The Android Open Source Project | f6c3871 | 2009-03-03 19:28:47 -0800 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2008 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | /* |
| 17 | * String interning. |
| 18 | */ |
| 19 | #include "Dalvik.h" |
| 20 | |
| 21 | #include <stdlib.h> |
| 22 | |
| 23 | #define INTERN_STRING_IMMORTAL_BIT (1<<0) |
| 24 | #define SET_IMMORTAL_BIT(strObj) \ |
| 25 | ((uintptr_t)(strObj) | INTERN_STRING_IMMORTAL_BIT) |
| 26 | #define STRIP_IMMORTAL_BIT(strObj) \ |
| 27 | ((uintptr_t)(strObj) & ~INTERN_STRING_IMMORTAL_BIT) |
| 28 | #define IS_IMMORTAL(strObj) \ |
| 29 | ((uintptr_t)(strObj) & INTERN_STRING_IMMORTAL_BIT) |
| 30 | |
| 31 | |
| 32 | /* |
| 33 | * Prep string interning. |
| 34 | */ |
| 35 | bool dvmStringInternStartup(void) |
| 36 | { |
| 37 | gDvm.internedStrings = dvmHashTableCreate(256, NULL); |
| 38 | if (gDvm.internedStrings == NULL) |
| 39 | return false; |
| 40 | |
| 41 | return true; |
| 42 | } |
| 43 | |
| 44 | /* |
| 45 | * Chuck the intern list. |
| 46 | * |
| 47 | * The contents of the list are StringObjects that live on the GC heap. |
| 48 | */ |
| 49 | void dvmStringInternShutdown(void) |
| 50 | { |
| 51 | dvmHashTableFree(gDvm.internedStrings); |
| 52 | gDvm.internedStrings = NULL; |
| 53 | } |
| 54 | |
| 55 | |
| 56 | /* |
| 57 | * Compare two string objects that may have INTERN_STRING_IMMORTAL_BIT |
| 58 | * set in their pointer values. |
| 59 | */ |
| 60 | static int hashcmpImmortalStrings(const void* vstrObj1, const void* vstrObj2) |
| 61 | { |
| 62 | return dvmHashcmpStrings((const void*) STRIP_IMMORTAL_BIT(vstrObj1), |
| 63 | (const void*) STRIP_IMMORTAL_BIT(vstrObj2)); |
| 64 | } |
| 65 | |
| 66 | static StringObject* lookupInternedString(StringObject* strObj, bool immortal) |
| 67 | { |
| 68 | StringObject* found; |
| 69 | u4 hash; |
| 70 | |
| 71 | assert(strObj != NULL); |
| 72 | hash = dvmComputeStringHash(strObj); |
| 73 | |
| 74 | if (false) { |
| 75 | char* debugStr = dvmCreateCstrFromString(strObj); |
| 76 | LOGV("+++ dvmLookupInternedString searching for '%s'\n", debugStr); |
| 77 | free(debugStr); |
| 78 | } |
| 79 | |
| 80 | if (immortal) { |
| 81 | strObj = (StringObject*) SET_IMMORTAL_BIT(strObj); |
| 82 | } |
| 83 | |
| 84 | dvmHashTableLock(gDvm.internedStrings); |
| 85 | |
| 86 | found = (StringObject*) dvmHashTableLookup(gDvm.internedStrings, |
| 87 | hash, strObj, hashcmpImmortalStrings, true); |
| 88 | if (immortal && !IS_IMMORTAL(found)) { |
| 89 | /* Make this entry immortal. We have to use the existing object |
| 90 | * because, as an interned string, it's not allowed to change. |
| 91 | * |
| 92 | * There's no way to get a pointer to the actual hash table entry, |
| 93 | * so the only way to modify the existing entry is to remove, |
| 94 | * modify, and re-add it. |
| 95 | */ |
| 96 | dvmHashTableRemove(gDvm.internedStrings, hash, found); |
| 97 | found = (StringObject*) SET_IMMORTAL_BIT(found); |
| 98 | found = (StringObject*) dvmHashTableLookup(gDvm.internedStrings, |
| 99 | hash, found, hashcmpImmortalStrings, true); |
| 100 | assert(IS_IMMORTAL(found)); |
| 101 | } |
| 102 | |
| 103 | dvmHashTableUnlock(gDvm.internedStrings); |
| 104 | |
| 105 | //if (found == strObj) |
| 106 | // LOGVV("+++ added string\n"); |
| 107 | return (StringObject*) STRIP_IMMORTAL_BIT(found); |
| 108 | } |
| 109 | |
| 110 | /* |
| 111 | * Find an entry in the interned string list. |
| 112 | * |
| 113 | * If the string doesn't already exist, the StringObject is added to |
| 114 | * the list. Otherwise, the existing entry is returned. |
| 115 | */ |
| 116 | StringObject* dvmLookupInternedString(StringObject* strObj) |
| 117 | { |
| 118 | return lookupInternedString(strObj, false); |
| 119 | } |
| 120 | |
| 121 | /* |
| 122 | * Same as dvmLookupInternedString(), but guarantees that the |
| 123 | * returned string is immortal. |
| 124 | */ |
| 125 | StringObject* dvmLookupImmortalInternedString(StringObject* strObj) |
| 126 | { |
| 127 | return lookupInternedString(strObj, true); |
| 128 | } |
| 129 | |
| 130 | /* |
| 131 | * Mark all immortal interned string objects so that they don't |
| 132 | * get collected by the GC. Non-immortal strings may or may not |
| 133 | * get marked by other references. |
| 134 | */ |
| 135 | static int markStringObject(void* strObj, void* arg) |
| 136 | { |
| 137 | UNUSED_PARAMETER(arg); |
| 138 | |
| 139 | if (IS_IMMORTAL(strObj)) { |
| 140 | dvmMarkObjectNonNull((Object*) STRIP_IMMORTAL_BIT(strObj)); |
| 141 | } |
| 142 | return 0; |
| 143 | } |
| 144 | |
| 145 | void dvmGcScanInternedStrings() |
| 146 | { |
| 147 | /* It's possible for a GC to happen before dvmStringInternStartup() |
| 148 | * is called. |
| 149 | */ |
| 150 | if (gDvm.internedStrings != NULL) { |
| 151 | dvmHashTableLock(gDvm.internedStrings); |
| 152 | dvmHashForeach(gDvm.internedStrings, markStringObject, NULL); |
| 153 | dvmHashTableUnlock(gDvm.internedStrings); |
| 154 | } |
| 155 | } |
| 156 | |
| 157 | /* |
| 158 | * Called by the GC after all reachable objects have been |
| 159 | * marked. isUnmarkedObject is a function suitable for passing |
| 160 | * to dvmHashForeachRemove(); it must strip the low bits from |
| 161 | * its pointer argument to deal with the immortal bit, though. |
| 162 | */ |
| 163 | void dvmGcDetachDeadInternedStrings(int (*isUnmarkedObject)(void *)) |
| 164 | { |
| 165 | /* It's possible for a GC to happen before dvmStringInternStartup() |
| 166 | * is called. |
| 167 | */ |
| 168 | if (gDvm.internedStrings != NULL) { |
| 169 | dvmHashTableLock(gDvm.internedStrings); |
| 170 | dvmHashForeachRemove(gDvm.internedStrings, isUnmarkedObject); |
| 171 | dvmHashTableUnlock(gDvm.internedStrings); |
| 172 | } |
| 173 | } |