HeapWord* GenCollectorPolicy::expand_heap_and_allocate(size_t size,
bool is_tlab) {
GenCollectedHeap *gch = GenCollectedHeap::heap();
HeapWord* result = NULL;
Generation *old = gch->old_gen();
if (old->should_allocate(size, is_tlab)) {
result = old->expand_and_allocate(size, is_tlab);
}
if (result == NULL) {
Generation *young = gch->young_gen();
if (young->should_allocate(size, is_tlab)) {
result = young->expand_and_allocate(size, is_tlab);
}
}
assert(result == NULL || gch->is_in_reserved(result), "result not in heap");
return result;
}
HeapWord* GenCollectorPolicy::expand_heap_and_allocate(size_t size,
bool is_tlab) {
GenCollectedHeap *gch = GenCollectedHeap::heap();
HeapWord* result = NULL;
for (int i = number_of_generations() - 1; i >= 0 && result == NULL; i--) {
Generation *gen = gch->get_gen(i);
if (gen->should_allocate(size, is_tlab)) {
result = gen->expand_and_allocate(size, is_tlab);
}
}
assert(result == NULL || gch->is_in_reserved(result), "result not in heap");
return result;
}
HeapWord* TwoGenerationCollectorPolicy::satisfy_failed_allocation(size_t size,
bool is_large_noref,
bool is_tlab,
bool* notify_ref_lock) {
GenCollectedHeap *gch = GenCollectedHeap::heap();
GCCauseSetter x(gch, GCCause::_allocation_failure);
HeapWord* result = NULL;
// The gc_prologues have not executed yet. The value
// for incremental_collection_will_fail() is the remanent
// of the last collection.
if (!gch->incremental_collection_will_fail()) {
// Do an incremental collection.
gch->do_collection(false /* full */,
false /* clear_all_soft_refs */,
size /* size */,
is_large_noref /* is_large_noref */,
is_tlab /* is_tlab */,
number_of_generations() - 1 /* max_level */,
notify_ref_lock /* notify_ref_lock */);
} else {
// The incremental_collection_will_fail flag is set if the
// next incremental collection will not succeed (e.g., the
// DefNewGeneration didn't think it had space to promote all
// its objects). However, that last incremental collection
// continued, allowing all older generations to collect (and
// perhaps change the state of the flag).
//
// If we reach here, we know that an incremental collection of
// all generations left us in the state where incremental collections
// will fail, so we just try allocating the requested space.
// If the allocation fails everywhere, force a full collection.
// We're probably very close to being out of memory, so forcing many
// collections now probably won't help.
if (PrintGC && Verbose) {
gclog_or_tty->print_cr("TwoGenerationCollectorPolicy::satisfy_failed_allocation:"
" attempting allocation anywhere before full collection");
}
result = gch->attempt_allocation(size,
is_large_noref,
is_tlab,
false /* first_only */);
if (result != NULL) {
assert(gch->is_in(result), "result not in heap");
return result;
}
// Allocation request hasn't yet been met; try a full collection.
gch->do_collection(true /* full */,
false /* clear_all_soft_refs */,
size /* size */,
is_large_noref /* is_large_noref */,
is_tlab /* is_tlab */,
number_of_generations() - 1 /* max_level */,
notify_ref_lock /* notify_ref_lock */);
}
result = gch->attempt_allocation(size, is_large_noref, is_tlab, false /*first_only*/);
if (result != NULL) {
assert(gch->is_in(result), "result not in heap");
return result;
}
// OK, collection failed, try expansion.
for (int i = number_of_generations() - 1 ; i>= 0; i--) {
Generation *gen = gch->get_gen(i);
if (gen->should_allocate(size, is_large_noref, is_tlab)) {
result = gen->expand_and_allocate(size, is_large_noref, is_tlab);
if (result != NULL) {
assert(gch->is_in(result), "result not in heap");
return result;
}
}
}
// If we reach this point, we're really out of memory. Try every trick
// we can to reclaim memory. Force collection of soft references. Force
// a complete compaction of the heap. Any additional methods for finding
// free memory should be here, especially if they are expensive. If this
// attempt fails, an OOM exception will be thrown.
{
IntFlagSetting flag_change(MarkSweepAlwaysCompactCount, 1); // Make sure the heap is fully compacted
gch->do_collection(true /* full */,
true /* clear_all_soft_refs */,
size /* size */,
is_large_noref /* is_large_noref */,
is_tlab /* is_tlab */,
number_of_generations() - 1 /* max_level */,
notify_ref_lock /* notify_ref_lock */);
}
result = gch->attempt_allocation(size, is_large_noref, is_tlab, false /* first_only */);
if (result != NULL) {
assert(gch->is_in(result), "result not in heap");
return result;
}
// What else? We might try synchronous finalization later. If the total
// space available is large enough for the allocation, then a more
// complete compaction phase than we've tried so far might be
// appropriate.
return NULL;
}
HeapWord* GenCollectorPolicy::mem_allocate_work(size_t size,
bool is_tlab,
bool* gc_overhead_limit_was_exceeded) {
GenCollectedHeap *gch = GenCollectedHeap::heap();
debug_only(gch->check_for_valid_allocation_state());
assert(gch->no_gc_in_progress(), "Allocation during gc not allowed");
// In general gc_overhead_limit_was_exceeded should be false so
// set it so here and reset it to true only if the gc time
// limit is being exceeded as checked below.
*gc_overhead_limit_was_exceeded = false;
HeapWord* result = NULL;
// Loop until the allocation is satisfied, or unsatisfied after GC.
for (uint try_count = 1, gclocker_stalled_count = 0; /* return or throw */; try_count += 1) {
HandleMark hm; // Discard any handles allocated in each iteration.
// First allocation attempt is lock-free.
Generation *young = gch->young_gen();
assert(young->supports_inline_contig_alloc(),
"Otherwise, must do alloc within heap lock");
if (young->should_allocate(size, is_tlab)) {
result = young->par_allocate(size, is_tlab);
if (result != NULL) {
assert(gch->is_in_reserved(result), "result not in heap");
return result;
}
}
uint gc_count_before; // Read inside the Heap_lock locked region.
{
MutexLocker ml(Heap_lock);
log_trace(gc, alloc)("GenCollectorPolicy::mem_allocate_work: attempting locked slow path allocation");
// Note that only large objects get a shot at being
// allocated in later generations.
bool first_only = ! should_try_older_generation_allocation(size);
result = gch->attempt_allocation(size, is_tlab, first_only);
if (result != NULL) {
assert(gch->is_in_reserved(result), "result not in heap");
return result;
}
if (GCLocker::is_active_and_needs_gc()) {
if (is_tlab) {
return NULL; // Caller will retry allocating individual object.
}
if (!gch->is_maximal_no_gc()) {
// Try and expand heap to satisfy request.
result = expand_heap_and_allocate(size, is_tlab);
// Result could be null if we are out of space.
if (result != NULL) {
return result;
}
}
if (gclocker_stalled_count > GCLockerRetryAllocationCount) {
return NULL; // We didn't get to do a GC and we didn't get any memory.
}
// If this thread is not in a jni critical section, we stall
// the requestor until the critical section has cleared and
// GC allowed. When the critical section clears, a GC is
// initiated by the last thread exiting the critical section; so
// we retry the allocation sequence from the beginning of the loop,
// rather than causing more, now probably unnecessary, GC attempts.
JavaThread* jthr = JavaThread::current();
if (!jthr->in_critical()) {
MutexUnlocker mul(Heap_lock);
// Wait for JNI critical section to be exited
GCLocker::stall_until_clear();
gclocker_stalled_count += 1;
continue;
} else {
if (CheckJNICalls) {
fatal("Possible deadlock due to allocating while"
" in jni critical section");
}
return NULL;
}
}
// Read the gc count while the heap lock is held.
gc_count_before = gch->total_collections();
}
VM_GenCollectForAllocation op(size, is_tlab, gc_count_before);
VMThread::execute(&op);
if (op.prologue_succeeded()) {
result = op.result();
if (op.gc_locked()) {
assert(result == NULL, "must be NULL if gc_locked() is true");
continue; // Retry and/or stall as necessary.
}
// Allocation has failed and a collection
// has been done. If the gc time limit was exceeded the
// this time, return NULL so that an out-of-memory
// will be thrown. Clear gc_overhead_limit_exceeded
// so that the overhead exceeded does not persist.
const bool limit_exceeded = size_policy()->gc_overhead_limit_exceeded();
const bool softrefs_clear = all_soft_refs_clear();
if (limit_exceeded && softrefs_clear) {
*gc_overhead_limit_was_exceeded = true;
size_policy()->set_gc_overhead_limit_exceeded(false);
if (op.result() != NULL) {
CollectedHeap::fill_with_object(op.result(), size);
}
return NULL;
}
assert(result == NULL || gch->is_in_reserved(result),
"result not in heap");
return result;
}
// Give a warning if we seem to be looping forever.
if ((QueuedAllocationWarningCount > 0) &&
(try_count % QueuedAllocationWarningCount == 0)) {
log_warning(gc, ergo)("GenCollectorPolicy::mem_allocate_work retries %d times,"
" size=" SIZE_FORMAT " %s", try_count, size, is_tlab ? "(TLAB)" : "");
}
}
}
