* searches that didn't find key */
211        uint32          lookups;        /* number of JS_DHASH_LOOKUPs */
212        uint32          addMisses;      /* adds that miss, and do work */
213        uint32          addOverRemoved; /* adds that recycled a removed entry */
214        uint32          addHits;        /* adds that hit an existing entry */
215        uint32          addFailures;    /* out-of-memory during add growth */
216        uint32          removeHits;     /* removes that hit, and do work */
217        uint32          removeMisses;   /* useless removes that miss */
218        uint32          removeFrees;    /* removes that freed entry directly */
219        uint32          removeEnums;    /* removes done by Enumerate */
220        uint32          grows;          /* table expansions */
221        uint32          shrinks;        /* table contractions */
222        uint32          compresses;     /* table compressions */
223        uint32          enumShrinks;    /* contractions after Enumerate */
224    } stats;
225#endif
226};
227
228/*
229 * Size in entries (gross, not net of free and removed sentinels) for table.
230 * We store hashShift rather than sizeLog2 to optimize the collision-free case
231 * in SearchTable.
232 */
233#define JS_DHASH_TABLE_SIZE(table)  JS_BIT(JS_DHASH_BITS - (table)->hashShift)
234
235/*
236 * Table space at entryStore is allocated and freed using these callbacks.
237 * The allocator should return null on error only (not if called with nbytes
238 * equal to 0; but note that jsdhash.c code will never call with 0 nbytes).
239 */
240typedef void *
241(* JSDHashAllocTable)(JSDHashTable *table, uint32 nbytes);
242
243typedef void
244(* JSDHashFreeTable) (JSDHashTable *table, void *ptr);
245
246/*
247 * Compute the hash code for a given key to be looked up, added, or removed
248 * from table.  A hash code may have any JSDHashNumber value.
249 */
250typedef JSDHashNumber
251(* JSDHashHashKey)   (JSDHashTable *table, const void *key);
252
253/*
254 * Compare the key identifying entry in table with the provided key parameter.
255 * Return JS_TRUE if keys match, JS_FALSE otherwise.
256 */
257typedef JSBool
258(* JSDHashMatchEntry)(JSDHashTable *table, const JSDHashEntryHdr *entry,
259                      const void *key);
260
261/*
262 * Copy the data starting at from to the new entry storage at to.  Do not add
263 * reference counts for any strong references in the entry, however, as this
264 * is a "move" operation: the old entry storage at from will be freed without
265 * any reference-decrementing callback shortly.
266 */
267typedef void
268(* JSDHashMoveEntry)(JSDHashTable *table, const JSDHashEntryHdr *from,
269                     JSDHashEntryHdr *to);
270
271/*
272 * Clear the entry and drop any strong references it holds.  This callback is
273 * invoked during a JS_DHASH_REMOVE operation (see below for operation codes),
274 * but only if the given key is found in the table.
275 */
276typedef void
277(* JSDHashClearEntry)(JSDHashTable *table, JSDHashEntryHdr *entry);
278
279/*
280 * Called when a table (whether allocated dynamically by itself, or nested in
281 * a larger structure, or allocated on the stack) is finished.  This callback
282 * allows table->ops-specific code to finalize table->data.
283 */
284typedef void
285(* JSDHashFinalize)  (JSDHashTable *table);
286
287/*
288 * Initialize a new entry, apart from keyHash.  This function is called when
289 * JS_DHashTableOperate's JS_DHASH_ADD case finds no existing entry for the
290 * given key, and must add a new one.  At that point, entry->keyHash is not
291 * set yet, to avoid claiming the last free entry in a severely overloaded
292 * table.
293 */
294typedef JSBool
295(* JSDHashInitEntry)(JSDHashTable *table, JSDHashEntryHdr *entry,
296                     const void *key);
297
298/*
299 * Finally, the "vtable" structure for JSDHashTable.  The first eight hooks
300 * must be provided by implementations; they're called unconditionally by the
301 * generic jsdhash.c code.  Hooks after these may be null.
302 *
303 * Summary of allocation-related hook usage with C++ placement new emphasis:
304 *  allocTable          Allocate raw bytes with malloc, no ctors run.
305 *  freeTable           Free raw bytes with free, no dtors run.
306 *  initEntry           Call placement new using default key-based ctor.
307 *                      Return JS_TRUE on success, JS_FALSE on error.
308 *  moveEntry           Call placement new using copy ctor, run dtor on old
309 *                      entry storage.
310 *  clearEntry          Run dtor on entry.
311 *  finalize            Stub unless table->data was initialized and needs to
312 *                      be finalized.
313 *
314 * Note the reason why initEntry is optional: the default hooks (stubs) clear
315 * entry storage:  On successful JS_DHashTableOperate(tbl, key, JS_DHASH_ADD),
316 * the returned entry pointer addresses an entry struct whose keyHash member
317 * has been set non-zero, but all other entry members are still clear (null).
318 * JS_DHASH_ADD callers can test such members to see whether the entry was
319 * newly created by the JS_DHASH_ADD call that just succeeded.  If placement
320 * new or similar initialization is required, define an initEntry hook.  Of
321 * course, the clearEntry hook must zero or null appropriately.
322 *
323 * XXX assumes 0 is null for pointer types.
324 */
325struct JSDHashTableOps {
326    /* Mandatory hooks.  All implementations must provide these. */
327    JSDHashAllocTable   allocTable;
328    JSDHashFreeTable    freeTable;
329    JSDHashHashKey      hashKey;
330    JSDHashMatchEntry   matchEntry;
331    JSDHashMoveEntry    moveEntry;
332    JSDHashClearEntry   clearEntry;
333    JSDHashFinalize     finalize;
334
335    /* Optional hooks start here.  If null, these are not called. */
336    JSDHashInitEntry    initEntry;
337};
338
339/*
340 * Default implementations for the above ops.
341 */
342extern JS_PUBLIC_API(void *)
343JS_DHashAllocTable(JSDHashTable *table, uint32 nbytes);
344
345extern JS_PUBLIC_API(void)
346JS_DHashFreeTable(JSDHashTable *table, void *ptr);
347
348extern JS_PUBLIC_API(JSDHashNumber)
349JS_DHashStringKey(JSDHashTable *table, const void *key);
350
351/* A minimal entry contains a keyHash header and a void key pointer. */
352struct JSDHashEntryStub {
353    JSDHashEntryHdr hdr;
354    const void      *key;
355};
356
357extern JS_PUBLIC_API(JSDHashNumber)
358JS_DHashVoidPtrKeyStub(JSDHashTable *table, const void *key);
359
360extern JS_PUBLIC_API(JSBool)
361JS_DHashMatchEntryStub(JSDHashTable *table,
362                       const JSDHashEntryHdr *entry,
363                       const void *key);
364
365extern JS_PUBLIC_API(JSBool)
366JS_DHashMatchStringKey(JSDHashTable *table,
367                       const JSDHashEntryHdr *entry,
368                       const void *key);
369
370extern JS_PUBLIC_API(void)
371JS_DHashMoveEntryStub(JSDHashTable *table,
372                      const JSDHashEntryHdr *from,
373                      JSDHashEntryHdr *to);
374
375extern JS_PUBLIC_API(void)
376JS_DHashClearEntryStub(JSDHashTable *table, JSDHashEntryHdr *entry);
377
378extern JS_PUBLIC_API(void)
379JS_DHashFreeStringKey(JSDHashTable *table, JSDHashEntryHdr *entry);
380
381extern JS_PUBLIC_API(void)
382JS_DHashFinalizeStub(JSDHashTable *table);
383
384/*
385 * If you use JSDHashEntryStub or a subclass of it as your entry struct, and
386 * if your entries move via memcpy and clear via memset(0), you can use these
387 * stub operations.
388 */
389extern JS_PUBLIC_API(const JSDHashTableOps *)
390JS_DHashGetStubOps(void);
391
392/*
393 * Dynamically allocate a new JSDHashTable using malloc, initialize it using
394 * JS_DHashTableInit, and return its address.  Return null on malloc failure.
395 * Note that the entry storage at table->entryStore will be allocated using
396 * the ops->allocTable callback.
397 */
398extern JS_PUBLIC_API(JSDHashTable *)
399JS_NewDHashTable(const JSDHashTableOps *ops, void *data, uint32 entrySize,
400                 uint32 capacity);
401
402/*
403 * Finalize table's data, free its entry storage (via table->ops->freeTable),
404 * and return the memory starting at table to the malloc heap.
405 */
406extern JS_PUBLIC_API(void)
407JS_DHashTableDestroy(JSDHashTable *table);
408
409/*
410 * Initialize table with ops, data, entrySize, and capacity.  Capacity is a
411 * guess for the smallest table size at which the table will usually be less
412 * than 75% loaded (the table will grow or shrink as needed; capacity serves
413 * only to avoid inevitable early growth from JS_DHASH_MIN_SIZE).
414 */
415extern JS_PUBLIC_API(JSBool)
416JS_DHashTableInit(JSDHashTable *table, const JSDHashTableOps *ops, void *data,
417                  uint32 entrySize, uint32 capacity);
418
419/*
420 * Set maximum and minimum alpha for table.  The defaults are 0.75 and .25.
421 * maxAlpha must be in [0.5, 0.9375] for the default JS_DHASH_MIN_SIZE; or if
422 * MinSize=JS_DHASH_MIN_SIZE <= 256, in [0.5, (float)(MinSize-1)/MinSize]; or
423 * else in [0.5, 255.0/256].  minAlpha must be in [0, maxAlpha / 2), so that
424 * we don't shrink on the very next remove after growing a table upon adding
425 * an entry that brings entryCount past maxAlpha * tableSize.
426 */
427extern JS_PUBLIC_API(void)
428JS_DHashTableSetAlphaBounds(JSDHashTable *table,
429                            float maxAlpha,
430                            float minAlpha);
431
432/*
433 * Call this macro with k, the number of pointer-sized words wasted per entry
434 * under chaining, to compute the minimum alpha at which double hashing still
435 * beats chaining.
436 */
437#define JS_DHASH_MIN_ALPHA(table, k)                                          \
438    ((float)((table)->entrySize / sizeof(void *) - 1)                         \
439     / ((table)->entrySize / sizeof(void *) + (k)))
440
441/*
442 * Default max/min alpha, and macros to compute the value for the |capacity|
443 * parameter to JS_NewDHashTable and JS_DHashTableInit, given default or any
444 * max alpha, such that adding entryCount entries right after initializing the
445 * table will not require a reallocation (so JS_DHASH_ADD can't fail for those
446 * JS_DHashTableOperate calls).
447 *
448 * NB: JS_DHASH_CAP is a helper macro meant for use only in JS_DHASH_CAPACITY.
449 * Don't use it directly!
450 */
451#define JS_DHASH_DEFAULT_MAX_ALPHA 0.75
452#define JS_DHASH_DEFAULT_MIN_ALPHA 0.25
453
454#define JS_DHASH_CAP(entryCount, maxAlpha)                                    \
455    ((uint32)((double)(entryCount) / (maxAlpha)))
456
457#define JS_DHASH_CAPACITY(entryCount, maxAlpha)                               \
458    (JS_DHASH_CAP(entryCount, maxAlpha) +                                     \
459     (((JS_DHASH_CAP(entryCount, maxAlpha) * (uint8)(0x100 * (maxAlpha)))     \
460       >> 8) < (entryCount)))
461
462#define JS_DHASH_DEFAULT_CAPACITY(entryCount)                                 \
463    JS_DHASH_CAPACITY(entryCount, JS_DHASH_DEFAULT_MAX_ALPHA)
464
465/*
466 * Finalize table's data, free its entry storage using table->ops->freeTable,
467 * and leave its members unchanged from their last live values (which leaves
468 * pointers dangling).  If you want to burn cycles clearing table, it's up to
469 * your code to call memset.
470 */
471extern JS_PUBLIC_API(void)
472JS_DHashTableFinish(JSDHashTable *table);
473
474/*
475 * To consolidate keyHash computation and table grow/shrink code, we use a
476 * single entry point for lookup, add, and remove operations.  The operation
477 * codes are declared here, along with codes returned by JSDHashEnumerator
478 * functions, which control JS_DHashTableEnumerate's behavior.
479 */
480typedef enum JSDHashOperator {
481    JS_DHASH_LOOKUP = 0,        /* lookup entry */
482    JS_DHASH_ADD = 1,           /* add entry */
483    JS_DHASH_REMOVE = 2,        /* remove entry, or enumerator says remove */
484    JS_DHASH_NEXT = 0,          /* enumerator says continue */
485    JS_DHASH_STOP = 1           /* enumerator says stop */
486} JSDHashOperator;
487
488/*
489 * To lookup a key in table, call:
490 *
491 *  entry = JS_DHashTableOperate(table, key, JS_DHASH_LOOKUP);
492 *
493 * If JS_DHASH_ENTRY_IS_BUSY(entry) is true, key was found and it identifies
494 * entry.  If JS_DHASH_ENTRY_IS_FREE(entry) is true, key was not found.
495 *
496 * To add an entry identified by key to table, call:
497 *
498 *  entry = JS_DHashTableOperate(table, key, JS_DHASH_ADD);
499 *
500 * If entry is null upon return, then either the table is severely overloaded,
501 * and memory can't be allocated for entry storage via table->ops->allocTable;
502 * Or if table->ops->initEntry is non-null, the table->ops->initEntry op may
503 * have returned false.
504 *
505 * Otherwise, entry->keyHash has been set so that JS_DHASH_ENTRY_IS_BUSY(entry)
506 * is true, and it is up to the caller to initialize the key and value parts
507 * of the entry sub-type, if they have not been set already (i.e. if entry was
508 * not already in the table, and if the optional initEntry hook was not used).
509 *
510 * To remove an entry identified by key from table, call:
511 *
512 *  (void) JS_DHashTableOperate(table, key, JS_DHASH_REMOVE);
513 *
514 * If key's entry is found, it is cleared (via table->ops->clearEntry) and
515 * the entry is marked so that JS_DHASH_ENTRY_IS_FREE(entry).  This operation
516 * returns null unconditionally; you should ignore its return value.
517 */
518extern JS_PUBLIC_API(JSDHashEntryHdr *) JS_DHASH_FASTCALL
519JS_DHashTableOperate(JSDHashTable *table, const void *key, JSDHashOperator op);
520
521/*
522 * Remove an entry already accessed via LOOKUP or ADD.
523 *
524 * NB: this is a "raw" or low-level routine, intended to be used only where
525 * the inefficiency of a full JS_DHashTableOperate (which rehashes in order
526 * to find the entry given its key) is not tolerable.  This function does not
527 * shrink the table if it is underloaded.  It does not update stats #ifdef
528 * JS_DHASHMETER, either.
529 */
530extern JS_PUBLIC_API(void)
531JS_DHashTableRawRemove(JSDHashTable *table, JSDHashEntryHdr *entry);
532
533/*
534 * Enumerate entries in table using etor:
535 *
536 *   count = JS_DHashTableEnumerate(table, etor, arg);
537 *
538 * JS_DHashTableEnumerate calls etor like so:
539 *
540 *   op = etor(table, entry, number, arg);
541 *
542 * where number is a zero-based ordinal assigned to live entries according to
543 * their order in table->entryStore.
544 *
545 * The return value, op, is treated as a set of flags.  If op is JS_DHASH_NEXT,
546 * then continue enumerating.  If op contains JS_DHASH_REMOVE, then clear (via
547 * table->ops->clearEntry) and free entry.  Then we check whether op contains
548 * JS_DHASH_STOP; if so, stop enumerating and return the number of live entries
549 * that were enumerated so far.  Return the total number of live entries when
550 * enumeration completes normally.
551 *
552 * If etor calls JS_DHashTableOperate on table with op != JS_DHASH_LOOKUP, it
553 * must return JS_DHASH_STOP; otherwise undefined behavior results.
554 *
555 * If any enumerator returns JS_DHASH_REMOVE, table->entryStore may be shrunk
556 * or compressed after enumeration, but before JS_DHashTableEnumerate returns.
557 * Such an enumerator therefore can't safely set aside entry pointers, but an
558 * enumerator that never returns JS_DHASH_REMOVE can set pointers to entries
559 * aside, e.g., to avoid copying live entries into an array of the entry type.
560 * Copying entry pointers is cheaper, and safe so long as the caller of such a
561 * "stable" Enumerate doesn't use the set-aside pointers after any call either
562 * to PL_DHashTableOperate, or to an "unstable" form of Enumerate, which might
563 * grow or shrink entryStore.
564 *
565 * If your enumerator wants to remove certain entries, but set aside pointers
566 * to other entries that it retains, it can use JS_DHashTableRawRemove on the
567 * entries to be removed, returning JS_DHASH_NEXT to skip them.  Likewise, if
568 * you want to remove entries, but for some reason you do not want entryStore
569 * to be shrunk or compressed, you can call JS_DHashTableRawRemove safely on
570 * the entry being enumerated, rather than returning JS_DHASH_REMOVE.
571 */
572typedef JSDHashOperator
573(* JSDHashEnumerator)(JSDHashTable *table, JSDHashEntryHdr *hdr, uint32 number,
574                      void *arg);
575
576extern JS_PUBLIC_API(uint32)
577JS_DHashTableEnumerate(JSDHashTable *table, JSDHashEnumerator etor, void *arg);
578
579#ifdef JS_DHASHMETER
580#include <stdio.h>
581
582extern JS_PUBLIC_API(void)
583JS_DHashTableDumpMeter(JSDHashTable *table, JSDHashEnumerator dump, FILE *fp);
584#endif
585
586JS_END_EXTERN_C
587
588#endif /* jsdhash_h___ */