--- a/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp	Mon Jun 28 14:13:18 2010 -0400
+++ b/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp	Mon Jun 28 14:13:17 2010 -0400
@@ -809,7 +809,8 @@
   }
 };
 
-void G1CollectedHeap::do_collection(bool full, bool clear_all_soft_refs,
+void G1CollectedHeap::do_collection(bool explicit_gc,
+                                    bool clear_all_soft_refs,
                                     size_t word_size) {
   if (GC_locker::check_active_before_gc()) {
     return; // GC is disabled (e.g. JNI GetXXXCritical operation)
@@ -821,10 +822,6 @@
     Universe::print_heap_before_gc();
   }
 
-  if (full && DisableExplicitGC) {
-    return;
-  }
-
   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
   assert(Thread::current() == VMThread::vm_thread(), "should be in vm thread");
 
@@ -837,9 +834,11 @@
     IsGCActiveMark x;
 
     // Timing
+    bool system_gc = (gc_cause() == GCCause::_java_lang_system_gc);
+    assert(!system_gc || explicit_gc, "invariant");
     gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
-    TraceTime t(full ? "Full GC (System.gc())" : "Full GC",
+    TraceTime t(system_gc ? "Full GC (System.gc())" : "Full GC",
                 PrintGC, true, gclog_or_tty);
 
     TraceMemoryManagerStats tms(true /* fullGC */);
@@ -944,7 +943,7 @@
     heap_region_iterate(&rs_clear);
 
     // Resize the heap if necessary.
-    resize_if_necessary_after_full_collection(full ? 0 : word_size);
+    resize_if_necessary_after_full_collection(explicit_gc ? 0 : word_size);
 
     if (_cg1r->use_cache()) {
       _cg1r->clear_and_record_card_counts();
@@ -1009,13 +1008,18 @@
             "young list should be empty at this point");
   }
 
+  // Update the number of full collections that have been completed.
+  increment_full_collections_completed(false /* outer */);
+
   if (PrintHeapAtGC) {
     Universe::print_heap_after_gc();
   }
 }
 
 void G1CollectedHeap::do_full_collection(bool clear_all_soft_refs) {
-  do_collection(true, clear_all_soft_refs, 0);
+  do_collection(true,                /* explicit_gc */
+                clear_all_soft_refs,
+                0                    /* word_size */);
 }
 
 // This code is mostly copied from TenuredGeneration.
@@ -1331,6 +1335,7 @@
   _young_list(new YoungList(this)),
   _gc_time_stamp(0),
   _surviving_young_words(NULL),
+  _full_collections_completed(0),
   _in_cset_fast_test(NULL),
   _in_cset_fast_test_base(NULL),
   _dirty_cards_region_list(NULL) {
@@ -1689,6 +1694,51 @@
   return car->free();
 }
 
+bool G1CollectedHeap::should_do_concurrent_full_gc(GCCause::Cause cause) {
+  return
+    ((cause == GCCause::_gc_locker           && GCLockerInvokesConcurrent) ||
+     (cause == GCCause::_java_lang_system_gc && ExplicitGCInvokesConcurrent));
+}
+
+void G1CollectedHeap::increment_full_collections_completed(bool outer) {
+  MonitorLockerEx x(FullGCCount_lock, Mutex::_no_safepoint_check_flag);
+
+  // We have already incremented _total_full_collections at the start
+  // of the GC, so total_full_collections() represents how many full
+  // collections have been started.
+  unsigned int full_collections_started = total_full_collections();
+
+  // Given that this method is called at the end of a Full GC or of a
+  // concurrent cycle, and those can be nested (i.e., a Full GC can
+  // interrupt a concurrent cycle), the number of full collections
+  // completed should be either one (in the case where there was no
+  // nesting) or two (when a Full GC interrupted a concurrent cycle)
+  // behind the number of full collections started.
+
+  // This is the case for the inner caller, i.e. a Full GC.
+  assert(outer ||
+         (full_collections_started == _full_collections_completed + 1) ||
+         (full_collections_started == _full_collections_completed + 2),
+         err_msg("for inner caller: full_collections_started = %u "
+                 "is inconsistent with _full_collections_completed = %u",
+                 full_collections_started, _full_collections_completed));
+
+  // This is the case for the outer caller, i.e. the concurrent cycle.
+  assert(!outer ||
+         (full_collections_started == _full_collections_completed + 1),
+         err_msg("for outer caller: full_collections_started = %u "
+                 "is inconsistent with _full_collections_completed = %u",
+                 full_collections_started, _full_collections_completed));
+
+  _full_collections_completed += 1;
+
+  // This notify_all() will ensure that a thread that called
+  // System.gc() with (with ExplicitGCInvokesConcurrent set or not)
+  // and it's waiting for a full GC to finish will be woken up. It is
+  // waiting in VM_G1IncCollectionPause::doit_epilogue().
+  FullGCCount_lock->notify_all();
+}
+
 void G1CollectedHeap::collect_as_vm_thread(GCCause::Cause cause) {
   assert(Thread::current()->is_VM_thread(), "Precondition#1");
   assert(Heap_lock->is_locked(), "Precondition#2");
@@ -1709,25 +1759,41 @@
   // The caller doesn't have the Heap_lock
   assert(!Heap_lock->owned_by_self(), "this thread should not own the Heap_lock");
 
-  int gc_count_before;
+  unsigned int gc_count_before;
+  unsigned int full_gc_count_before;
   {
     MutexLocker ml(Heap_lock);
     // Read the GC count while holding the Heap_lock
     gc_count_before = SharedHeap::heap()->total_collections();
+    full_gc_count_before = SharedHeap::heap()->total_full_collections();
 
     // Don't want to do a GC until cleanup is completed.
     wait_for_cleanup_complete();
-  } // We give up heap lock; VMThread::execute gets it back below
-  switch (cause) {
-    case GCCause::_scavenge_alot: {
-      // Do an incremental pause, which might sometimes be abandoned.
-      VM_G1IncCollectionPause op(gc_count_before, cause);
+
+    // We give up heap lock; VMThread::execute gets it back below
+  }
+
+  if (should_do_concurrent_full_gc(cause)) {
+    // Schedule an initial-mark evacuation pause that will start a
+    // concurrent cycle.
+    VM_G1IncCollectionPause op(gc_count_before,
+                               true, /* should_initiate_conc_mark */
+                               g1_policy()->max_pause_time_ms(),
+                               cause);
+    VMThread::execute(&op);
+  } else {
+    if (cause == GCCause::_gc_locker
+        DEBUG_ONLY(|| cause == GCCause::_scavenge_alot)) {
+
+      // Schedule a standard evacuation pause.
+      VM_G1IncCollectionPause op(gc_count_before,
+                                 false, /* should_initiate_conc_mark */
+                                 g1_policy()->max_pause_time_ms(),
+                                 cause);
       VMThread::execute(&op);
-      break;
-    }
-    default: {
-      // In all other cases, we currently do a full gc.
-      VM_G1CollectFull op(gc_count_before, cause);
+    } else {
+      // Schedule a Full GC.
+      VM_G1CollectFull op(gc_count_before, full_gc_count_before, cause);
       VMThread::execute(&op);
     }
   }
@@ -1989,6 +2055,11 @@
 
 void G1CollectedHeap::collection_set_iterate_from(HeapRegion* r,
                                                   HeapRegionClosure *cl) {
+  if (r == NULL) {
+    // The CSet is empty so there's nothing to do.
+    return;
+  }
+
   assert(r->in_collection_set(),
          "Start region must be a member of the collection set.");
   HeapRegion* cur = r;
@@ -2481,11 +2552,13 @@
 }
 
 void G1CollectedHeap::do_collection_pause() {
+  assert(Heap_lock->owned_by_self(), "we assume we'reholding the Heap_lock");
+
   // Read the GC count while holding the Heap_lock
   // we need to do this _before_ wait_for_cleanup_complete(), to
   // ensure that we do not give up the heap lock and potentially
   // pick up the wrong count
-  int gc_count_before = SharedHeap::heap()->total_collections();
+  unsigned int gc_count_before = SharedHeap::heap()->total_collections();
 
   // Don't want to do a GC pause while cleanup is being completed!
   wait_for_cleanup_complete();
@@ -2493,7 +2566,10 @@
   g1_policy()->record_stop_world_start();
   {
     MutexUnlocker mu(Heap_lock);  // give up heap lock, execute gets it back
-    VM_G1IncCollectionPause op(gc_count_before);
+    VM_G1IncCollectionPause op(gc_count_before,
+                               false, /* should_initiate_conc_mark */
+                               g1_policy()->max_pause_time_ms(),
+                               GCCause::_g1_inc_collection_pause);
     VMThread::execute(&op);
   }
 }
@@ -2612,7 +2688,7 @@
 };
 
 void
-G1CollectedHeap::do_collection_pause_at_safepoint() {
+G1CollectedHeap::do_collection_pause_at_safepoint(double target_pause_time_ms) {
   if (GC_locker::check_active_before_gc()) {
     return; // GC is disabled (e.g. JNI GetXXXCritical operation)
   }
@@ -2637,8 +2713,12 @@
       else
         strcat(verbose_str, "(partial)");
     }
-    if (g1_policy()->during_initial_mark_pause())
+    if (g1_policy()->during_initial_mark_pause()) {
       strcat(verbose_str, " (initial-mark)");
+      // We are about to start a marking cycle, so we increment the
+      // full collection counter.
+      increment_total_full_collections();
+    }
 
     // if PrintGCDetails is on, we'll print long statistics information
     // in the collector policy code, so let's not print this as the output
@@ -2661,7 +2741,6 @@
              "young list should be well formed");
     }
 
-    bool abandoned = false;
     { // Call to jvmpi::post_class_unload_events must occur outside of active GC
       IsGCActiveMark x;
 
@@ -2743,7 +2822,7 @@
 
       // Now choose the CS. We may abandon a pause if we find no
       // region that will fit in the MMU pause.
-      bool abandoned = g1_policy()->choose_collection_set();
+      bool abandoned = g1_policy()->choose_collection_set(target_pause_time_ms);
 
       // Nothing to do if we were unable to choose a collection set.
       if (!abandoned) {