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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: 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
7: * the License. You may obtain a copy of the License at
8: * http://www.mozilla.org/MPL/
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 of the GNU General Public License Version 2 or later (the "GPL"),
27: * or 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 MPL, 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 MPL, 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: #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
53:
54: #ifdef DEBUG_XXXbrendan
55: #define JS_DHASHMETER 1
56: #endif
57:
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)
61:
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
68:
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
75:
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;
82:
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: };
114:
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)
118:
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: };
224:
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)
231:
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);
239:
240: typedef void
241: (* JS_DLL_CALLBACK JSDHashFreeTable) (JSDHashTable *table, void *ptr);
242:
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);
252:
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);
259:
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);
268:
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);
279:
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);
288:
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);
296:
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);
308:
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;
346:
347: /* Optional hooks start here. If null, these are not called. */
348: JSDHashInitEntry initEntry;
349: };
350:
351: /*
352: * Default implementations for the above ops.
353: */
354: extern JS_PUBLIC_API(void *)
355: JS_DHashAllocTable(JSDHashTable *table, uint32 nbytes);
356:
357: extern JS_PUBLIC_API(void)
358: JS_DHashFreeTable(JSDHashTable *table, void *ptr);
359:
360: extern JS_PUBLIC_API(JSDHashNumber)
361: JS_DHashStringKey(JSDHashTable *table, const void *key);
362:
363: /* A minimal entry contains a keyHash header and a void key pointer. */
364: struct JSDHashEntryStub {
365: JSDHashEntryHdr hdr;
366: const void *key;
367: };
368:
369: extern JS_PUBLIC_API(const void *)
370: JS_DHashGetKeyStub(JSDHashTable *table, JSDHashEntryHdr *entry);
371:
372: extern JS_PUBLIC_API(JSDHashNumber)
373: JS_DHashVoidPtrKeyStub(JSDHashTable *table, const void *key);
374:
375: extern JS_PUBLIC_API(JSBool)
376: JS_DHashMatchEntryStub(JSDHashTable *table,
377: const JSDHashEntryHdr *entry,
378: const void *key);
379:
380: extern JS_PUBLIC_API(JSBool)
381: JS_DHashMatchStringKey(JSDHashTable *table,
382: const JSDHashEntryHdr *entry,
383: const void *key);
384:
385: extern JS_PUBLIC_API(void)
386: JS_DHashMoveEntryStub(JSDHashTable *table,
387: const JSDHashEntryHdr *from,
388: JSDHashEntryHdr *to);
389:
390: extern JS_PUBLIC_API(void)
391: JS_DHashClearEntryStub(JSDHashTable *table, JSDHashEntryHdr *entry);
392:
393: extern JS_PUBLIC_API(void)
394: JS_DHashFreeStringKey(JSDHashTable *table, JSDHashEntryHdr *entry);
395:
396: extern JS_PUBLIC_API(void)
397: JS_DHashFinalizeStub(JSDHashTable *table);
398:
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);
406:
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);
416:
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);
423:
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);
433:
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: JS_PUBLIC_API(void)
443: JS_DHashTableSetAlphaBounds(JSDHashTable *table,
444: float maxAlpha,
445: float minAlpha);
446:
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)))
455:
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);
464:
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;
478:
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);
511:
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);
523:
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);
566:
567: extern JS_PUBLIC_API(uint32)
568: JS_DHashTableEnumerate(JSDHashTable *table, JSDHashEnumerator etor, void *arg);
569:
570: #ifdef JS_DHASHMETER
571: #include <stdio.h>
572:
573: extern JS_PUBLIC_API(void)
574: JS_DHashTableDumpMeter(JSDHashTable *table, JSDHashEnumerator dump, FILE *fp);
575: #endif
576:
577: JS_END_EXTERN_C
578:
579: #endif /* jsdhash_h___ */
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