HeapWord* ConcEdenSpace::par_allocate(size_t size)
{
do {
// The invariant is top() should be read before end() because
// top() can't be greater than end(), so if an update of _soft_end
// occurs between 'end_val = end();' and 'top_val = top();' top()
// also can grow up to the new end() and the condition
// 'top_val > end_val' is true. To ensure the loading order
// OrderAccess::loadload() is required after top() read.
HeapWord* obj = top();
OrderAccess::loadload();
if (pointer_delta(*soft_end_addr(), obj) >= size) {
HeapWord* new_top = obj + size;
HeapWord* result = (HeapWord*)Atomic::cmpxchg_ptr(new_top, top_addr(), obj);
// result can be one of two:
// the old top value: the exchange succeeded
// otherwise: the new value of the top is returned.
if (result == obj) {
assert(is_aligned(obj) && is_aligned(new_top), "checking alignment");
return obj;
}
} else {
return NULL;
}
} while (true);
}
// This version is lock-free.
inline HeapWord* ContiguousSpace::par_allocate_impl(size_t size,
HeapWord* const end_value) {
do {
HeapWord* obj = top();
if (pointer_delta(end_value, obj) >= size) {
HeapWord* new_top = obj + size;
HeapWord* result = (HeapWord*)Atomic::cmpxchg_ptr(new_top, top_addr(), obj);
// result can be one of two:
// the old top value: the exchange succeeded
// otherwise: the new value of the top is returned.
if (result == obj) {
return obj;
}
} else {
return NULL;
}
} while (true);
}
