# HG changeset patch # User johnc # Date 1360084385 28800 # Node ID f90b9bceb8e56906ac38bc3396ab018b6c1972b0 # Parent 84304a77c4e3ab6b53724aeb0eb785b12dc4a9e9 8005032: G1: Cleanup serial reference processing closures in concurrent marking Summary: Reuse the parallel reference processing oop closures during serial reference processing. Reviewed-by: brutisso diff -r 84304a77c4e3 -r f90b9bceb8e5 src/share/vm/gc_implementation/g1/concurrentMark.cpp --- a/src/share/vm/gc_implementation/g1/concurrentMark.cpp Mon Feb 04 19:40:27 2013 -0800 +++ b/src/share/vm/gc_implementation/g1/concurrentMark.cpp Tue Feb 05 09:13:05 2013 -0800 @@ -2167,7 +2167,8 @@ assert(tmp_free_list.is_empty(), "post-condition"); } -// Support closures for reference procssing in G1 +// Supporting Object and Oop closures for reference discovery +// and processing in during marking bool G1CMIsAliveClosure::do_object_b(oop obj) { HeapWord* addr = (HeapWord*)obj; @@ -2175,73 +2176,26 @@ (!_g1->is_in_g1_reserved(addr) || !_g1->is_obj_ill(obj)); } -class G1CMKeepAliveClosure: public ExtendedOopClosure { - G1CollectedHeap* _g1; - ConcurrentMark* _cm; - public: - G1CMKeepAliveClosure(G1CollectedHeap* g1, ConcurrentMark* cm) : - _g1(g1), _cm(cm) { - assert(Thread::current()->is_VM_thread(), "otherwise fix worker id"); - } - - virtual void do_oop(narrowOop* p) { do_oop_work(p); } - virtual void do_oop( oop* p) { do_oop_work(p); } - - template void do_oop_work(T* p) { - oop obj = oopDesc::load_decode_heap_oop(p); - HeapWord* addr = (HeapWord*)obj; - - if (_cm->verbose_high()) { - gclog_or_tty->print_cr("\t[0] we're looking at location " - "*"PTR_FORMAT" = "PTR_FORMAT, - p, (void*) obj); - } - - if (_g1->is_in_g1_reserved(addr) && _g1->is_obj_ill(obj)) { - _cm->mark_and_count(obj); - _cm->mark_stack_push(obj); - } - } -}; - -class G1CMDrainMarkingStackClosure: public VoidClosure { - ConcurrentMark* _cm; - CMMarkStack* _markStack; - G1CMKeepAliveClosure* _oopClosure; - public: - G1CMDrainMarkingStackClosure(ConcurrentMark* cm, CMMarkStack* markStack, - G1CMKeepAliveClosure* oopClosure) : - _cm(cm), - _markStack(markStack), - _oopClosure(oopClosure) { } - - void do_void() { - _markStack->drain(_oopClosure, _cm->nextMarkBitMap(), false); - } -}; - -// 'Keep Alive' closure used by parallel reference processing. -// An instance of this closure is used in the parallel reference processing -// code rather than an instance of G1CMKeepAliveClosure. We could have used -// the G1CMKeepAliveClosure as it is MT-safe. Also reference objects are -// placed on to discovered ref lists once so we can mark and push with no -// need to check whether the object has already been marked. Using the -// G1CMKeepAliveClosure would mean, however, having all the worker threads -// operating on the global mark stack. This means that an individual -// worker would be doing lock-free pushes while it processes its own -// discovered ref list followed by drain call. If the discovered ref lists -// are unbalanced then this could cause interference with the other -// workers. Using a CMTask (and its embedded local data structures) -// avoids that potential interference. -class G1CMParKeepAliveAndDrainClosure: public OopClosure { +// 'Keep Alive' oop closure used by both serial parallel reference processing. +// Uses the CMTask associated with a worker thread (for serial reference +// processing the CMTask for worker 0 is used) to preserve (mark) and +// trace referent objects. +// +// Using the CMTask and embedded local queues avoids having the worker +// threads operating on the global mark stack. This reduces the risk +// of overflowing the stack - which we would rather avoid at this late +// state. Also using the tasks' local queues removes the potential +// of the workers interfering with each other that could occur if +// operating on the global stack. + +class G1CMKeepAliveAndDrainClosure: public OopClosure { ConcurrentMark* _cm; CMTask* _task; int _ref_counter_limit; int _ref_counter; public: - G1CMParKeepAliveAndDrainClosure(ConcurrentMark* cm, CMTask* task) : - _cm(cm), _task(task), - _ref_counter_limit(G1RefProcDrainInterval) { + G1CMKeepAliveAndDrainClosure(ConcurrentMark* cm, CMTask* task) : + _cm(cm), _task(task), _ref_counter_limit(G1RefProcDrainInterval) { assert(_ref_counter_limit > 0, "sanity"); _ref_counter = _ref_counter_limit; } @@ -2262,18 +2216,22 @@ _ref_counter--; if (_ref_counter == 0) { - // We have dealt with _ref_counter_limit references, pushing them and objects - // reachable from them on to the local stack (and possibly the global stack). - // Call do_marking_step() to process these entries. We call the routine in a - // loop, which we'll exit if there's nothing more to do (i.e. we're done - // with the entries that we've pushed as a result of the deal_with_reference - // calls above) or we overflow. - // Note: CMTask::do_marking_step() can set the CMTask::has_aborted() flag - // while there may still be some work to do. (See the comment at the - // beginning of CMTask::do_marking_step() for those conditions - one of which - // is reaching the specified time target.) It is only when - // CMTask::do_marking_step() returns without setting the has_aborted() flag - // that the marking has completed. + // We have dealt with _ref_counter_limit references, pushing them + // and objects reachable from them on to the local stack (and + // possibly the global stack). Call CMTask::do_marking_step() to + // process these entries. + // + // We call CMTask::do_marking_step() in a loop, which we'll exit if + // there's nothing more to do (i.e. we're done with the entries that + // were pushed as a result of the CMTask::deal_with_reference() calls + // above) or we overflow. + // + // Note: CMTask::do_marking_step() can set the CMTask::has_aborted() + // flag while there may still be some work to do. (See the comment at + // the beginning of CMTask::do_marking_step() for those conditions - + // one of which is reaching the specified time target.) It is only + // when CMTask::do_marking_step() returns without setting the + // has_aborted() flag that the marking step has completed. do { double mark_step_duration_ms = G1ConcMarkStepDurationMillis; _task->do_marking_step(mark_step_duration_ms, @@ -2290,36 +2248,59 @@ } }; -class G1CMParDrainMarkingStackClosure: public VoidClosure { +// 'Drain' oop closure used by both serial and parallel reference processing. +// Uses the CMTask associated with a given worker thread (for serial +// reference processing the CMtask for worker 0 is used). Calls the +// do_marking_step routine, with an unbelievably large timeout value, +// to drain the marking data structures of the remaining entries +// added by the 'keep alive' oop closure above. + +class G1CMDrainMarkingStackClosure: public VoidClosure { ConcurrentMark* _cm; - CMTask* _task; + CMTask* _task; + bool _do_stealing; + bool _do_termination; public: - G1CMParDrainMarkingStackClosure(ConcurrentMark* cm, CMTask* task) : - _cm(cm), _task(task) { } + G1CMDrainMarkingStackClosure(ConcurrentMark* cm, CMTask* task, bool is_par) : + _cm(cm), _task(task) { + assert(is_par || _task->worker_id() == 0, + "Only task for worker 0 should be used if ref processing is single threaded"); + // We only allow stealing and only enter the termination protocol + // in CMTask::do_marking_step() if this closure is being instantiated + // for parallel reference processing. + _do_stealing = _do_termination = is_par; + } void do_void() { do { if (_cm->verbose_high()) { - gclog_or_tty->print_cr("\t[%u] Drain: Calling do marking_step", - _task->worker_id()); + gclog_or_tty->print_cr("\t[%u] Drain: Calling do_marking_step - " + "stealing: %s, termination: %s", + _task->worker_id(), + BOOL_TO_STR(_do_stealing), + BOOL_TO_STR(_do_termination)); } - // We call CMTask::do_marking_step() to completely drain the local and - // global marking stacks. The routine is called in a loop, which we'll - // exit if there's nothing more to do (i.e. we'completely drained the - // entries that were pushed as a result of applying the - // G1CMParKeepAliveAndDrainClosure to the entries on the discovered ref - // lists above) or we overflow the global marking stack. - // Note: CMTask::do_marking_step() can set the CMTask::has_aborted() flag - // while there may still be some work to do. (See the comment at the - // beginning of CMTask::do_marking_step() for those conditions - one of which - // is reaching the specified time target.) It is only when - // CMTask::do_marking_step() returns without setting the has_aborted() flag - // that the marking has completed. + // We call CMTask::do_marking_step() to completely drain the local + // and global marking stacks of entries pushed by the 'keep alive' + // oop closure (an instance of G1CMKeepAliveAndDrainClosure above). + // + // CMTask::do_marking_step() is called in a loop, which we'll exit + // if there's nothing more to do (i.e. we'completely drained the + // entries that were pushed as a a result of applying the 'keep alive' + // closure to the entries on the discovered ref lists) or we overflow + // the global marking stack. + // + // Note: CMTask::do_marking_step() can set the CMTask::has_aborted() + // flag while there may still be some work to do. (See the comment at + // the beginning of CMTask::do_marking_step() for those conditions - + // one of which is reaching the specified time target.) It is only + // when CMTask::do_marking_step() returns without setting the + // has_aborted() flag that the marking step has completed. _task->do_marking_step(1000000000.0 /* something very large */, - true /* do_stealing */, - true /* do_termination */); + _do_stealing, + _do_termination); } while (_task->has_aborted() && !_cm->has_overflown()); } }; @@ -2352,19 +2333,23 @@ ProcessTask& _proc_task; G1CollectedHeap* _g1h; ConcurrentMark* _cm; + bool _processing_is_mt; public: G1CMRefProcTaskProxy(ProcessTask& proc_task, G1CollectedHeap* g1h, ConcurrentMark* cm) : AbstractGangTask("Process reference objects in parallel"), - _proc_task(proc_task), _g1h(g1h), _cm(cm) { } + _proc_task(proc_task), _g1h(g1h), _cm(cm) { + ReferenceProcessor* rp = _g1h->ref_processor_cm(); + _processing_is_mt = rp->processing_is_mt(); + } virtual void work(uint worker_id) { CMTask* marking_task = _cm->task(worker_id); G1CMIsAliveClosure g1_is_alive(_g1h); - G1CMParKeepAliveAndDrainClosure g1_par_keep_alive(_cm, marking_task); - G1CMParDrainMarkingStackClosure g1_par_drain(_cm, marking_task); + G1CMKeepAliveAndDrainClosure g1_par_keep_alive(_cm, marking_task); + G1CMDrainMarkingStackClosure g1_par_drain(_cm, marking_task, _processing_is_mt); _proc_task.work(worker_id, g1_is_alive, g1_par_keep_alive, g1_par_drain); } @@ -2372,6 +2357,7 @@ void G1CMRefProcTaskExecutor::execute(ProcessTask& proc_task) { assert(_workers != NULL, "Need parallel worker threads."); + assert(_g1h->ref_processor_cm()->processing_is_mt(), "processing is not MT"); G1CMRefProcTaskProxy proc_task_proxy(proc_task, _g1h, _cm); @@ -2399,6 +2385,7 @@ void G1CMRefProcTaskExecutor::execute(EnqueueTask& enq_task) { assert(_workers != NULL, "Need parallel worker threads."); + assert(_g1h->ref_processor_cm()->processing_is_mt(), "processing is not MT"); G1CMRefEnqueueTaskProxy enq_task_proxy(enq_task); @@ -2429,59 +2416,58 @@ // See the comment in G1CollectedHeap::ref_processing_init() // about how reference processing currently works in G1. - // Process weak references. + // Set the soft reference policy rp->setup_policy(clear_all_soft_refs); assert(_markStack.isEmpty(), "mark stack should be empty"); - G1CMKeepAliveClosure g1_keep_alive(g1h, this); - G1CMDrainMarkingStackClosure - g1_drain_mark_stack(this, &_markStack, &g1_keep_alive); - - // We use the work gang from the G1CollectedHeap and we utilize all - // the worker threads. - uint active_workers = g1h->workers() ? g1h->workers()->active_workers() : 1U; + // Non-MT instances 'Keep Alive' and 'Complete GC' oop closures. + G1CMKeepAliveAndDrainClosure g1_keep_alive(this, task(0)); + G1CMDrainMarkingStackClosure g1_drain_mark_stack(this, task(0), false); + + // We need at least one active thread. If reference processing is + // not multi-threaded we use the current (ConcurrentMarkThread) thread, + // otherwise we use the work gang from the G1CollectedHeap and we + // utilize all the worker threads we can. + uint active_workers = (rp->processing_is_mt() && g1h->workers() != NULL + ? g1h->workers()->active_workers() + : 1U); + active_workers = MAX2(MIN2(active_workers, _max_worker_id), 1U); G1CMRefProcTaskExecutor par_task_executor(g1h, this, g1h->workers(), active_workers); - if (rp->processing_is_mt()) { - // Set the degree of MT here. If the discovery is done MT, there - // may have been a different number of threads doing the discovery - // and a different number of discovered lists may have Ref objects. - // That is OK as long as the Reference lists are balanced (see - // balance_all_queues() and balance_queues()). - rp->set_active_mt_degree(active_workers); - - rp->process_discovered_references(&g1_is_alive, + AbstractRefProcTaskExecutor* executor = (rp->processing_is_mt() + ? &par_task_executor + : NULL); + + // Set the degree of MT processing here. If the discovery was done MT, + // the number of threads involved during discovery could differ from + // the number of active workers. This is OK as long as the discovered + // Reference lists are balanced (see balance_all_queues() and balance_queues()). + rp->set_active_mt_degree(active_workers); + + // Process the weak references. + rp->process_discovered_references(&g1_is_alive, &g1_keep_alive, &g1_drain_mark_stack, - &par_task_executor); - - // The work routines of the parallel keep_alive and drain_marking_stack - // will set the has_overflown flag if we overflow the global marking - // stack. - } else { - rp->process_discovered_references(&g1_is_alive, - &g1_keep_alive, - &g1_drain_mark_stack, - NULL); - } + executor); + + // The do_oop work routines of the keep_alive and drain_marking_stack + // oop closures will set the has_overflown flag if we overflow the + // global marking stack. assert(_markStack.overflow() || _markStack.isEmpty(), "mark stack should be empty (unless it overflowed)"); if (_markStack.overflow()) { - // Should have been done already when we tried to push an + // This should have been done already when we tried to push an // entry on to the global mark stack. But let's do it again. set_has_overflown(); } - if (rp->processing_is_mt()) { - assert(rp->num_q() == active_workers, "why not"); - rp->enqueue_discovered_references(&par_task_executor); - } else { - rp->enqueue_discovered_references(); - } + assert(rp->num_q() == active_workers, "why not"); + + rp->enqueue_discovered_references(executor); rp->verify_no_references_recorded(); assert(!rp->discovery_enabled(), "Post condition"); diff -r 84304a77c4e3 -r f90b9bceb8e5 src/share/vm/gc_implementation/g1/concurrentMark.hpp --- a/src/share/vm/gc_implementation/g1/concurrentMark.hpp Mon Feb 04 19:40:27 2013 -0800 +++ b/src/share/vm/gc_implementation/g1/concurrentMark.hpp Tue Feb 05 09:13:05 2013 -0800 @@ -371,8 +371,8 @@ friend class CalcLiveObjectsClosure; friend class G1CMRefProcTaskProxy; friend class G1CMRefProcTaskExecutor; - friend class G1CMParKeepAliveAndDrainClosure; - friend class G1CMParDrainMarkingStackClosure; + friend class G1CMKeepAliveAndDrainClosure; + friend class G1CMDrainMarkingStackClosure; protected: ConcurrentMarkThread* _cmThread; // the thread doing the work