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)" : ""); } } }