/* Mark all objects referred to by the ClassObject.
*/
static void scanClassObject(const ClassObject *clazz, GcMarkContext *ctx)
{
LOGV_SCAN("---------> %s\n", clazz->name);
if (IS_CLASS_FLAG_SET(clazz, CLASS_ISARRAY)) {
/* We're an array; mark the class object of the contents
* of the array.
*
* Note that we won't necessarily reach the array's element
* class by scanning the array contents; the array may be
* zero-length, or may only contain null objects.
*/
markObjectNonNull((Object *)clazz->elementClass, ctx);
}
/* We scan these explicitly in case the only remaining
* reference to a particular class object is via a data
* object; we may not be guaranteed to reach all
* live class objects via a classloader.
*/
markObject((Object *)clazz->super, ctx); // may be NULL (java.lang.Object)
markObject(clazz->classLoader, ctx); // may be NULL
scanStaticFields(clazz, ctx);
markInterfaces(clazz, ctx);
}
/*
* Callback applied to root references. If the root location contains
* a white reference it is pushed on the mark stack and grayed.
*/
static void markObjectVisitor(void *addr, void *arg)
{
Object *obj;
assert(addr != NULL);
assert(arg != NULL);
obj = *(Object **)addr;
if (obj != NULL) {
markObjectNonNull(obj, arg, true);
}
}
/*
* Callback applied to root references during root remarking. Marks
* white objects and pushes them on the mark stack.
*/
static void rootReMarkObjectVisitor(void *addr, u4 thread, RootType type,
void *arg)
{
assert(addr != NULL);
assert(arg != NULL);
Object *obj = *(Object **)addr;
GcMarkContext *ctx = (GcMarkContext *)arg;
if (obj != NULL) {
markObjectNonNull(obj, ctx, true);
}
}
/* Mark all of a ClassObject's interfaces.
*/
static void markInterfaces(const ClassObject *clazz, GcMarkContext *ctx)
{
ClassObject **interfaces;
int interfaceCount;
int i;
/* Mark all interfaces.
*/
interfaces = clazz->interfaces;
interfaceCount = clazz->interfaceCount;
for (i = 0; i < interfaceCount; i++) {
markObjectNonNull((Object *)*interfaces, ctx);
interfaces++;
}
}
/* All objects for stronger reference levels have been
* marked before this is called.
*/
void dvmHeapHandleReferences(Object *refListHead, enum RefType refType)
{
Object *reference;
GcMarkContext *markContext = &gDvm.gcHeap->markContext;
const int offVmData = gDvm.offJavaLangRefReference_vmData;
const int offReferent = gDvm.offJavaLangRefReference_referent;
bool workRequired = false;
size_t numCleared = 0;
size_t numEnqueued = 0;
reference = refListHead;
while (reference != NULL) {
Object *next;
Object *referent;
/* Pull the interesting fields out of the Reference object.
*/
next = dvmGetFieldObject(reference, offVmData);
referent = dvmGetFieldObject(reference, offReferent);
//TODO: when handling REF_PHANTOM, unlink any references
// that fail this initial if(). We need to re-walk
// the list, and it would be nice to avoid the extra
// work.
if (referent != NULL && !isMarked(ptr2chunk(referent), markContext)) {
bool schedClear, schedEnqueue;
/* This is the strongest reference that refers to referent.
* Do the right thing.
*/
switch (refType) {
case REF_SOFT:
case REF_WEAK:
schedClear = clearReference(reference);
schedEnqueue = enqueueReference(reference);
break;
case REF_PHANTOM:
/* PhantomReferences are not cleared automatically.
* Until someone clears it (or the reference itself
* is collected), the referent must remain alive.
*
* It's necessary to fully mark the referent because
* it will still be present during the next GC, and
* all objects that it points to must be valid.
* (The referent will be marked outside of this loop,
* after handing all references of this strength, in
* case multiple references point to the same object.)
*/
schedClear = false;
/* A PhantomReference is only useful with a
* queue, but since it's possible to create one
* without a queue, we need to check.
*/
schedEnqueue = enqueueReference(reference);
break;
default:
assert(!"Bad reference type");
schedClear = false;
schedEnqueue = false;
break;
}
numCleared += schedClear ? 1 : 0;
numEnqueued += schedEnqueue ? 1 : 0;
if (schedClear || schedEnqueue) {
uintptr_t workBits;
/* Stuff the clear/enqueue bits in the bottom of
* the pointer. Assumes that objects are 8-byte
* aligned.
*
* Note that we are adding the *Reference* (which
* is by definition already marked at this point) to
* this list; we're not adding the referent (which
* has already been cleared).
*/
assert(((intptr_t)reference & 3) == 0);
assert(((WORKER_CLEAR | WORKER_ENQUEUE) & ~3) == 0);
workBits = (schedClear ? WORKER_CLEAR : 0) |
(schedEnqueue ? WORKER_ENQUEUE : 0);
if (!dvmHeapAddRefToLargeTable(
&gDvm.gcHeap->referenceOperations,
(Object *)((uintptr_t)reference | workBits)))
{
LOGE_HEAP("dvmMalloc(): no room for any more "
"reference operations\n");
dvmAbort();
}
workRequired = true;
}
if (refType != REF_PHANTOM) {
/* Let later GCs know not to reschedule this reference.
*/
dvmSetFieldObject(reference, offVmData,
SCHEDULED_REFERENCE_MAGIC);
} // else this is handled later for REF_PHANTOM
} // else there was a stronger reference to the referent.
reference = next;
}
#define refType2str(r) \
((r) == REF_SOFT ? "soft" : ( \
(r) == REF_WEAK ? "weak" : ( \
(r) == REF_PHANTOM ? "phantom" : "UNKNOWN" )))
LOGD_HEAP("dvmHeapHandleReferences(): cleared %zd, enqueued %zd %s references\n", numCleared, numEnqueued, refType2str(refType));
/* Walk though the reference list again, and mark any non-clear/marked
* referents. Only PhantomReferences can have non-clear referents
* at this point.
*/
if (refType == REF_PHANTOM) {
bool scanRequired = false;
HPROF_SET_GC_SCAN_STATE(HPROF_ROOT_REFERENCE_CLEANUP, 0);
reference = refListHead;
while (reference != NULL) {
Object *next;
Object *referent;
/* Pull the interesting fields out of the Reference object.
*/
next = dvmGetFieldObject(reference, offVmData);
referent = dvmGetFieldObject(reference, offReferent);
if (referent != NULL && !isMarked(ptr2chunk(referent), markContext)) {
markObjectNonNull(referent, markContext);
scanRequired = true;
/* Let later GCs know not to reschedule this reference.
*/
dvmSetFieldObject(reference, offVmData,
SCHEDULED_REFERENCE_MAGIC);
}
reference = next;
}
HPROF_CLEAR_GC_SCAN_STATE();
if (scanRequired) {
processMarkStack(markContext);
}
}
if (workRequired) {
dvmSignalHeapWorker(false);
}
}
/* Mark all objects that obj refers to.
*
* Called on every object in markList.
*/
static void scanObject(const Object *obj, GcMarkContext *ctx)
{
ClassObject *clazz;
assert(dvmIsValidObject(obj));
LOGV_SCAN("0x%08x %s\n", (uint)obj, obj->clazz->name);
#if WITH_HPROF
if (gDvm.gcHeap->hprofContext != NULL) {
hprofDumpHeapObject(gDvm.gcHeap->hprofContext, obj);
}
#endif
/* Get and mark the class object for this particular instance.
*/
clazz = obj->clazz;
if (clazz == NULL) {
/* This can happen if we catch an object between
* dvmMalloc() and DVM_OBJECT_INIT(). The object
* won't contain any references yet, so we can
* just skip it.
*/
return;
} else if (clazz == gDvm.unlinkedJavaLangClass) {
/* This class hasn't been linked yet. We're guaranteed
* that the object doesn't contain any references that
* aren't already tracked, so we can skip scanning it.
*
* NOTE: unlinkedJavaLangClass is not on the heap, so
* it's very important that we don't try marking it.
*/
return;
}
#if WITH_OBJECT_HEADERS
gMarkParent = obj;
if (ptr2chunk(obj)->scanGeneration == gGeneration) {
LOGE("object 0x%08x was already scanned this generation\n",
(uintptr_t)obj);
dvmAbort();
}
ptr2chunk(obj)->oldScanGeneration = ptr2chunk(obj)->scanGeneration;
ptr2chunk(obj)->scanGeneration = gGeneration;
ptr2chunk(obj)->scanCount++;
#endif
assert(dvmIsValidObject((Object *)clazz));
markObjectNonNull((Object *)clazz, ctx);
/* Mark any references in this object.
*/
if (IS_CLASS_FLAG_SET(clazz, CLASS_ISARRAY)) {
/* It's an array object.
*/
if (IS_CLASS_FLAG_SET(clazz, CLASS_ISOBJECTARRAY)) {
/* It's an array of object references.
*/
scanObjectArray((ArrayObject *)obj, ctx);
}
// else there's nothing else to scan
} else {
/* It's a DataObject-compatible object.
*/
scanInstanceFields((DataObject *)obj, clazz, ctx);
if (IS_CLASS_FLAG_SET(clazz, CLASS_ISREFERENCE)) {
GcHeap *gcHeap = gDvm.gcHeap;
Object *referent;
/* It's a subclass of java/lang/ref/Reference.
* The fields in this class have been arranged
* such that scanInstanceFields() did not actually
* mark the "referent" field; we need to handle
* it specially.
*
* If the referent already has a strong mark (isMarked(referent)),
* we don't care about its reference status.
*/
referent = dvmGetFieldObject(obj,
gDvm.offJavaLangRefReference_referent);
if (referent != NULL &&
!isMarked(ptr2chunk(referent), &gcHeap->markContext))
{
u4 refFlags;
if (gcHeap->markAllReferents) {
LOG_REF("Hard-marking a reference\n");
/* Don't bother with normal reference-following
* behavior, just mark the referent. This should
* only be used when following objects that just
* became scheduled for finalization.
*/
markObjectNonNull(referent, ctx);
goto skip_reference;
}
/* See if this reference was handled by a previous GC.
*/
if (dvmGetFieldObject(obj,
gDvm.offJavaLangRefReference_vmData) ==
SCHEDULED_REFERENCE_MAGIC)
{
LOG_REF("Skipping scheduled reference\n");
/* Don't reschedule it, but make sure that its
* referent doesn't get collected (in case it's
* a PhantomReference and wasn't cleared automatically).
*/
//TODO: Mark these after handling all new refs of
// this strength, in case the new refs refer
// to the same referent. Not a very common
// case, though.
markObjectNonNull(referent, ctx);
goto skip_reference;
}
/* Find out what kind of reference is pointing
* to referent.
*/
refFlags = GET_CLASS_FLAG_GROUP(clazz,
CLASS_ISREFERENCE |
CLASS_ISWEAKREFERENCE |
CLASS_ISPHANTOMREFERENCE);
/* We use the vmData field of Reference objects
* as a next pointer in a singly-linked list.
* That way, we don't need to allocate any memory
* while we're doing a GC.
*/
#define ADD_REF_TO_LIST(list, ref) \
do { \
Object *ARTL_ref_ = (/*de-const*/Object *)(ref); \
dvmSetFieldObject(ARTL_ref_, \
gDvm.offJavaLangRefReference_vmData, list); \
list = ARTL_ref_; \
} while (false)
/* At this stage, we just keep track of all of
* the live references that we've seen. Later,
* we'll walk through each of these lists and
* deal with the referents.
*/
if (refFlags == CLASS_ISREFERENCE) {
/* It's a soft reference. Depending on the state,
* we'll attempt to collect all of them, some of
* them, or none of them.
*/
if (gcHeap->softReferenceCollectionState ==
SR_COLLECT_NONE)
{
sr_collect_none:
markObjectNonNull(referent, ctx);
} else if (gcHeap->softReferenceCollectionState ==
SR_COLLECT_ALL)
{
sr_collect_all:
ADD_REF_TO_LIST(gcHeap->softReferences, obj);
} else {
/* We'll only try to collect half of the
* referents.
*/
if (gcHeap->softReferenceColor++ & 1) {
goto sr_collect_none;
}
goto sr_collect_all;
}
} else {
/* It's a weak or phantom reference.
* Clearing CLASS_ISREFERENCE will reveal which.
*/
refFlags &= ~CLASS_ISREFERENCE;
if (refFlags == CLASS_ISWEAKREFERENCE) {
ADD_REF_TO_LIST(gcHeap->weakReferences, obj);
} else if (refFlags == CLASS_ISPHANTOMREFERENCE) {
ADD_REF_TO_LIST(gcHeap->phantomReferences, obj);
} else {
assert(!"Unknown reference type");
}
}
#undef ADD_REF_TO_LIST
}
}
skip_reference:
/* If this is a class object, mark various other things that
* its internals point to.
*
* All class objects are instances of java.lang.Class,
* including the java.lang.Class class object.
*/
if (clazz == gDvm.classJavaLangClass) {
scanClassObject((ClassObject *)obj, ctx);
}
}
#if WITH_OBJECT_HEADERS
gMarkParent = NULL;
#endif
}
/* Find unreachable objects that need to be finalized,
* and schedule them for finalization.
*/
void dvmHeapScheduleFinalizations()
{
HeapRefTable newPendingRefs;
LargeHeapRefTable *finRefs = gDvm.gcHeap->finalizableRefs;
Object **ref;
Object **lastRef;
size_t totalPendCount;
GcMarkContext *markContext = &gDvm.gcHeap->markContext;
/*
* All reachable objects have been marked.
* Any unmarked finalizable objects need to be finalized.
*/
/* Create a table that the new pending refs will
* be added to.
*/
if (!dvmHeapInitHeapRefTable(&newPendingRefs, 128)) {
//TODO: mark all finalizable refs and hope that
// we can schedule them next time. Watch out,
// because we may be expecting to free up space
// by calling finalizers.
LOGE_GC("dvmHeapScheduleFinalizations(): no room for "
"pending finalizations\n");
dvmAbort();
}
/* Walk through finalizableRefs and move any unmarked references
* to the list of new pending refs.
*/
totalPendCount = 0;
while (finRefs != NULL) {
Object **gapRef;
size_t newPendCount = 0;
gapRef = ref = finRefs->refs.table;
lastRef = finRefs->refs.nextEntry;
while (ref < lastRef) {
DvmHeapChunk *hc;
hc = ptr2chunk(*ref);
if (!isMarked(hc, markContext)) {
if (!dvmHeapAddToHeapRefTable(&newPendingRefs, *ref)) {
//TODO: add the current table and allocate
// a new, smaller one.
LOGE_GC("dvmHeapScheduleFinalizations(): "
"no room for any more pending finalizations: %zd\n",
dvmHeapNumHeapRefTableEntries(&newPendingRefs));
dvmAbort();
}
newPendCount++;
} else {
/* This ref is marked, so will remain on finalizableRefs.
*/
if (newPendCount > 0) {
/* Copy it up to fill the holes.
*/
*gapRef++ = *ref;
} else {
/* No holes yet; don't bother copying.
*/
gapRef++;
}
}
ref++;
}
finRefs->refs.nextEntry = gapRef;
//TODO: if the table is empty when we're done, free it.
totalPendCount += newPendCount;
finRefs = finRefs->next;
}
LOGD_GC("dvmHeapScheduleFinalizations(): %zd finalizers triggered.\n",
totalPendCount);
if (totalPendCount == 0) {
/* No objects required finalization.
* Free the empty temporary table.
*/
dvmClearReferenceTable(&newPendingRefs);
return;
}
/* Add the new pending refs to the main list.
*/
if (!dvmHeapAddTableToLargeTable(&gDvm.gcHeap->pendingFinalizationRefs,
&newPendingRefs))
{
LOGE_GC("dvmHeapScheduleFinalizations(): can't insert new "
"pending finalizations\n");
dvmAbort();
}
//TODO: try compacting the main list with a memcpy loop
/* Mark the refs we just moved; we don't want them or their
* children to get swept yet.
*/
ref = newPendingRefs.table;
lastRef = newPendingRefs.nextEntry;
assert(ref < lastRef);
HPROF_SET_GC_SCAN_STATE(HPROF_ROOT_FINALIZING, 0);
while (ref < lastRef) {
markObjectNonNull(*ref, markContext);
ref++;
}
HPROF_CLEAR_GC_SCAN_STATE();
/* Set markAllReferents so that we don't collect referents whose
* only references are in final-reachable objects.
* TODO: eventually provide normal reference behavior by properly
* marking these references.
*/
gDvm.gcHeap->markAllReferents = true;
processMarkStack(markContext);
gDvm.gcHeap->markAllReferents = false;
dvmSignalHeapWorker(false);
}
/* If the object hasn't already been marked, mark it and
* schedule it to be scanned for references.
*
* obj may not be NULL. The macro dvmMarkObject() should
* be used in situations where a reference may be NULL.
*
* This function may only be called when marking the root
* set. When recursing, use the internal markObject().
*/
void dvmMarkObjectNonNull(const Object *obj)
{
assert(obj != NULL);
markObjectNonNull(obj, &gDvm.gcHeap->markContext, false);
}
/* Used to mark objects when recursing. Recursion is done by moving
* the finger across the bitmaps in address order and marking child
* objects. Any newly-marked objects whose addresses are lower than
* the finger won't be visited by the bitmap scan, so those objects
* need to be added to the mark stack.
*/
static void markObject(const Object *obj, GcMarkContext *ctx)
{
if (obj != NULL) {
markObjectNonNull(obj, ctx, true);
}
}