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src/hotspot/share/gc/cms/concurrentMarkSweepGeneration.cpp
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rev 49289 : 8199735: Mark word updates need to use Access API
*** 1039,1049 ****
// Otherwise, copy the object. Here we must be careful to insert the
// klass pointer last, since this marks the block as an allocated object.
// Except with compressed oops it's the mark word.
HeapWord* old_ptr = (HeapWord*)old;
// Restore the mark word copied above.
! obj->set_mark(m);
assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
OrderAccess::storestore();
if (UseCompressedClassPointers) {
--- 1039,1049 ----
// Otherwise, copy the object. Here we must be careful to insert the
// klass pointer last, since this marks the block as an allocated object.
// Except with compressed oops it's the mark word.
HeapWord* old_ptr = (HeapWord*)old;
// Restore the mark word copied above.
! obj->set_mark_raw(m);
assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
OrderAccess::storestore();
if (UseCompressedClassPointers) {
*** 7806,7817 ****
size_t i = num;
oop cur = _overflow_list;
const markOop proto = markOopDesc::prototype();
NOT_PRODUCT(ssize_t n = 0;)
for (oop next; i > 0 && cur != NULL; cur = next, i--) {
! next = oop(cur->mark());
! cur->set_mark(proto); // until proven otherwise
assert(oopDesc::is_oop(cur), "Should be an oop");
bool res = stack->push(cur);
assert(res, "Bit off more than can chew?");
NOT_PRODUCT(n++;)
}
--- 7806,7817 ----
size_t i = num;
oop cur = _overflow_list;
const markOop proto = markOopDesc::prototype();
NOT_PRODUCT(ssize_t n = 0;)
for (oop next; i > 0 && cur != NULL; cur = next, i--) {
! next = oop(cur->mark_raw());
! cur->set_mark_raw(proto); // until proven otherwise
assert(oopDesc::is_oop(cur), "Should be an oop");
bool res = stack->push(cur);
assert(res, "Bit off more than can chew?");
NOT_PRODUCT(n++;)
}
*** 7890,7913 ****
}
assert(prefix != NULL && prefix != BUSY, "Error");
size_t i = num;
oop cur = prefix;
// Walk down the first "num" objects, unless we reach the end.
! for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
! if (cur->mark() == NULL) {
// We have "num" or fewer elements in the list, so there
// is nothing to return to the global list.
// Write back the NULL in lieu of the BUSY we wrote
// above, if it is still the same value.
if (_overflow_list == BUSY) {
Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
}
} else {
// Chop off the suffix and return it to the global list.
! assert(cur->mark() != BUSY, "Error");
! oop suffix_head = cur->mark(); // suffix will be put back on global list
! cur->set_mark(NULL); // break off suffix
// It's possible that the list is still in the empty(busy) state
// we left it in a short while ago; in that case we may be
// able to place back the suffix without incurring the cost
// of a walk down the list.
oop observed_overflow_list = _overflow_list;
--- 7890,7913 ----
}
assert(prefix != NULL && prefix != BUSY, "Error");
size_t i = num;
oop cur = prefix;
// Walk down the first "num" objects, unless we reach the end.
! for (; i > 1 && cur->mark_raw() != NULL; cur = oop(cur->mark_raw()), i--);
! if (cur->mark_raw() == NULL) {
// We have "num" or fewer elements in the list, so there
// is nothing to return to the global list.
// Write back the NULL in lieu of the BUSY we wrote
// above, if it is still the same value.
if (_overflow_list == BUSY) {
Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
}
} else {
// Chop off the suffix and return it to the global list.
! assert(cur->mark_raw() != BUSY, "Error");
! oop suffix_head = cur->mark_raw(); // suffix will be put back on global list
! cur->set_mark_raw(NULL); // break off suffix
// It's possible that the list is still in the empty(busy) state
// we left it in a short while ago; in that case we may be
// able to place back the suffix without incurring the cost
// of a walk down the list.
oop observed_overflow_list = _overflow_list;
*** 7923,7944 ****
}
if (!attached) {
// Too bad, someone else sneaked in (at least) an element; we'll need
// to do a splice. Find tail of suffix so we can prepend suffix to global
// list.
! for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
oop suffix_tail = cur;
! assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
"Tautology");
observed_overflow_list = _overflow_list;
do {
cur_overflow_list = observed_overflow_list;
if (cur_overflow_list != BUSY) {
// Do the splice ...
! suffix_tail->set_mark(markOop(cur_overflow_list));
} else { // cur_overflow_list == BUSY
! suffix_tail->set_mark(NULL);
}
// ... and try to place spliced list back on overflow_list ...
observed_overflow_list =
Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
} while (cur_overflow_list != observed_overflow_list);
--- 7923,7944 ----
}
if (!attached) {
// Too bad, someone else sneaked in (at least) an element; we'll need
// to do a splice. Find tail of suffix so we can prepend suffix to global
// list.
! for (cur = suffix_head; cur->mark_raw() != NULL; cur = (oop)(cur->mark_raw()));
oop suffix_tail = cur;
! assert(suffix_tail != NULL && suffix_tail->mark_raw() == NULL,
"Tautology");
observed_overflow_list = _overflow_list;
do {
cur_overflow_list = observed_overflow_list;
if (cur_overflow_list != BUSY) {
// Do the splice ...
! suffix_tail->set_mark_raw(markOop(cur_overflow_list));
} else { // cur_overflow_list == BUSY
! suffix_tail->set_mark_raw(NULL);
}
// ... and try to place spliced list back on overflow_list ...
observed_overflow_list =
Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
} while (cur_overflow_list != observed_overflow_list);
*** 7950,7961 ****
assert(prefix != NULL, "control point invariant");
const markOop proto = markOopDesc::prototype();
oop next;
NOT_PRODUCT(ssize_t n = 0;)
for (cur = prefix; cur != NULL; cur = next) {
! next = oop(cur->mark());
! cur->set_mark(proto); // until proven otherwise
assert(oopDesc::is_oop(cur), "Should be an oop");
bool res = work_q->push(cur);
assert(res, "Bit off more than we can chew?");
NOT_PRODUCT(n++;)
}
--- 7950,7961 ----
assert(prefix != NULL, "control point invariant");
const markOop proto = markOopDesc::prototype();
oop next;
NOT_PRODUCT(ssize_t n = 0;)
for (cur = prefix; cur != NULL; cur = next) {
! next = oop(cur->mark_raw());
! cur->set_mark_raw(proto); // until proven otherwise
assert(oopDesc::is_oop(cur), "Should be an oop");
bool res = work_q->push(cur);
assert(res, "Bit off more than we can chew?");
NOT_PRODUCT(n++;)
}
*** 7969,7979 ****
// Single-threaded
void CMSCollector::push_on_overflow_list(oop p) {
NOT_PRODUCT(_num_par_pushes++;)
assert(oopDesc::is_oop(p), "Not an oop");
preserve_mark_if_necessary(p);
! p->set_mark((markOop)_overflow_list);
_overflow_list = p;
}
// Multi-threaded; use CAS to prepend to overflow list
void CMSCollector::par_push_on_overflow_list(oop p) {
--- 7969,7979 ----
// Single-threaded
void CMSCollector::push_on_overflow_list(oop p) {
NOT_PRODUCT(_num_par_pushes++;)
assert(oopDesc::is_oop(p), "Not an oop");
preserve_mark_if_necessary(p);
! p->set_mark_raw((markOop)_overflow_list);
_overflow_list = p;
}
// Multi-threaded; use CAS to prepend to overflow list
void CMSCollector::par_push_on_overflow_list(oop p) {
*** 7983,7995 ****
oop observed_overflow_list = _overflow_list;
oop cur_overflow_list;
do {
cur_overflow_list = observed_overflow_list;
if (cur_overflow_list != BUSY) {
! p->set_mark(markOop(cur_overflow_list));
} else {
! p->set_mark(NULL);
}
observed_overflow_list =
Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list);
} while (cur_overflow_list != observed_overflow_list);
}
--- 7983,7995 ----
oop observed_overflow_list = _overflow_list;
oop cur_overflow_list;
do {
cur_overflow_list = observed_overflow_list;
if (cur_overflow_list != BUSY) {
! p->set_mark_raw(markOop(cur_overflow_list));
} else {
! p->set_mark_raw(NULL);
}
observed_overflow_list =
Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list);
} while (cur_overflow_list != observed_overflow_list);
}
*** 8010,8042 ****
// failures where possible, thus, incrementally hardening the VM
// in such low resource situations.
void CMSCollector::preserve_mark_work(oop p, markOop m) {
_preserved_oop_stack.push(p);
_preserved_mark_stack.push(m);
! assert(m == p->mark(), "Mark word changed");
assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
"bijection");
}
// Single threaded
void CMSCollector::preserve_mark_if_necessary(oop p) {
! markOop m = p->mark();
if (m->must_be_preserved(p)) {
preserve_mark_work(p, m);
}
}
void CMSCollector::par_preserve_mark_if_necessary(oop p) {
! markOop m = p->mark();
if (m->must_be_preserved(p)) {
MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
// Even though we read the mark word without holding
// the lock, we are assured that it will not change
// because we "own" this oop, so no other thread can
// be trying to push it on the overflow list; see
// the assertion in preserve_mark_work() that checks
! // that m == p->mark().
preserve_mark_work(p, m);
}
}
// We should be able to do this multi-threaded,
--- 8010,8042 ----
// failures where possible, thus, incrementally hardening the VM
// in such low resource situations.
void CMSCollector::preserve_mark_work(oop p, markOop m) {
_preserved_oop_stack.push(p);
_preserved_mark_stack.push(m);
! assert(m == p->mark_raw(), "Mark word changed");
assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
"bijection");
}
// Single threaded
void CMSCollector::preserve_mark_if_necessary(oop p) {
! markOop m = p->mark_raw();
if (m->must_be_preserved(p)) {
preserve_mark_work(p, m);
}
}
void CMSCollector::par_preserve_mark_if_necessary(oop p) {
! markOop m = p->mark_raw();
if (m->must_be_preserved(p)) {
MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
// Even though we read the mark word without holding
// the lock, we are assured that it will not change
// because we "own" this oop, so no other thread can
// be trying to push it on the overflow list; see
// the assertion in preserve_mark_work() that checks
! // that m == p->mark_raw().
preserve_mark_work(p, m);
}
}
// We should be able to do this multi-threaded,
*** 8065,8078 ****
while (!_preserved_oop_stack.is_empty()) {
oop p = _preserved_oop_stack.pop();
assert(oopDesc::is_oop(p), "Should be an oop");
assert(_span.contains(p), "oop should be in _span");
! assert(p->mark() == markOopDesc::prototype(),
"Set when taken from overflow list");
markOop m = _preserved_mark_stack.pop();
! p->set_mark(m);
}
assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
"stacks were cleared above");
}
--- 8065,8078 ----
while (!_preserved_oop_stack.is_empty()) {
oop p = _preserved_oop_stack.pop();
assert(oopDesc::is_oop(p), "Should be an oop");
assert(_span.contains(p), "oop should be in _span");
! assert(p->mark_raw() == markOopDesc::prototype(),
"Set when taken from overflow list");
markOop m = _preserved_mark_stack.pop();
! p->set_mark_raw(m);
}
assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
"stacks were cleared above");
}
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