void G1AllocRegion::setup(G1CollectedHeap* g1h, HeapRegion* dummy_region) {
assert(_dummy_region == NULL, "should be set once");
assert(dummy_region != NULL, "pre-condition");
assert(dummy_region->free() == 0, "pre-condition");
// Make sure that any allocation attempt on this region will fail
// and will not trigger any asserts.
assert(allocate(dummy_region, 1, false) == NULL, "should fail");
assert(par_allocate(dummy_region, 1, false) == NULL, "should fail");
assert(allocate(dummy_region, 1, true) == NULL, "should fail");
assert(par_allocate(dummy_region, 1, true) == NULL, "should fail");
_g1h = g1h;
_dummy_region = dummy_region;
}
/**
* 并发分配
*/
inline HeapWord* G1AllocRegion::attempt_allocation(size_t word_size,
bool bot_updates) {
assert(bot_updates == _bot_updates, ar_ext_msg(this, "pre-condition"));
HeapRegion* alloc_region = _alloc_region;
assert(alloc_region != NULL, ar_ext_msg(this, "not initialized properly"));
HeapWord* result = par_allocate(alloc_region, word_size, bot_updates);
if (result != NULL) {
trace("alloc", word_size, result);
return result;
}
trace("alloc failed", word_size);
return NULL;
}
void G1AllocRegion::fill_up_remaining_space(HeapRegion* alloc_region,
bool bot_updates) {
assert(alloc_region != NULL && alloc_region != _dummy_region,
"pre-condition");
// Other threads might still be trying to allocate using a CAS out
// of the region we are trying to retire, as they can do so without
// holding the lock. So, we first have to make sure that noone else
// can allocate out of it by doing a maximal allocation. Even if our
// CAS attempt fails a few times, we'll succeed sooner or later
// given that failed CAS attempts mean that the region is getting
// closed to being full.
size_t free_word_size = alloc_region->free() / HeapWordSize;
// This is the minimum free chunk we can turn into a dummy
// object. If the free space falls below this, then noone can
// allocate in this region anyway (all allocation requests will be
// of a size larger than this) so we won't have to perform the dummy
// allocation.
size_t min_word_size_to_fill = CollectedHeap::min_fill_size();
while (free_word_size >= min_word_size_to_fill) {
HeapWord* dummy = par_allocate(alloc_region, free_word_size, bot_updates);
if (dummy != NULL) {
// If the allocation was successful we should fill in the space.
CollectedHeap::fill_with_object(dummy, free_word_size);
alloc_region->set_pre_dummy_top(dummy);
break;
}
free_word_size = alloc_region->free() / HeapWordSize;
// It's also possible that someone else beats us to the
// allocation and they fill up the region. In that case, we can
// just get out of the loop.
}
assert(alloc_region->free() / HeapWordSize < min_word_size_to_fill,
"post-condition");
}
