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Intern.c
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Intern.c
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/*
* Copyright (C) 2008 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/*
* String interning.
*/
#include "Dalvik.h"
#include <stdlib.h>
#define INTERN_STRING_IMMORTAL_BIT (1<<0)
#define SET_IMMORTAL_BIT(strObj) \
((uintptr_t)(strObj) | INTERN_STRING_IMMORTAL_BIT)
#define STRIP_IMMORTAL_BIT(strObj) \
((uintptr_t)(strObj) & ~INTERN_STRING_IMMORTAL_BIT)
#define IS_IMMORTAL(strObj) \
((uintptr_t)(strObj) & INTERN_STRING_IMMORTAL_BIT)
/*
* Prep string interning.
*/
bool dvmStringInternStartup(void)
{
gDvm.internedStrings = dvmHashTableCreate(256, NULL);
if (gDvm.internedStrings == NULL)
return false;
return true;
}
/*
* Chuck the intern list.
*
* The contents of the list are StringObjects that live on the GC heap.
*/
void dvmStringInternShutdown(void)
{
dvmHashTableFree(gDvm.internedStrings);
gDvm.internedStrings = NULL;
}
/*
* Compare two string objects that may have INTERN_STRING_IMMORTAL_BIT
* set in their pointer values.
*/
static int hashcmpImmortalStrings(const void* vstrObj1, const void* vstrObj2)
{
return dvmHashcmpStrings((const void*) STRIP_IMMORTAL_BIT(vstrObj1),
(const void*) STRIP_IMMORTAL_BIT(vstrObj2));
}
static StringObject* lookupInternedString(StringObject* strObj, bool immortal)
{
StringObject* found;
u4 hash;
assert(strObj != NULL);
hash = dvmComputeStringHash(strObj);
if (false) {
char* debugStr = dvmCreateCstrFromString(strObj);
LOGV("+++ dvmLookupInternedString searching for '%s'\n", debugStr);
free(debugStr);
}
if (immortal) {
strObj = (StringObject*) SET_IMMORTAL_BIT(strObj);
}
dvmHashTableLock(gDvm.internedStrings);
found = (StringObject*) dvmHashTableLookup(gDvm.internedStrings,
hash, strObj, hashcmpImmortalStrings, true);
if (immortal && !IS_IMMORTAL(found)) {
/* Make this entry immortal. We have to use the existing object
* because, as an interned string, it's not allowed to change.
*
* There's no way to get a pointer to the actual hash table entry,
* so the only way to modify the existing entry is to remove,
* modify, and re-add it.
*/
dvmHashTableRemove(gDvm.internedStrings, hash, found);
found = (StringObject*) SET_IMMORTAL_BIT(found);
found = (StringObject*) dvmHashTableLookup(gDvm.internedStrings,
hash, found, hashcmpImmortalStrings, true);
assert(IS_IMMORTAL(found));
}
dvmHashTableUnlock(gDvm.internedStrings);
//if (found == strObj)
// LOGVV("+++ added string\n");
return (StringObject*) STRIP_IMMORTAL_BIT(found);
}
/*
* Find an entry in the interned string list.
*
* If the string doesn't already exist, the StringObject is added to
* the list. Otherwise, the existing entry is returned.
*/
StringObject* dvmLookupInternedString(StringObject* strObj)
{
return lookupInternedString(strObj, false);
}
/*
* Same as dvmLookupInternedString(), but guarantees that the
* returned string is immortal.
*/
StringObject* dvmLookupImmortalInternedString(StringObject* strObj)
{
return lookupInternedString(strObj, true);
}
/*
* Mark all immortal interned string objects so that they don't
* get collected by the GC. Non-immortal strings may or may not
* get marked by other references.
*/
static int markStringObject(void* strObj, void* arg)
{
UNUSED_PARAMETER(arg);
if (IS_IMMORTAL(strObj)) {
dvmMarkObjectNonNull((Object*) STRIP_IMMORTAL_BIT(strObj));
}
return 0;
}
void dvmGcScanInternedStrings()
{
/* It's possible for a GC to happen before dvmStringInternStartup()
* is called.
*/
if (gDvm.internedStrings != NULL) {
dvmHashTableLock(gDvm.internedStrings);
dvmHashForeach(gDvm.internedStrings, markStringObject, NULL);
dvmHashTableUnlock(gDvm.internedStrings);
}
}
/*
* Called by the GC after all reachable objects have been
* marked. isUnmarkedObject is a function suitable for passing
* to dvmHashForeachRemove(); it must strip the low bits from
* its pointer argument to deal with the immortal bit, though.
*/
void dvmGcDetachDeadInternedStrings(int (*isUnmarkedObject)(void *))
{
/* It's possible for a GC to happen before dvmStringInternStartup()
* is called.
*/
if (gDvm.internedStrings != NULL) {
dvmHashTableLock(gDvm.internedStrings);
dvmHashForeachRemove(gDvm.internedStrings, isUnmarkedObject);
dvmHashTableUnlock(gDvm.internedStrings);
}
}