/*
* Unlink the reference list clearing references objects with unreachable
* referents. Cleared references registered to a reference queue are
* enqueued on the cleared list.
*/
static void clearAndEnqueueReferences(Env* env, Object** list, Object** cleared) {
// This code is a port of the clearWhiteReferences() function in Android's MarkSweep.cpp
assert(list != NULL);
assert(cleared != NULL);
while (*list != NULL) {
Object* ref = dequeuePendingReference(env, list);
Object* referent = rvmGetObjectInstanceFieldValue(env, ref, java_lang_ref_Reference_referent);
if (referent != NULL) {
clearReference(env, ref);
if (isEnqueuable(env, ref)) {
enqueueReference(env, ref, cleared);
}
}
}
assert(*list == NULL);
}
/*
* Enqueues finalizer references with unreachable referents. The
* referent is moved to the zombie field (which makes it reachable again),
* and the referent field is cleared.
*/
static void enqueueFinalizerReferences(Env* env, Object** list, Object** cleared) {
// This code is a port of the enqueueFinalizerReferences() function in Android's MarkSweep.cpp
assert(list != NULL);
while (*list != NULL) {
Object* ref = dequeuePendingReference(env, list);
Object* referent = rvmGetObjectInstanceFieldValue(env, ref, java_lang_ref_Reference_referent);
if (referent != NULL) {
/* If the referent is non-null the reference must queuable. */
assert(isEnqueuable(env, ref));
// Copy the referent to the zombie field
rvmSetObjectInstanceFieldValue(env, ref, java_lang_ref_FinalizerReference_zombie, referent);
// Clear the referent
clearReference(env, ref);
enqueueReference(env, ref, cleared);
}
}
assert(*list == NULL);
}
/* 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);
}
}
