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1.1 ! root 1: /* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- ! 2: * ! 3: * The contents of this file are subject to the Netscape Public ! 4: * License Version 1.1 (the "License"); you may not use this file ! 5: * except in compliance with the License. You may obtain a copy of ! 6: * the License at http://www.mozilla.org/NPL/ ! 7: * ! 8: * Software distributed under the License is distributed on an "AS ! 9: * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or ! 10: * implied. See the License for the specific language governing ! 11: * rights and limitations under the License. ! 12: * ! 13: * The Original Code is Mozilla Communicator client code, released ! 14: * March 31, 1998. ! 15: * ! 16: * The Initial Developer of the Original Code is Netscape ! 17: * Communications Corporation. Portions created by Netscape are ! 18: * Copyright (C) 1998 Netscape Communications Corporation. All ! 19: * Rights Reserved. ! 20: * ! 21: * Contributor(s): ! 22: * ! 23: * Alternatively, the contents of this file may be used under the ! 24: * terms of the GNU Public License (the "GPL"), in which case the ! 25: * provisions of the GPL are applicable instead of those above. ! 26: * If you wish to allow use of your version of this file only ! 27: * under the terms of the GPL and not to allow others to use your ! 28: * version of this file under the NPL, indicate your decision by ! 29: * deleting the provisions above and replace them with the notice ! 30: * and other provisions required by the GPL. If you do not delete ! 31: * the provisions above, a recipient may use your version of this ! 32: * file under either the NPL or the GPL. ! 33: */ ! 34: ! 35: #ifndef jsscope_h___ ! 36: #define jsscope_h___ ! 37: /* ! 38: * JS symbol tables. ! 39: */ ! 40: #include "jstypes.h" ! 41: #include "jsobj.h" ! 42: #include "jsprvtd.h" ! 43: #include "jspubtd.h" ! 44: ! 45: #ifdef JS_THREADSAFE ! 46: # include "jslock.h" ! 47: #endif ! 48: ! 49: /* ! 50: * Given P independent, non-unique properties each of size S words mapped by ! 51: * all scopes in a runtime, construct a property tree of N nodes each of size ! 52: * S+L words (L for tree linkage). A nominal L value is 2 for leftmost-child ! 53: * and right-sibling links. We hope that the N < P by enough that the space ! 54: * overhead of L, and the overhead of scope entries pointing at property tree ! 55: * nodes, is worth it. ! 56: * ! 57: * The tree construction goes as follows. If any empty scope in the runtime ! 58: * has a property X added to it, find or create a node under the tree root ! 59: * labeled X, and set scope->lastProp to point at that node. If any non-empty ! 60: * scope whose most recently added property is labeled Y has another property ! 61: * labeled Z added, find or create a node for Z under the node that was added ! 62: * for Y, and set scope->lastProp to point at that node. ! 63: * ! 64: * A property is labeled by its members' values: id, getter, setter, slot, ! 65: * attributes, tiny or short id, and a field telling for..in order. Note that ! 66: * labels are not unique in the tree, but they are unique among a node's kids ! 67: * (barring rare and benign multi-threaded race condition outcomes, see below) ! 68: * and along any ancestor line from the tree root to a given leaf node (except ! 69: * for the hard case of duplicate formal parameters to a function). ! 70: * ! 71: * Thus the root of the tree represents all empty scopes, and the first ply ! 72: * of the tree represents all scopes containing one property, etc. Each node ! 73: * in the tree can stand for any number of scopes having the same ordered set ! 74: * of properties, where that node was the last added to the scope. (We need ! 75: * not store the root of the tree as a node, and do not -- all we need are ! 76: * links to its kids.) ! 77: * ! 78: * Sidebar on for..in loop order: ECMA requires no particular order, but this ! 79: * implementation has promised and delivered property definition order, and ! 80: * compatibility is king. We could use an order number per property, which ! 81: * would require a sort in js_Enumerate, and an entry order generation number ! 82: * per scope. An order number beats a list, which should be doubly-linked for ! 83: * O(1) delete. An even better scheme is to use a parent link in the property ! 84: * tree, so that the ancestor line can be iterated from scope->lastProp when ! 85: * filling in a JSIdArray from back to front. This parent link also helps the ! 86: * GC to sweep properties iteratively. ! 87: * ! 88: * What if a property Y is deleted from a scope? If Y is the last property in ! 89: * the scope, we simply adjust the scope's lastProp member after we remove the ! 90: * scope's hash-table entry pointing at that property node. The parent link ! 91: * mentioned in the for..in sidebar above makes this adjustment O(1). But if ! 92: * Y comes between X and Z in the scope, then we might have to "fork" the tree ! 93: * at X, leaving X->Y->Z in case other scopes have those properties added in ! 94: * that order; and to finish the fork, we'd add a node labeled Z with the path ! 95: * X->Z, if it doesn't exist. This could lead to lots of extra nodes, and to ! 96: * O(n^2) growth when deleting lots of properties. ! 97: * ! 98: * Rather, for O(1) growth all around, we should share the path X->Y->Z among ! 99: * scopes having those three properties added in that order, and among scopes ! 100: * having only X->Z where Y was deleted. All such scopes have a lastProp that ! 101: * points to the Z child of Y. But a scope in which Y was deleted does not ! 102: * have a table entry for Y, and when iterating that scope by traversing the ! 103: * ancestor line from Z, we will have to test for a table entry for each node, ! 104: * skipping nodes that lack entries. ! 105: * ! 106: * What if we add Y again? X->Y->Z->Y is wrong and we'll enumerate Y twice. ! 107: * Therefore we must fork in such a case, if not earlier. Because delete is ! 108: * "bursty", we should not fork eagerly. Delaying a fork till we are at risk ! 109: * of adding Y after it was deleted already requires a flag in the JSScope, to ! 110: * wit, SCOPE_MIDDLE_DELETE. ! 111: * ! 112: * What about thread safety? If the property tree operations done by requests ! 113: * are find-node and insert-node, then the only hazard is duplicate insertion. ! 114: * This is harmless except for minor bloat. When all requests have ended or ! 115: * been suspended, the GC is free to sweep the tree after marking all nodes ! 116: * reachable from scopes, performing remove-node operations as needed. Note ! 117: * also that the stable storage of the property nodes during active requests ! 118: * permits the property cache (see jsinterp.h) to dereference JSScopeProperty ! 119: * weak references safely. ! 120: * ! 121: * Is the property tree worth it compared to property storage in each table's ! 122: * entries? To decide, we must find the relation <> between the words used ! 123: * with a property tree and the words required without a tree. ! 124: * ! 125: * Model all scopes as one super-scope of capacity T entries (T a power of 2). ! 126: * Let alpha be the load factor of this double hash-table. With the property ! 127: * tree, each entry in the table is a word-sized pointer to a node that can be ! 128: * shared by many scopes. But all such pointers are overhead compared to the ! 129: * situation without the property tree, where the table stores property nodes ! 130: * directly, as entries each of size S words. With the property tree, we need ! 131: * L=2 extra words per node for siblings and kids pointers. Without the tree, ! 132: * (1-alpha)*S*T words are wasted on free or removed sentinel-entries required ! 133: * by double hashing. ! 134: * ! 135: * Therefore, ! 136: * ! 137: * (property tree) <> (no property tree) ! 138: * N*(S+L) + T <> S*T ! 139: * N*(S+L) + T <> P*S + (1-alpha)*S*T ! 140: * N*(S+L) + alpha*T + (1-alpha)*T <> P*S + (1-alpha)*S*T ! 141: * ! 142: * Note that P is alpha*T by definition, so ! 143: * ! 144: * N*(S+L) + P + (1-alpha)*T <> P*S + (1-alpha)*S*T ! 145: * N*(S+L) <> P*S - P + (1-alpha)*S*T - (1-alpha)*T ! 146: * N*(S+L) <> (P + (1-alpha)*T) * (S-1) ! 147: * N*(S+L) <> (P + (1-alpha)*P/alpha) * (S-1) ! 148: * N*(S+L) <> P * (1/alpha) * (S-1) ! 149: * ! 150: * Let N = P*beta for a compression ratio beta, beta <= 1: ! 151: * ! 152: * P*beta*(S+L) <> P * (1/alpha) * (S-1) ! 153: * beta*(S+L) <> (S-1)/alpha ! 154: * beta <> (S-1)/((S+L)*alpha) ! 155: * ! 156: * For S = 6 (32-bit architectures) and L = 2, the property tree wins iff ! 157: * ! 158: * beta < 5/(8*alpha) ! 159: * ! 160: * We ensure that alpha <= .75, so the property tree wins if beta < .83_. An ! 161: * average beta from recent Mozilla browser startups was around .6. ! 162: * ! 163: * Can we reduce L? Observe that the property tree degenerates into a list of ! 164: * lists if at most one property Y follows X in all scopes. In or near such a ! 165: * case, we waste a word on the right-sibling link outside of the root ply of ! 166: * the tree. Note also that the root ply tends to be large, so O(n^2) growth ! 167: * searching it is likely, indicating the need for hashing (but with increased ! 168: * thread safety costs). ! 169: * ! 170: * If only K out of N nodes in the property tree have more than one child, we ! 171: * could eliminate the sibling link and overlay a children list or hash-table ! 172: * pointer on the leftmost-child link (which would then be either null or an ! 173: * only-child link; the overlay could be tagged in the low bit of the pointer, ! 174: * or flagged elsewhere in the property tree node, although such a flag must ! 175: * not be considered when comparing node labels during tree search). ! 176: * ! 177: * For such a system, L = 1 + (K * averageChildrenTableSize) / N instead of 2. ! 178: * If K << N, L approaches 1 and the property tree wins if beta < .95. ! 179: * ! 180: * We observe that fan-out below the root ply of the property tree appears to ! 181: * have extremely low degree (see the MeterPropertyTree code that histograms ! 182: * child-counts in jsscope.c), so instead of a hash-table we use a linked list ! 183: * of child node pointer arrays ("kid chunks"). The details are isolated in ! 184: * jsscope.c; others must treat JSScopeProperty.kids as opaque. We leave it ! 185: * strongly typed for debug-ability of the common (null or one-kid) cases. ! 186: * ! 187: * One final twist (can you stand it?): the mean number of entries per scope ! 188: * in Mozilla is < 5, with a large standard deviation (~8). Instead of always ! 189: * allocating scope->table, we leave it null while initializing all the other ! 190: * scope members as if it were non-null and minimal-length. Until a property ! 191: * is added that crosses the threshold of 6 or more entries for hashing, or ! 192: * until a "middle delete" occurs, we use linear search from scope->lastProp ! 193: * to find a given id, and save on the space overhead of a hash table. ! 194: */ ! 195: ! 196: struct JSScope { ! 197: JSObjectMap map; /* base class state */ ! 198: JSObject *object; /* object that owns this scope */ ! 199: uint16 flags; /* flags, see below */ ! 200: int16 hashShift; /* multiplicative hash shift */ ! 201: uint32 entryCount; /* number of entries in table */ ! 202: uint32 removedCount; /* removed entry sentinels in table */ ! 203: JSScopeProperty **table; /* table of ptrs to shared tree nodes */ ! 204: JSScopeProperty *lastProp; /* pointer to last property added */ ! 205: #ifdef JS_THREADSAFE ! 206: JSContext *ownercx; /* creating context, NULL if shared */ ! 207: JSThinLock lock; /* binary semaphore protecting scope */ ! 208: union { /* union lockful and lock-free state: */ ! 209: jsrefcount count; /* lock entry count for reentrancy */ ! 210: JSScope *link; /* next link in rt->scopeSharingTodo */ ! 211: } u; ! 212: #ifdef DEBUG ! 213: const char *file[4]; /* file where lock was (re-)taken */ ! 214: unsigned int line[4]; /* line where lock was (re-)taken */ ! 215: #endif ! 216: #endif ! 217: }; ! 218: ! 219: #define OBJ_SCOPE(obj) ((JSScope *)(obj)->map) ! 220: ! 221: /* By definition, hashShift = JS_DHASH_BITS - log2(capacity). */ ! 222: #define SCOPE_CAPACITY(scope) JS_BIT(JS_DHASH_BITS-(scope)->hashShift) ! 223: ! 224: /* Scope flags and some macros to hide them from other files than jsscope.c. */ ! 225: #define SCOPE_MIDDLE_DELETE 0x0001 ! 226: #define SCOPE_SEALED 0x0002 ! 227: ! 228: #define SCOPE_HAD_MIDDLE_DELETE(scope) ((scope)->flags & SCOPE_MIDDLE_DELETE) ! 229: #define SCOPE_SET_MIDDLE_DELETE(scope) ((scope)->flags |= SCOPE_MIDDLE_DELETE) ! 230: #define SCOPE_CLR_MIDDLE_DELETE(scope) ((scope)->flags &= ~SCOPE_MIDDLE_DELETE) ! 231: ! 232: #define SCOPE_IS_SEALED(scope) ((scope)->flags & SCOPE_SEALED) ! 233: #define SCOPE_SET_SEALED(scope) ((scope)->flags |= SCOPE_SEALED) ! 234: #define SCOPE_CLR_SEALED(scope) ((scope)->flags &= ~SCOPE_SEALED) ! 235: ! 236: /* ! 237: * A little information hiding for scope->lastProp, in case it ever becomes ! 238: * a tagged pointer again. ! 239: */ ! 240: #define SCOPE_LAST_PROP(scope) ((scope)->lastProp) ! 241: #define SCOPE_REMOVE_LAST_PROP(scope) ((scope)->lastProp = \ ! 242: (scope)->lastProp->parent) ! 243: ! 244: struct JSScopeProperty { ! 245: jsid id; /* int-tagged jsval/untagged JSAtom* */ ! 246: JSPropertyOp getter; /* getter and setter hooks or objects */ ! 247: JSPropertyOp setter; ! 248: uint32 slot; /* index in obj->slots vector */ ! 249: uint8 attrs; /* attributes, see jsapi.h JSPROP_* */ ! 250: uint8 flags; /* flags, see below for defines */ ! 251: int16 shortid; /* tinyid, or local arg/var index */ ! 252: JSScopeProperty *parent; /* parent node, reverse for..in order */ ! 253: JSScopeProperty *kids; /* null, single child, or a tagged ptr ! 254: to many-kids data structure */ ! 255: }; ! 256: ! 257: /* JSScopeProperty pointer tag bit indicating a collision. */ ! 258: #define SPROP_COLLISION ((jsuword)1) ! 259: #define SPROP_REMOVED ((JSScopeProperty *) SPROP_COLLISION) ! 260: ! 261: /* Macros to get and set sprop pointer values and collision flags. */ ! 262: #define SPROP_IS_FREE(sprop) ((sprop) == NULL) ! 263: #define SPROP_IS_REMOVED(sprop) ((sprop) == SPROP_REMOVED) ! 264: #define SPROP_IS_LIVE(sprop) ((sprop) > SPROP_REMOVED) ! 265: #define SPROP_FLAG_COLLISION(spp,sprop) (*(spp) = (JSScopeProperty *) \ ! 266: ((jsuword)(sprop) | SPROP_COLLISION)) ! 267: #define SPROP_HAD_COLLISION(sprop) ((jsuword)(sprop) & SPROP_COLLISION) ! 268: #define SPROP_FETCH(spp) SPROP_CLEAR_COLLISION(*(spp)) ! 269: ! 270: #define SPROP_CLEAR_COLLISION(sprop) \ ! 271: ((JSScopeProperty *) ((jsuword)(sprop) & ~SPROP_COLLISION)) ! 272: ! 273: #define SPROP_STORE_PRESERVING_COLLISION(spp, sprop) \ ! 274: (*(spp) = (JSScopeProperty *) ((jsuword)(sprop) \ ! 275: | SPROP_HAD_COLLISION(*(spp)))) ! 276: ! 277: /* Bits stored in sprop->flags. */ ! 278: #define SPROP_MARK 0x01 ! 279: #define SPROP_IS_DUPLICATE 0x02 ! 280: #define SPROP_IS_ALIAS 0x04 ! 281: #define SPROP_HAS_SHORTID 0x08 ! 282: ! 283: /* ! 284: * If SPROP_HAS_SHORTID is set in sprop->flags, we use sprop->shortid rather ! 285: * than id when calling sprop's getter or setter. ! 286: */ ! 287: #define SPROP_USERID(sprop) \ ! 288: (((sprop)->flags & SPROP_HAS_SHORTID) ? INT_TO_JSVAL((sprop)->shortid) \ ! 289: : ID_TO_VALUE((sprop)->id)) ! 290: ! 291: #define SPROP_INVALID_SLOT 0xffffffff ! 292: ! 293: #define SPROP_HAS_VALID_SLOT(sprop, scope) \ ! 294: ((sprop)->slot < (scope)->map.freeslot) ! 295: ! 296: #define SPROP_CALL_GETTER(cx,sprop,getter,obj,obj2,vp) \ ! 297: (!(getter) || \ ! 298: (getter)(cx, OBJ_THIS_OBJECT(cx,obj), SPROP_USERID(sprop), vp)) ! 299: #define SPROP_CALL_SETTER(cx,sprop,setter,obj,obj2,vp) \ ! 300: (!(setter) || \ ! 301: (setter)(cx, OBJ_THIS_OBJECT(cx,obj), SPROP_USERID(sprop), vp)) ! 302: ! 303: #define SPROP_GET(cx,sprop,obj,obj2,vp) \ ! 304: (((sprop)->attrs & JSPROP_GETTER) \ ! 305: ? js_InternalGetOrSet(cx, obj, (sprop)->id, \ ! 306: OBJECT_TO_JSVAL((sprop)->getter), JSACC_READ, \ ! 307: 0, 0, vp) \ ! 308: : SPROP_CALL_GETTER(cx, sprop, (sprop)->getter, obj, obj2, vp)) ! 309: ! 310: #define SPROP_SET(cx,sprop,obj,obj2,vp) \ ! 311: (((sprop)->attrs & JSPROP_SETTER) \ ! 312: ? js_InternalGetOrSet(cx, obj, (sprop)->id, \ ! 313: OBJECT_TO_JSVAL((sprop)->setter), JSACC_WRITE, \ ! 314: 1, vp, vp) \ ! 315: : ((sprop)->attrs & JSPROP_GETTER) \ ! 316: ? (JS_ReportErrorNumber(cx, js_GetErrorMessage, NULL, \ ! 317: JSMSG_GETTER_ONLY, NULL), JS_FALSE) \ ! 318: : SPROP_CALL_SETTER(cx, sprop, (sprop)->setter, obj, obj2, vp)) ! 319: ! 320: /* Macro for common expression to test for shared permanent attributes. */ ! 321: #define SPROP_IS_SHARED_PERMANENT(sprop) \ ! 322: ((~(sprop)->attrs & (JSPROP_SHARED | JSPROP_PERMANENT)) == 0) ! 323: ! 324: extern JSScope * ! 325: js_GetMutableScope(JSContext *cx, JSObject *obj); ! 326: ! 327: extern JSScope * ! 328: js_NewScope(JSContext *cx, jsrefcount nrefs, JSObjectOps *ops, JSClass *clasp, ! 329: JSObject *obj); ! 330: ! 331: extern void ! 332: js_DestroyScope(JSContext *cx, JSScope *scope); ! 333: ! 334: #define ID_TO_VALUE(id) (((id) & JSVAL_INT) ? id : ATOM_KEY((JSAtom *)(id))) ! 335: #define HASH_ID(id) (((id) & JSVAL_INT) \ ! 336: ? (jsatomid) JSVAL_TO_INT(id) \ ! 337: : ((JSAtom *)id)->number) ! 338: ! 339: extern JS_FRIEND_API(JSScopeProperty **) ! 340: js_SearchScope(JSScope *scope, jsid id, JSBool adding); ! 341: ! 342: #define SCOPE_GET_PROPERTY(scope, id) \ ! 343: SPROP_FETCH(js_SearchScope(scope, id, JS_FALSE)) ! 344: ! 345: #define SCOPE_HAS_PROPERTY(scope, sprop) \ ! 346: (SCOPE_GET_PROPERTY(scope, (sprop)->id) == (sprop)) ! 347: ! 348: extern JSScopeProperty * ! 349: js_AddScopeProperty(JSContext *cx, JSScope *scope, jsid id, ! 350: JSPropertyOp getter, JSPropertyOp setter, uint32 slot, ! 351: uintN attrs, uintN flags, intN shortid); ! 352: ! 353: extern JSScopeProperty * ! 354: js_ChangeScopePropertyAttrs(JSContext *cx, JSScope *scope, ! 355: JSScopeProperty *sprop, uintN attrs, uintN mask, ! 356: JSPropertyOp getter, JSPropertyOp setter); ! 357: ! 358: extern JSBool ! 359: js_RemoveScopeProperty(JSContext *cx, JSScope *scope, jsid id); ! 360: ! 361: extern void ! 362: js_ClearScope(JSContext *cx, JSScope *scope); ! 363: ! 364: #define MARK_SCOPE_PROPERTY(sprop) ((sprop)->flags |= SPROP_MARK) ! 365: ! 366: extern void ! 367: js_SweepScopeProperties(JSRuntime *rt); ! 368: ! 369: extern JSBool ! 370: js_InitPropertyTree(JSRuntime *rt); ! 371: ! 372: extern void ! 373: js_FinishPropertyTree(JSRuntime *rt); ! 374: ! 375: #endif /* jsscope_h___ */
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