46   g1h->do_collection_pause_at_safepoint();

    51   if (_should_initiate_conc_mark) {

    52     // It's safer to read full_collections_completed() here, given

    53     // that noone else will be updating it concurrently. Since we'll

    54     // only need it if we're initiating a marking cycle, no point in

    55     // setting it earlier.

    56     _full_collections_completed_before = g1h->full_collections_completed();

    57 

    58     // At this point we are supposed to start a concurrent cycle. We

    59     // will do so if one is not already in progress.

    60     bool res = g1h->g1_policy()->force_initial_mark_if_outside_cycle();

    61   }

    62   g1h->do_collection_pause_at_safepoint(_target_pause_time_ms);

    63 }

    64 

    65 void VM_G1IncCollectionPause::doit_epilogue() {

    66   VM_GC_Operation::doit_epilogue();

    67 

    68   // If the pause was initiated by a System.gc() and

    69   // +ExplicitGCInvokesConcurrent, we have to wait here for the cycle

    70   // that just started (or maybe one that was already in progress) to

    71   // finish.

    72   if (_gc_cause == GCCause::_java_lang_system_gc &&

    73       _should_initiate_conc_mark) {

    74     assert(ExplicitGCInvokesConcurrent,

    75            "the only way to be here is if ExplicitGCInvokesConcurrent is set");

    76 

    77     G1CollectedHeap* g1h = G1CollectedHeap::heap();

    78 

    79     // In the doit() method we saved g1h->full_collections_completed()

    80     // in the _full_collections_completed_before field. We have to

    81     // wait until we observe that g1h->full_collections_completed()

    82     // has increased by at least one. This can happen if a) we started

    83     // a cycle and it completes, b) a cycle already in progress

    84     // completes, or c) a Full GC happens.

    85 

    86     // If the condition has already been reached, there's no point in

    87     // actually taking the lock and doing the wait.

    88     if (g1h->full_collections_completed() <=

    89                                           _full_collections_completed_before) {

    90       // The following is largely copied from CMS

    91 

    92       Thread* thr = Thread::current();

    93       assert(thr->is_Java_thread(), "invariant");

    94       JavaThread* jt = (JavaThread*)thr;

    95       ThreadToNativeFromVM native(jt);

    96 

    97       MutexLockerEx x(FullGCCount_lock, Mutex::_no_safepoint_check_flag);

    98       while (g1h->full_collections_completed() <=

    99                                           _full_collections_completed_before) {

   100         FullGCCount_lock->wait(Mutex::_no_safepoint_check_flag);

   101       }

   102     }

   103   }