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1.1 root 1: /* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
2: /* ***** BEGIN LICENSE BLOCK *****
3: * Version: NPL 1.1/GPL 2.0/LGPL 2.1
4: *
5: * The contents of this file are subject to the Netscape Public License
6: * Version 1.1 (the "License"); you may not use this file except in
7: * compliance with the License. You may obtain a copy of the License at
8: * http://www.mozilla.org/NPL/
9: *
10: * Software distributed under the License is distributed on an "AS IS" basis,
11: * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
12: * for the specific language governing rights and limitations under the
13: * License.
14: *
15: * The Original Code is Mozilla JavaScript code.
16: *
17: * The Initial Developer of the Original Code is
18: * Netscape Communications Corporation.
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 <[email protected]> (Original Author)
24: *
25: * Alternatively, the contents of this file may be used under the terms of
26: * either the GNU General Public License Version 2 or later (the "GPL"), or
27: * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
28: * in which case the provisions of the GPL or the LGPL are applicable instead
29: * of those above. If you wish to allow use of your version of this file only
30: * under the terms of either the GPL or the LGPL, and not to allow others to
31: * use your version of this file under the terms of the NPL, indicate your
32: * decision by deleting the provisions above and replace them with the notice
33: * and other provisions required by the GPL or the LGPL. If you do not delete
34: * the provisions above, a recipient may use your version of this file under
35: * the terms of any one of the NPL, the GPL or the LGPL.
36: *
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:
46: JS_BEGIN_EXTERN_C
47:
48: #ifdef DEBUG_XXXbrendan
49: #define JS_DHASHMETER 1
50: #endif
51:
52: /* Table size limit, do not equal or exceed (see min&maxAlphaFrac, below). */
53: #undef JS_DHASH_SIZE_LIMIT
54: #define JS_DHASH_SIZE_LIMIT JS_BIT(24)
55:
56: /* Minimum table size, or gross entry count (net is at most .75 loaded). */
57: #ifndef JS_DHASH_MIN_SIZE
58: #define JS_DHASH_MIN_SIZE 16
59: #elif (JS_DHASH_MIN_SIZE & (JS_DHASH_MIN_SIZE - 1)) != 0
60: #error "JS_DHASH_MIN_SIZE must be a power of two!"
61: #endif
62:
63: /*
64: * Multiplicative hash uses an unsigned 32 bit integer and the golden ratio,
65: * expressed as a fixed-point 32-bit fraction.
66: */
67: #define JS_DHASH_BITS 32
68: #define JS_DHASH_GOLDEN_RATIO 0x9E3779B9U
69:
70: /* Primitive and forward-struct typedefs. */
71: typedef uint32 JSDHashNumber;
72: typedef struct JSDHashEntryHdr JSDHashEntryHdr;
73: typedef struct JSDHashEntryStub JSDHashEntryStub;
74: typedef struct JSDHashTable JSDHashTable;
75: typedef struct JSDHashTableOps JSDHashTableOps;
76:
77: /*
78: * Table entry header structure.
79: *
80: * In order to allow in-line allocation of key and value, we do not declare
81: * either here. Instead, the API uses const void *key as a formal parameter,
82: * and asks each entry for its key when necessary via a getKey callback, used
83: * when growing or shrinking the table. Other callback types are defined
84: * below and grouped into the JSDHashTableOps structure, for single static
85: * initialization per hash table sub-type.
86: *
87: * Each hash table sub-type should nest the JSDHashEntryHdr structure at the
88: * front of its particular entry type. The keyHash member contains the result
89: * of multiplying the hash code returned from the hashKey callback (see below)
90: * by JS_DHASH_GOLDEN_RATIO, then constraining the result to avoid the magic 0
91: * and 1 values. The stored keyHash value is table size invariant, and it is
92: * maintained automatically by JS_DHashTableOperate -- users should never set
93: * it, and its only uses should be via the entry macros below.
94: *
95: * The JS_DHASH_ENTRY_IS_LIVE macro tests whether entry is neither free nor
96: * removed. An entry may be either busy or free; if busy, it may be live or
97: * removed. Consumers of this API should not access members of entries that
98: * are not live.
99: *
100: * However, use JS_DHASH_ENTRY_IS_BUSY for faster liveness testing of entries
101: * returned by JS_DHashTableOperate, as JS_DHashTableOperate never returns a
102: * non-live, busy (i.e., removed) entry pointer to its caller. See below for
103: * more details on JS_DHashTableOperate's calling rules.
104: */
105: struct JSDHashEntryHdr {
106: JSDHashNumber keyHash; /* every entry must begin like this */
107: };
108:
109: #define JS_DHASH_ENTRY_IS_FREE(entry) ((entry)->keyHash == 0)
110: #define JS_DHASH_ENTRY_IS_BUSY(entry) (!JS_DHASH_ENTRY_IS_FREE(entry))
111: #define JS_DHASH_ENTRY_IS_LIVE(entry) ((entry)->keyHash >= 2)
112:
113: /*
114: * A JSDHashTable is currently 8 words (without the JS_DHASHMETER overhead)
115: * on most architectures, and may be allocated on the stack or within another
116: * structure or class (see below for the Init and Finish functions to use).
117: *
118: * To decide whether to use double hashing vs. chaining, we need to develop a
119: * trade-off relation, as follows:
120: *
121: * Let alpha be the load factor, esize the entry size in words, count the
122: * entry count, and pow2 the power-of-two table size in entries.
123: *
124: * (JSDHashTable overhead) > (JSHashTable overhead)
125: * (unused table entry space) > (malloc and .next overhead per entry) +
126: * (buckets overhead)
127: * (1 - alpha) * esize * pow2 > 2 * count + pow2
128: *
129: * Notice that alpha is by definition (count / pow2):
130: *
131: * (1 - alpha) * esize * pow2 > 2 * alpha * pow2 + pow2
132: * (1 - alpha) * esize > 2 * alpha + 1
133: *
134: * esize > (1 + 2 * alpha) / (1 - alpha)
135: *
136: * This assumes both tables must keep keyHash, key, and value for each entry,
137: * where key and value point to separately allocated strings or structures.
138: * If key and value can be combined into one pointer, then the trade-off is:
139: *
140: * esize > (1 + 3 * alpha) / (1 - alpha)
141: *
142: * If the entry value can be a subtype of JSDHashEntryHdr, rather than a type
143: * that must be allocated separately and referenced by an entry.value pointer
144: * member, and provided key's allocation can be fused with its entry's, then
145: * k (the words wasted per entry with chaining) is 4.
146: *
147: * To see these curves, feed gnuplot input like so:
148: *
149: * gnuplot> f(x,k) = (1 + k * x) / (1 - x)
150: * gnuplot> plot [0:.75] f(x,2), f(x,3), f(x,4)
151: *
152: * For k of 2 and a well-loaded table (alpha > .5), esize must be more than 4
153: * words for chaining to be more space-efficient than double hashing.
154: *
155: * Solving for alpha helps us decide when to shrink an underloaded table:
156: *
157: * esize > (1 + k * alpha) / (1 - alpha)
158: * esize - alpha * esize > 1 + k * alpha
159: * esize - 1 > (k + esize) * alpha
160: * (esize - 1) / (k + esize) > alpha
161: *
162: * alpha < (esize - 1) / (esize + k)
163: *
164: * Therefore double hashing should keep alpha >= (esize - 1) / (esize + k),
165: * assuming esize is not too large (in which case, chaining should probably be
166: * used for any alpha). For esize=2 and k=3, we want alpha >= .2; for esize=3
167: * and k=2, we want alpha >= .4. For k=4, esize could be 6, and alpha >= .5
168: * would still obtain. See the JS_DHASH_MIN_ALPHA macro further below.
169: *
170: * The current implementation uses a configurable lower bound on alpha, which
171: * defaults to .25, when deciding to shrink the table (while still respecting
172: * JS_DHASH_MIN_SIZE).
173: *
174: * Note a qualitative difference between chaining and double hashing: under
175: * chaining, entry addresses are stable across table shrinks and grows. With
176: * double hashing, you can't safely hold an entry pointer and use it after an
177: * ADD or REMOVE operation, unless you sample table->generation before adding
178: * or removing, and compare the sample after, dereferencing the entry pointer
179: * only if table->generation has not changed.
180: *
181: * The moral of this story: there is no one-size-fits-all hash table scheme,
182: * but for small table entry size, and assuming entry address stability is not
183: * required, double hashing wins.
184: */
185: struct JSDHashTable {
186: const JSDHashTableOps *ops; /* virtual operations, see below */
187: void *data; /* ops- and instance-specific data */
188: int16 hashShift; /* multiplicative hash shift */
189: uint8 maxAlphaFrac; /* 8-bit fixed point max alpha */
190: uint8 minAlphaFrac; /* 8-bit fixed point min alpha */
191: uint32 entrySize; /* number of bytes in an entry */
192: uint32 entryCount; /* number of entries in table */
193: uint32 removedCount; /* removed entry sentinels in table */
194: uint32 generation; /* entry storage generation number */
195: char *entryStore; /* entry storage */
196: #ifdef JS_DHASHMETER
197: struct JSDHashStats {
198: uint32 searches; /* total number of table searches */
199: uint32 steps; /* hash chain links traversed */
200: uint32 hits; /* searches that found key */
201: uint32 misses; /* searches that didn't find key */
202: uint32 lookups; /* number of JS_DHASH_LOOKUPs */
203: uint32 addMisses; /* adds that miss, and do work */
204: uint32 addOverRemoved; /* adds that recycled a removed entry */
205: uint32 addHits; /* adds that hit an existing entry */
206: uint32 addFailures; /* out-of-memory during add growth */
207: uint32 removeHits; /* removes that hit, and do work */
208: uint32 removeMisses; /* useless removes that miss */
209: uint32 removeFrees; /* removes that freed entry directly */
210: uint32 removeEnums; /* removes done by Enumerate */
211: uint32 grows; /* table expansions */
212: uint32 shrinks; /* table contractions */
213: uint32 compresses; /* table compressions */
214: uint32 enumShrinks; /* contractions after Enumerate */
215: } stats;
216: #endif
217: };
218:
219: /*
220: * Size in entries (gross, not net of free and removed sentinels) for table.
221: * We store hashShift rather than sizeLog2 to optimize the collision-free case
222: * in SearchTable.
223: */
224: #define JS_DHASH_TABLE_SIZE(table) JS_BIT(JS_DHASH_BITS - (table)->hashShift)
225:
226: /*
227: * Table space at entryStore is allocated and freed using these callbacks.
228: * The allocator should return null on error only (not if called with nbytes
229: * equal to 0; but note that jsdhash.c code will never call with 0 nbytes).
230: */
231: typedef void *
232: (* JS_DLL_CALLBACK JSDHashAllocTable)(JSDHashTable *table, uint32 nbytes);
233:
234: typedef void
235: (* JS_DLL_CALLBACK JSDHashFreeTable) (JSDHashTable *table, void *ptr);
236:
237: /*
238: * When a table grows or shrinks, each entry is queried for its key using this
239: * callback. NB: in that event, entry is not in table any longer; it's in the
240: * old entryStore vector, which is due to be freed once all entries have been
241: * moved via moveEntry callbacks.
242: */
243: typedef const void *
244: (* JS_DLL_CALLBACK JSDHashGetKey) (JSDHashTable *table,
245: JSDHashEntryHdr *entry);
246:
247: /*
248: * Compute the hash code for a given key to be looked up, added, or removed
249: * from table. A hash code may have any JSDHashNumber value.
250: */
251: typedef JSDHashNumber
252: (* JS_DLL_CALLBACK JSDHashHashKey) (JSDHashTable *table, const void *key);
253:
254: /*
255: * Compare the key identifying entry in table with the provided key parameter.
256: * Return JS_TRUE if keys match, JS_FALSE otherwise.
257: */
258: typedef JSBool
259: (* JS_DLL_CALLBACK JSDHashMatchEntry)(JSDHashTable *table,
260: const JSDHashEntryHdr *entry,
261: const void *key);
262:
263: /*
264: * Copy the data starting at from to the new entry storage at to. Do not add
265: * reference counts for any strong references in the entry, however, as this
266: * is a "move" operation: the old entry storage at from will be freed without
267: * any reference-decrementing callback shortly.
268: */
269: typedef void
270: (* JS_DLL_CALLBACK JSDHashMoveEntry)(JSDHashTable *table,
271: const JSDHashEntryHdr *from,
272: JSDHashEntryHdr *to);
273:
274: /*
275: * Clear the entry and drop any strong references it holds. This callback is
276: * invoked during a JS_DHASH_REMOVE operation (see below for operation codes),
277: * but only if the given key is found in the table.
278: */
279: typedef void
280: (* JS_DLL_CALLBACK JSDHashClearEntry)(JSDHashTable *table,
281: JSDHashEntryHdr *entry);
282:
283: /*
284: * Called when a table (whether allocated dynamically by itself, or nested in
285: * a larger structure, or allocated on the stack) is finished. This callback
286: * allows table->ops-specific code to finalize table->data.
287: */
288: typedef void
289: (* JS_DLL_CALLBACK JSDHashFinalize) (JSDHashTable *table);
290:
291: /*
292: * Initialize a new entry, apart from keyHash. This function is called when
293: * JS_DHashTableOperate's JS_DHASH_ADD case finds no existing entry for the
294: * given key, and must add a new one. At that point, entry->keyHash is not
295: * set yet, to avoid claiming the last free entry in a severely overloaded
296: * table.
297: */
298: typedef JSBool
299: (* JS_DLL_CALLBACK JSDHashInitEntry)(JSDHashTable *table,
300: JSDHashEntryHdr *entry,
301: const void *key);
302:
303: /*
304: * Finally, the "vtable" structure for JSDHashTable. The first eight hooks
305: * must be provided by implementations; they're called unconditionally by the
306: * generic jsdhash.c code. Hooks after these may be null.
307: *
308: * Summary of allocation-related hook usage with C++ placement new emphasis:
309: * allocTable Allocate raw bytes with malloc, no ctors run.
310: * freeTable Free raw bytes with free, no dtors run.
311: * initEntry Call placement new using default key-based ctor.
312: * Return JS_TRUE on success, JS_FALSE on error.
313: * moveEntry Call placement new using copy ctor, run dtor on old
314: * entry storage.
315: * clearEntry Run dtor on entry.
316: * finalize Stub unless table->data was initialized and needs to
317: * be finalized.
318: *
319: * Note the reason why initEntry is optional: the default hooks (stubs) clear
320: * entry storage: On successful JS_DHashTableOperate(tbl, key, JS_DHASH_ADD),
321: * the returned entry pointer addresses an entry struct whose keyHash member
322: * has been set non-zero, but all other entry members are still clear (null).
323: * JS_DHASH_ADD callers can test such members to see whether the entry was
324: * newly created by the JS_DHASH_ADD call that just succeeded. If placement
325: * new or similar initialization is required, define an initEntry hook. Of
326: * course, the clearEntry hook must zero or null appropriately.
327: *
328: * XXX assumes 0 is null for pointer types.
329: */
330: struct JSDHashTableOps {
331: /* Mandatory hooks. All implementations must provide these. */
332: JSDHashAllocTable allocTable;
333: JSDHashFreeTable freeTable;
334: JSDHashGetKey getKey;
335: JSDHashHashKey hashKey;
336: JSDHashMatchEntry matchEntry;
337: JSDHashMoveEntry moveEntry;
338: JSDHashClearEntry clearEntry;
339: JSDHashFinalize finalize;
340:
341: /* Optional hooks start here. If null, these are not called. */
342: JSDHashInitEntry initEntry;
343: };
344:
345: /*
346: * Default implementations for the above ops.
347: */
348: extern JS_PUBLIC_API(void *)
349: JS_DHashAllocTable(JSDHashTable *table, uint32 nbytes);
350:
351: extern JS_PUBLIC_API(void)
352: JS_DHashFreeTable(JSDHashTable *table, void *ptr);
353:
354: extern JS_PUBLIC_API(JSDHashNumber)
355: JS_DHashStringKey(JSDHashTable *table, const void *key);
356:
357: /* A minimal entry contains a keyHash header and a void key pointer. */
358: struct JSDHashEntryStub {
359: JSDHashEntryHdr hdr;
360: const void *key;
361: };
362:
363: extern JS_PUBLIC_API(const void *)
364: JS_DHashGetKeyStub(JSDHashTable *table, JSDHashEntryHdr *entry);
365:
366: extern JS_PUBLIC_API(JSDHashNumber)
367: JS_DHashVoidPtrKeyStub(JSDHashTable *table, const void *key);
368:
369: extern JS_PUBLIC_API(JSBool)
370: JS_DHashMatchEntryStub(JSDHashTable *table,
371: const JSDHashEntryHdr *entry,
372: const void *key);
373:
374: extern JS_PUBLIC_API(JSBool)
375: JS_DHashMatchStringKey(JSDHashTable *table,
376: const JSDHashEntryHdr *entry,
377: const void *key);
378:
379: extern JS_PUBLIC_API(void)
380: JS_DHashMoveEntryStub(JSDHashTable *table,
381: const JSDHashEntryHdr *from,
382: JSDHashEntryHdr *to);
383:
384: extern JS_PUBLIC_API(void)
385: JS_DHashClearEntryStub(JSDHashTable *table, JSDHashEntryHdr *entry);
386:
387: extern JS_PUBLIC_API(void)
388: JS_DHashFreeStringKey(JSDHashTable *table, JSDHashEntryHdr *entry);
389:
390: extern JS_PUBLIC_API(void)
391: JS_DHashFinalizeStub(JSDHashTable *table);
392:
393: /*
394: * If you use JSDHashEntryStub or a subclass of it as your entry struct, and
395: * if your entries move via memcpy and clear via memset(0), you can use these
396: * stub operations.
397: */
398: extern JS_PUBLIC_API(const JSDHashTableOps *)
399: JS_DHashGetStubOps(void);
400:
401: /*
402: * Dynamically allocate a new JSDHashTable using malloc, initialize it using
403: * JS_DHashTableInit, and return its address. Return null on malloc failure.
404: * Note that the entry storage at table->entryStore will be allocated using
405: * the ops->allocTable callback.
406: */
407: extern JS_PUBLIC_API(JSDHashTable *)
408: JS_NewDHashTable(const JSDHashTableOps *ops, void *data, uint32 entrySize,
409: uint32 capacity);
410:
411: /*
412: * Finalize table's data, free its entry storage (via table->ops->freeTable),
413: * and return the memory starting at table to the malloc heap.
414: */
415: extern JS_PUBLIC_API(void)
416: JS_DHashTableDestroy(JSDHashTable *table);
417:
418: /*
419: * Initialize table with ops, data, entrySize, and capacity. Capacity is a
420: * guess for the smallest table size at which the table will usually be less
421: * than 75% loaded (the table will grow or shrink as needed; capacity serves
422: * only to avoid inevitable early growth from JS_DHASH_MIN_SIZE).
423: */
424: extern JS_PUBLIC_API(JSBool)
425: JS_DHashTableInit(JSDHashTable *table, const JSDHashTableOps *ops, void *data,
426: uint32 entrySize, uint32 capacity);
427:
428: /*
429: * Set maximum and minimum alpha for table. The defaults are 0.75 and .25.
430: * maxAlpha must be in [0.5, 0.9375] for the default JS_DHASH_MIN_SIZE; or if
431: * MinSize=JS_DHASH_MIN_SIZE <= 256, in [0.5, (float)(MinSize-1)/MinSize]; or
432: * else in [0.5, 255.0/256]. minAlpha must be in [0, maxAlpha / 2), so that
433: * we don't shrink on the very next remove after growing a table upon adding
434: * an entry that brings entryCount past maxAlpha * tableSize.
435: */
436: JS_PUBLIC_API(void)
437: JS_DHashTableSetAlphaBounds(JSDHashTable *table,
438: float maxAlpha,
439: float minAlpha);
440:
441: /*
442: * Call this macro with k, the number of pointer-sized words wasted per entry
443: * under chaining, to compute the minimum alpha at which double hashing still
444: * beats chaining.
445: */
446: #define JS_DHASH_MIN_ALPHA(table, k) \
447: ((float)((table)->entrySize / sizeof(void *) - 1) \
448: / ((table)->entrySize / sizeof(void *) + (k)))
449:
450: /*
451: * Finalize table's data, free its entry storage using table->ops->freeTable,
452: * and leave its members unchanged from their last live values (which leaves
453: * pointers dangling). If you want to burn cycles clearing table, it's up to
454: * your code to call memset.
455: */
456: extern JS_PUBLIC_API(void)
457: JS_DHashTableFinish(JSDHashTable *table);
458:
459: /*
460: * To consolidate keyHash computation and table grow/shrink code, we use a
461: * single entry point for lookup, add, and remove operations. The operation
462: * codes are declared here, along with codes returned by JSDHashEnumerator
463: * functions, which control JS_DHashTableEnumerate's behavior.
464: */
465: typedef enum JSDHashOperator {
466: JS_DHASH_LOOKUP = 0, /* lookup entry */
467: JS_DHASH_ADD = 1, /* add entry */
468: JS_DHASH_REMOVE = 2, /* remove entry, or enumerator says remove */
469: JS_DHASH_NEXT = 0, /* enumerator says continue */
470: JS_DHASH_STOP = 1 /* enumerator says stop */
471: } JSDHashOperator;
472:
473: /*
474: * To lookup a key in table, call:
475: *
476: * entry = JS_DHashTableOperate(table, key, JS_DHASH_LOOKUP);
477: *
478: * If JS_DHASH_ENTRY_IS_BUSY(entry) is true, key was found and it identifies
479: * entry. If JS_DHASH_ENTRY_IS_FREE(entry) is true, key was not found.
480: *
481: * To add an entry identified by key to table, call:
482: *
483: * entry = JS_DHashTableOperate(table, key, JS_DHASH_ADD);
484: *
485: * If entry is null upon return, then either the table is severely overloaded,
486: * and memory can't be allocated for entry storage via table->ops->allocTable;
487: * Or if table->ops->initEntry is non-null, the table->ops->initEntry op may
488: * have returned false.
489: *
490: * Otherwise, entry->keyHash has been set so that JS_DHASH_ENTRY_IS_BUSY(entry)
491: * is true, and it is up to the caller to initialize the key and value parts
492: * of the entry sub-type, if they have not been set already (i.e. if entry was
493: * not already in the table, and if the optional initEntry hook was not used).
494: *
495: * To remove an entry identified by key from table, call:
496: *
497: * (void) JS_DHashTableOperate(table, key, JS_DHASH_REMOVE);
498: *
499: * If key's entry is found, it is cleared (via table->ops->clearEntry) and
500: * the entry is marked so that JS_DHASH_ENTRY_IS_FREE(entry). This operation
501: * returns null unconditionally; you should ignore its return value.
502: */
503: extern JS_PUBLIC_API(JSDHashEntryHdr *)
504: JS_DHashTableOperate(JSDHashTable *table, const void *key, JSDHashOperator op);
505:
506: /*
507: * Remove an entry already accessed via LOOKUP or ADD.
508: *
509: * NB: this is a "raw" or low-level routine, intended to be used only where
510: * the inefficiency of a full JS_DHashTableOperate (which rehashes in order
511: * to find the entry given its key) is not tolerable. This function does not
512: * shrink the table if it is underloaded. It does not update stats #ifdef
513: * JS_DHASHMETER, either.
514: */
515: extern JS_PUBLIC_API(void)
516: JS_DHashTableRawRemove(JSDHashTable *table, JSDHashEntryHdr *entry);
517:
518: /*
519: * Enumerate entries in table using etor:
520: *
521: * count = JS_DHashTableEnumerate(table, etor, arg);
522: *
523: * JS_DHashTableEnumerate calls etor like so:
524: *
525: * op = etor(table, entry, number, arg);
526: *
527: * where number is a zero-based ordinal assigned to live entries according to
528: * their order in table->entryStore.
529: *
530: * The return value, op, is treated as a set of flags. If op is JS_DHASH_NEXT,
531: * then continue enumerating. If op contains JS_DHASH_REMOVE, then clear (via
532: * table->ops->clearEntry) and free entry. Then we check whether op contains
533: * JS_DHASH_STOP; if so, stop enumerating and return the number of live entries
534: * that were enumerated so far. Return the total number of live entries when
535: * enumeration completes normally.
536: *
537: * If etor calls JS_DHashTableOperate on table with op != JS_DHASH_LOOKUP, it
538: * must return JS_DHASH_STOP; otherwise undefined behavior results.
539: *
540: * If any enumerator returns JS_DHASH_REMOVE, table->entryStore may be shrunk
541: * or compressed after enumeration, but before JS_DHashTableEnumerate returns.
542: * Such an enumerator therefore can't safely set aside entry pointers, but an
543: * enumerator that never returns JS_DHASH_REMOVE can set pointers to entries
544: * aside, e.g., to avoid copying live entries into an array of the entry type.
545: * Copying entry pointers is cheaper, and safe so long as the caller of such a
546: * "stable" Enumerate doesn't use the set-aside pointers after any call either
547: * to PL_DHashTableOperate, or to an "unstable" form of Enumerate, which might
548: * grow or shrink entryStore.
549: *
550: * If your enumerator wants to remove certain entries, but set aside pointers
551: * to other entries that it retains, it can use JS_DHashTableRawRemove on the
552: * entries to be removed, returning JS_DHASH_NEXT to skip them. Likewise, if
553: * you want to remove entries, but for some reason you do not want entryStore
554: * to be shrunk or compressed, you can call JS_DHashTableRawRemove safely on
555: * the entry being enumerated, rather than returning JS_DHASH_REMOVE.
556: */
557: typedef JSDHashOperator
558: (* JS_DLL_CALLBACK JSDHashEnumerator)(JSDHashTable *table, JSDHashEntryHdr *hdr,
559: uint32 number, void *arg);
560:
561: extern JS_PUBLIC_API(uint32)
562: JS_DHashTableEnumerate(JSDHashTable *table, JSDHashEnumerator etor, void *arg);
563:
564: #ifdef JS_DHASHMETER
565: #include <stdio.h>
566:
567: extern JS_PUBLIC_API(void)
568: JS_DHashTableDumpMeter(JSDHashTable *table, JSDHashEnumerator dump, FILE *fp);
569: #endif
570:
571: JS_END_EXTERN_C
572:
573: #endif /* jsdhash_h___ */
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