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 *
5 * The contents of this file are subject to the Mozilla Public License Version
6 * 1.1 (the "License"); you may not use this file except in compliance with
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11 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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14 *
15 * The Original Code is Mozilla JavaScript code.
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17 * The Initial Developer of the Original Code is
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19 * Portions created by the Initial Developer are Copyright (C) 1999-2001
20 * the Initial Developer. All Rights Reserved.
21 *
22 * Contributor(s):
23 * Brendan Eich <brendan@mozilla.org> (Original Author)
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37 * ***** END LICENSE BLOCK ***** */
39 #ifndef jsdhash_h___
40 #define jsdhash_h___
41 /*
42 * Double hashing, a la Knuth 6.
43 */
44 #include "jstypes.h"
46 JS_BEGIN_EXTERN_C
48 #if defined(__GNUC__) && defined(__i386__) && (__GNUC__ >= 3) && !defined(XP_OS2)
49 #define JS_DHASH_FASTCALL __attribute__ ((regparm (3),stdcall))
50 #else
51 #define JS_DHASH_FASTCALL
52 #endif
54 #ifdef DEBUG_XXXbrendan
55 #define JS_DHASHMETER 1
56 #endif
58 /* Table size limit, do not equal or exceed (see min&maxAlphaFrac, below). */
59 #undef JS_DHASH_SIZE_LIMIT
60 #define JS_DHASH_SIZE_LIMIT JS_BIT(24)
62 /* Minimum table size, or gross entry count (net is at most .75 loaded). */
63 #ifndef JS_DHASH_MIN_SIZE
64 #define JS_DHASH_MIN_SIZE 16
65 #elif (JS_DHASH_MIN_SIZE & (JS_DHASH_MIN_SIZE - 1)) != 0
66 #error "JS_DHASH_MIN_SIZE must be a power of two!"
67 #endif
69 /*
70 * Multiplicative hash uses an unsigned 32 bit integer and the golden ratio,
71 * expressed as a fixed-point 32-bit fraction.
72 */
73 #define JS_DHASH_BITS 32
74 #define JS_DHASH_GOLDEN_RATIO 0x9E3779B9U
76 /* Primitive and forward-struct typedefs. */
77 typedef uint32 JSDHashNumber;
78 typedef struct JSDHashEntryHdr JSDHashEntryHdr;
79 typedef struct JSDHashEntryStub JSDHashEntryStub;
80 typedef struct JSDHashTable JSDHashTable;
81 typedef struct JSDHashTableOps JSDHashTableOps;
83 /*
84 * Table entry header structure.
85 *
86 * In order to allow in-line allocation of key and value, we do not declare
87 * either here. Instead, the API uses const void *key as a formal parameter,
88 * and asks each entry for its key when necessary via a getKey callback, used
89 * when growing or shrinking the table. Other callback types are defined
90 * below and grouped into the JSDHashTableOps structure, for single static
91 * initialization per hash table sub-type.
92 *
93 * Each hash table sub-type should nest the JSDHashEntryHdr structure at the
94 * front of its particular entry type. The keyHash member contains the result
95 * of multiplying the hash code returned from the hashKey callback (see below)
96 * by JS_DHASH_GOLDEN_RATIO, then constraining the result to avoid the magic 0
97 * and 1 values. The stored keyHash value is table size invariant, and it is
98 * maintained automatically by JS_DHashTableOperate -- users should never set
99 * it, and its only uses should be via the entry macros below.
100 *
101 * The JS_DHASH_ENTRY_IS_LIVE macro tests whether entry is neither free nor
102 * removed. An entry may be either busy or free; if busy, it may be live or
103 * removed. Consumers of this API should not access members of entries that
104 * are not live.
105 *
106 * However, use JS_DHASH_ENTRY_IS_BUSY for faster liveness testing of entries
107 * returned by JS_DHashTableOperate, as JS_DHashTableOperate never returns a
108 * non-live, busy (i.e., removed) entry pointer to its caller. See below for
109 * more details on JS_DHashTableOperate's calling rules.
110 */
111 struct JSDHashEntryHdr {
112 JSDHashNumber keyHash; /* every entry must begin like this */
113 };
115 #define JS_DHASH_ENTRY_IS_FREE(entry) ((entry)->keyHash == 0)
116 #define JS_DHASH_ENTRY_IS_BUSY(entry) (!JS_DHASH_ENTRY_IS_FREE(entry))
117 #define JS_DHASH_ENTRY_IS_LIVE(entry) ((entry)->keyHash >= 2)
119 /*
120 * A JSDHashTable is currently 8 words (without the JS_DHASHMETER overhead)
121 * on most architectures, and may be allocated on the stack or within another
122 * structure or class (see below for the Init and Finish functions to use).
123 *
124 * To decide whether to use double hashing vs. chaining, we need to develop a
125 * trade-off relation, as follows:
126 *
127 * Let alpha be the load factor, esize the entry size in words, count the
128 * entry count, and pow2 the power-of-two table size in entries.
129 *
130 * (JSDHashTable overhead) > (JSHashTable overhead)
131 * (unused table entry space) > (malloc and .next overhead per entry) +
132 * (buckets overhead)
133 * (1 - alpha) * esize * pow2 > 2 * count + pow2
134 *
135 * Notice that alpha is by definition (count / pow2):
136 *
137 * (1 - alpha) * esize * pow2 > 2 * alpha * pow2 + pow2
138 * (1 - alpha) * esize > 2 * alpha + 1
139 *
140 * esize > (1 + 2 * alpha) / (1 - alpha)
141 *
142 * This assumes both tables must keep keyHash, key, and value for each entry,
143 * where key and value point to separately allocated strings or structures.
144 * If key and value can be combined into one pointer, then the trade-off is:
145 *
146 * esize > (1 + 3 * alpha) / (1 - alpha)
147 *
148 * If the entry value can be a subtype of JSDHashEntryHdr, rather than a type
149 * that must be allocated separately and referenced by an entry.value pointer
150 * member, and provided key's allocation can be fused with its entry's, then
151 * k (the words wasted per entry with chaining) is 4.
152 *
153 * To see these curves, feed gnuplot input like so:
154 *
155 * gnuplot> f(x,k) = (1 + k * x) / (1 - x)
156 * gnuplot> plot [0:.75] f(x,2), f(x,3), f(x,4)
157 *
158 * For k of 2 and a well-loaded table (alpha > .5), esize must be more than 4
159 * words for chaining to be more space-efficient than double hashing.
160 *
161 * Solving for alpha helps us decide when to shrink an underloaded table:
162 *
163 * esize > (1 + k * alpha) / (1 - alpha)
164 * esize - alpha * esize > 1 + k * alpha
165 * esize - 1 > (k + esize) * alpha
166 * (esize - 1) / (k + esize) > alpha
167 *
168 * alpha < (esize - 1) / (esize + k)
169 *
170 * Therefore double hashing should keep alpha >= (esize - 1) / (esize + k),
171 * assuming esize is not too large (in which case, chaining should probably be
172 * used for any alpha). For esize=2 and k=3, we want alpha >= .2; for esize=3
173 * and k=2, we want alpha >= .4. For k=4, esize could be 6, and alpha >= .5
174 * would still obtain. See the JS_DHASH_MIN_ALPHA macro further below.
175 *
176 * The current implementation uses a configurable lower bound on alpha, which
177 * defaults to .25, when deciding to shrink the table (while still respecting
178 * JS_DHASH_MIN_SIZE).
179 *
180 * Note a qualitative difference between chaining and double hashing: under
181 * chaining, entry addresses are stable across table shrinks and grows. With
182 * double hashing, you can't safely hold an entry pointer and use it after an
183 * ADD or REMOVE operation, unless you sample table->generation before adding
184 * or removing, and compare the sample after, dereferencing the entry pointer
185 * only if table->generation has not changed.
186 *
187 * The moral of this story: there is no one-size-fits-all hash table scheme,
188 * but for small table entry size, and assuming entry address stability is not
189 * required, double hashing wins.
190 */
191 struct JSDHashTable {
192 const JSDHashTableOps *ops; /* virtual operations, see below */
193 void *data; /* ops- and instance-specific data */
194 int16 hashShift; /* multiplicative hash shift */
195 uint8 maxAlphaFrac; /* 8-bit fixed point max alpha */
196 uint8 minAlphaFrac; /* 8-bit fixed point min alpha */
197 uint32 entrySize; /* number of bytes in an entry */
198 uint32 entryCount; /* number of entries in table */
199 uint32 removedCount; /* removed entry sentinels in table */
200 uint32 generation; /* entry storage generation number */
201 char *entryStore; /* entry storage */
202 #ifdef JS_DHASHMETER
203 struct JSDHashStats {
204 uint32 searches; /* total number of table searches */
205 uint32 steps; /* hash chain links traversed */
206 uint32 hits; /* searches that found key */
207 uint32 misses; /* searches that didn't find key */
208 uint32 lookups; /* number of JS_DHASH_LOOKUPs */
209 uint32 addMisses; /* adds that miss, and do work */
210 uint32 addOverRemoved; /* adds that recycled a removed entry */
211 uint32 addHits; /* adds that hit an existing entry */
212 uint32 addFailures; /* out-of-memory during add growth */
213 uint32 removeHits; /* removes that hit, and do work */
214 uint32 removeMisses; /* useless removes that miss */
215 uint32 removeFrees; /* removes that freed entry directly */
216 uint32 removeEnums; /* removes done by Enumerate */
217 uint32 grows; /* table expansions */
218 uint32 shrinks; /* table contractions */
219 uint32 compresses; /* table compressions */
220 uint32 enumShrinks; /* contractions after Enumerate */
221 } stats;
222 #endif
223 };
225 /*
226 * Size in entries (gross, not net of free and removed sentinels) for table.
227 * We store hashShift rather than sizeLog2 to optimize the collision-free case
228 * in SearchTable.
229 */
230 #define JS_DHASH_TABLE_SIZE(table) JS_BIT(JS_DHASH_BITS - (table)->hashShift)
232 /*
233 * Table space at entryStore is allocated and freed using these callbacks.
234 * The allocator should return null on error only (not if called with nbytes
235 * equal to 0; but note that jsdhash.c code will never call with 0 nbytes).
236 */
237 typedef void *
238 (* JS_DLL_CALLBACK JSDHashAllocTable)(JSDHashTable *table, uint32 nbytes);
240 typedef void
241 (* JS_DLL_CALLBACK JSDHashFreeTable) (JSDHashTable *table, void *ptr);
243 /*
244 * When a table grows or shrinks, each entry is queried for its key using this
245 * callback. NB: in that event, entry is not in table any longer; it's in the
246 * old entryStore vector, which is due to be freed once all entries have been
247 * moved via moveEntry callbacks.
248 */
249 typedef const void *
250 (* JS_DLL_CALLBACK JSDHashGetKey) (JSDHashTable *table,
251 JSDHashEntryHdr *entry);
253 /*
254 * Compute the hash code for a given key to be looked up, added, or removed
255 * from table. A hash code may have any JSDHashNumber value.
256 */
257 typedef JSDHashNumber
258 (* JS_DLL_CALLBACK JSDHashHashKey) (JSDHashTable *table, const void *key);
260 /*
261 * Compare the key identifying entry in table with the provided key parameter.
262 * Return JS_TRUE if keys match, JS_FALSE otherwise.
263 */
264 typedef JSBool
265 (* JS_DLL_CALLBACK JSDHashMatchEntry)(JSDHashTable *table,
266 const JSDHashEntryHdr *entry,
267 const void *key);
269 /*
270 * Copy the data starting at from to the new entry storage at to. Do not add
271 * reference counts for any strong references in the entry, however, as this
272 * is a "move" operation: the old entry storage at from will be freed without
273 * any reference-decrementing callback shortly.
274 */
275 typedef void
276 (* JS_DLL_CALLBACK JSDHashMoveEntry)(JSDHashTable *table,
277 const JSDHashEntryHdr *from,
278 JSDHashEntryHdr *to);
280 /*
281 * Clear the entry and drop any strong references it holds. This callback is
282 * invoked during a JS_DHASH_REMOVE operation (see below for operation codes),
283 * but only if the given key is found in the table.
284 */
285 typedef void
286 (* JS_DLL_CALLBACK JSDHashClearEntry)(JSDHashTable *table,
287 JSDHashEntryHdr *entry);
289 /*
290 * Called when a table (whether allocated dynamically by itself, or nested in
291 * a larger structure, or allocated on the stack) is finished. This callback
292 * allows table->ops-specific code to finalize table->data.
293 */
294 typedef void
295 (* JS_DLL_CALLBACK JSDHashFinalize) (JSDHashTable *table);
297 /*
298 * Initialize a new entry, apart from keyHash. This function is called when
299 * JS_DHashTableOperate's JS_DHASH_ADD case finds no existing entry for the
300 * given key, and must add a new one. At that point, entry->keyHash is not
301 * set yet, to avoid claiming the last free entry in a severely overloaded
302 * table.
303 */
304 typedef JSBool
305 (* JS_DLL_CALLBACK JSDHashInitEntry)(JSDHashTable *table,
306 JSDHashEntryHdr *entry,
307 const void *key);
309 /*
310 * Finally, the "vtable" structure for JSDHashTable. The first eight hooks
311 * must be provided by implementations; they're called unconditionally by the
312 * generic jsdhash.c code. Hooks after these may be null.
313 *
314 * Summary of allocation-related hook usage with C++ placement new emphasis:
315 * allocTable Allocate raw bytes with malloc, no ctors run.
316 * freeTable Free raw bytes with free, no dtors run.
317 * initEntry Call placement new using default key-based ctor.
318 * Return JS_TRUE on success, JS_FALSE on error.
319 * moveEntry Call placement new using copy ctor, run dtor on old
320 * entry storage.
321 * clearEntry Run dtor on entry.
322 * finalize Stub unless table->data was initialized and needs to
323 * be finalized.
324 *
325 * Note the reason why initEntry is optional: the default hooks (stubs) clear
326 * entry storage: On successful JS_DHashTableOperate(tbl, key, JS_DHASH_ADD),
327 * the returned entry pointer addresses an entry struct whose keyHash member
328 * has been set non-zero, but all other entry members are still clear (null).
329 * JS_DHASH_ADD callers can test such members to see whether the entry was
330 * newly created by the JS_DHASH_ADD call that just succeeded. If placement
331 * new or similar initialization is required, define an initEntry hook. Of
332 * course, the clearEntry hook must zero or null appropriately.
333 *
334 * XXX assumes 0 is null for pointer types.
335 */
336 struct JSDHashTableOps {
337 /* Mandatory hooks. All implementations must provide these. */
338 JSDHashAllocTable allocTable;
339 JSDHashFreeTable freeTable;
340 JSDHashGetKey getKey;
341 JSDHashHashKey hashKey;
342 JSDHashMatchEntry matchEntry;
343 JSDHashMoveEntry moveEntry;
344 JSDHashClearEntry clearEntry;
345 JSDHashFinalize finalize;
347 /* Optional hooks start here. If null, these are not called. */
348 JSDHashInitEntry initEntry;
349 };
351 /*
352 * Default implementations for the above ops.
353 */
354 extern JS_PUBLIC_API(void *)
355 JS_DHashAllocTable(JSDHashTable *table, uint32 nbytes);
357 extern JS_PUBLIC_API(void)
358 JS_DHashFreeTable(JSDHashTable *table, void *ptr);
360 extern JS_PUBLIC_API(JSDHashNumber)
361 JS_DHashStringKey(JSDHashTable *table, const void *key);
363 /* A minimal entry contains a keyHash header and a void key pointer. */
364 struct JSDHashEntryStub {
365 JSDHashEntryHdr hdr;
366 const void *key;
367 };
369 extern JS_PUBLIC_API(const void *)
370 JS_DHashGetKeyStub(JSDHashTable *table, JSDHashEntryHdr *entry);
372 extern JS_PUBLIC_API(JSDHashNumber)
373 JS_DHashVoidPtrKeyStub(JSDHashTable *table, const void *key);
375 extern JS_PUBLIC_API(JSBool)
376 JS_DHashMatchEntryStub(JSDHashTable *table,
377 const JSDHashEntryHdr *entry,
378 const void *key);
380 extern JS_PUBLIC_API(JSBool)
381 JS_DHashMatchStringKey(JSDHashTable *table,
382 const JSDHashEntryHdr *entry,
383 const void *key);
385 extern JS_PUBLIC_API(void)
386 JS_DHashMoveEntryStub(JSDHashTable *table,
387 const JSDHashEntryHdr *from,
388 JSDHashEntryHdr *to);
390 extern JS_PUBLIC_API(void)
391 JS_DHashClearEntryStub(JSDHashTable *table, JSDHashEntryHdr *entry);
393 extern JS_PUBLIC_API(void)
394 JS_DHashFreeStringKey(JSDHashTable *table, JSDHashEntryHdr *entry);
396 extern JS_PUBLIC_API(void)
397 JS_DHashFinalizeStub(JSDHashTable *table);
399 /*
400 * If you use JSDHashEntryStub or a subclass of it as your entry struct, and
401 * if your entries move via memcpy and clear via memset(0), you can use these
402 * stub operations.
403 */
404 extern JS_PUBLIC_API(const JSDHashTableOps *)
405 JS_DHashGetStubOps(void);
407 /*
408 * Dynamically allocate a new JSDHashTable using malloc, initialize it using
409 * JS_DHashTableInit, and return its address. Return null on malloc failure.
410 * Note that the entry storage at table->entryStore will be allocated using
411 * the ops->allocTable callback.
412 */
413 extern JS_PUBLIC_API(JSDHashTable *)
414 JS_NewDHashTable(const JSDHashTableOps *ops, void *data, uint32 entrySize,
415 uint32 capacity);
417 /*
418 * Finalize table's data, free its entry storage (via table->ops->freeTable),
419 * and return the memory starting at table to the malloc heap.
420 */
421 extern JS_PUBLIC_API(void)
422 JS_DHashTableDestroy(JSDHashTable *table);
424 /*
425 * Initialize table with ops, data, entrySize, and capacity. Capacity is a
426 * guess for the smallest table size at which the table will usually be less
427 * than 75% loaded (the table will grow or shrink as needed; capacity serves
428 * only to avoid inevitable early growth from JS_DHASH_MIN_SIZE).
429 */
430 extern JS_PUBLIC_API(JSBool)
431 JS_DHashTableInit(JSDHashTable *table, const JSDHashTableOps *ops, void *data,
432 uint32 entrySize, uint32 capacity);
434 /*
435 * Set maximum and minimum alpha for table. The defaults are 0.75 and .25.
436 * maxAlpha must be in [0.5, 0.9375] for the default JS_DHASH_MIN_SIZE; or if
437 * MinSize=JS_DHASH_MIN_SIZE <= 256, in [0.5, (float)(MinSize-1)/MinSize]; or
438 * else in [0.5, 255.0/256]. minAlpha must be in [0, maxAlpha / 2), so that
439 * we don't shrink on the very next remove after growing a table upon adding
440 * an entry that brings entryCount past maxAlpha * tableSize.
441 */
442 extern JS_PUBLIC_API(void)
443 JS_DHashTableSetAlphaBounds(JSDHashTable *table,
444 float maxAlpha,
445 float minAlpha);
447 /*
448 * Call this macro with k, the number of pointer-sized words wasted per entry
449 * under chaining, to compute the minimum alpha at which double hashing still
450 * beats chaining.
451 */
452 #define JS_DHASH_MIN_ALPHA(table, k) \
453 ((float)((table)->entrySize / sizeof(void *) - 1) \
454 / ((table)->entrySize / sizeof(void *) + (k)))
456 /*
457 * Finalize table's data, free its entry storage using table->ops->freeTable,
458 * and leave its members unchanged from their last live values (which leaves
459 * pointers dangling). If you want to burn cycles clearing table, it's up to
460 * your code to call memset.
461 */
462 extern JS_PUBLIC_API(void)
463 JS_DHashTableFinish(JSDHashTable *table);
465 /*
466 * To consolidate keyHash computation and table grow/shrink code, we use a
467 * single entry point for lookup, add, and remove operations. The operation
468 * codes are declared here, along with codes returned by JSDHashEnumerator
469 * functions, which control JS_DHashTableEnumerate's behavior.
470 */
471 typedef enum JSDHashOperator {
472 JS_DHASH_LOOKUP = 0, /* lookup entry */
473 JS_DHASH_ADD = 1, /* add entry */
474 JS_DHASH_REMOVE = 2, /* remove entry, or enumerator says remove */
475 JS_DHASH_NEXT = 0, /* enumerator says continue */
476 JS_DHASH_STOP = 1 /* enumerator says stop */
477 } JSDHashOperator;
479 /*
480 * To lookup a key in table, call:
481 *
482 * entry = JS_DHashTableOperate(table, key, JS_DHASH_LOOKUP);
483 *
484 * If JS_DHASH_ENTRY_IS_BUSY(entry) is true, key was found and it identifies
485 * entry. If JS_DHASH_ENTRY_IS_FREE(entry) is true, key was not found.
486 *
487 * To add an entry identified by key to table, call:
488 *
489 * entry = JS_DHashTableOperate(table, key, JS_DHASH_ADD);
490 *
491 * If entry is null upon return, then either the table is severely overloaded,
492 * and memory can't be allocated for entry storage via table->ops->allocTable;
493 * Or if table->ops->initEntry is non-null, the table->ops->initEntry op may
494 * have returned false.
495 *
496 * Otherwise, entry->keyHash has been set so that JS_DHASH_ENTRY_IS_BUSY(entry)
497 * is true, and it is up to the caller to initialize the key and value parts
498 * of the entry sub-type, if they have not been set already (i.e. if entry was
499 * not already in the table, and if the optional initEntry hook was not used).
500 *
501 * To remove an entry identified by key from table, call:
502 *
503 * (void) JS_DHashTableOperate(table, key, JS_DHASH_REMOVE);
504 *
505 * If key's entry is found, it is cleared (via table->ops->clearEntry) and
506 * the entry is marked so that JS_DHASH_ENTRY_IS_FREE(entry). This operation
507 * returns null unconditionally; you should ignore its return value.
508 */
509 extern JS_PUBLIC_API(JSDHashEntryHdr *) JS_DHASH_FASTCALL
510 JS_DHashTableOperate(JSDHashTable *table, const void *key, JSDHashOperator op);
512 /*
513 * Remove an entry already accessed via LOOKUP or ADD.
514 *
515 * NB: this is a "raw" or low-level routine, intended to be used only where
516 * the inefficiency of a full JS_DHashTableOperate (which rehashes in order
517 * to find the entry given its key) is not tolerable. This function does not
518 * shrink the table if it is underloaded. It does not update stats #ifdef
519 * JS_DHASHMETER, either.
520 */
521 extern JS_PUBLIC_API(void)
522 JS_DHashTableRawRemove(JSDHashTable *table, JSDHashEntryHdr *entry);
524 /*
525 * Enumerate entries in table using etor:
526 *
527 * count = JS_DHashTableEnumerate(table, etor, arg);
528 *
529 * JS_DHashTableEnumerate calls etor like so:
530 *
531 * op = etor(table, entry, number, arg);
532 *
533 * where number is a zero-based ordinal assigned to live entries according to
534 * their order in table->entryStore.
535 *
536 * The return value, op, is treated as a set of flags. If op is JS_DHASH_NEXT,
537 * then continue enumerating. If op contains JS_DHASH_REMOVE, then clear (via
538 * table->ops->clearEntry) and free entry. Then we check whether op contains
539 * JS_DHASH_STOP; if so, stop enumerating and return the number of live entries
540 * that were enumerated so far. Return the total number of live entries when
541 * enumeration completes normally.
542 *
543 * If etor calls JS_DHashTableOperate on table with op != JS_DHASH_LOOKUP, it
544 * must return JS_DHASH_STOP; otherwise undefined behavior results.
545 *
546 * If any enumerator returns JS_DHASH_REMOVE, table->entryStore may be shrunk
547 * or compressed after enumeration, but before JS_DHashTableEnumerate returns.
548 * Such an enumerator therefore can't safely set aside entry pointers, but an
549 * enumerator that never returns JS_DHASH_REMOVE can set pointers to entries
550 * aside, e.g., to avoid copying live entries into an array of the entry type.
551 * Copying entry pointers is cheaper, and safe so long as the caller of such a
552 * "stable" Enumerate doesn't use the set-aside pointers after any call either
553 * to PL_DHashTableOperate, or to an "unstable" form of Enumerate, which might
554 * grow or shrink entryStore.
555 *
556 * If your enumerator wants to remove certain entries, but set aside pointers
557 * to other entries that it retains, it can use JS_DHashTableRawRemove on the
558 * entries to be removed, returning JS_DHASH_NEXT to skip them. Likewise, if
559 * you want to remove entries, but for some reason you do not want entryStore
560 * to be shrunk or compressed, you can call JS_DHashTableRawRemove safely on
561 * the entry being enumerated, rather than returning JS_DHASH_REMOVE.
562 */
563 typedef JSDHashOperator
564 (* JS_DLL_CALLBACK JSDHashEnumerator)(JSDHashTable *table, JSDHashEntryHdr *hdr,
565 uint32 number, void *arg);
567 extern JS_PUBLIC_API(uint32)
568 JS_DHashTableEnumerate(JSDHashTable *table, JSDHashEnumerator etor, void *arg);
570 #ifdef JS_DHASHMETER
571 #include <stdio.h>
573 extern JS_PUBLIC_API(void)
574 JS_DHashTableDumpMeter(JSDHashTable *table, JSDHashEnumerator dump, FILE *fp);
575 #endif
577 JS_END_EXTERN_C
579 #endif /* jsdhash_h___ */