--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/vm/gc_implementation/g1/g1MonitoringSupport.hpp	Thu Apr 21 10:23:44 2011 -0700
@@ -0,0 +1,203 @@
+/*
+ * Copyright (c) 2011, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1MONITORINGSUPPORT_HPP
+#define SHARE_VM_GC_IMPLEMENTATION_G1_G1MONITORINGSUPPORT_HPP
+
+#include "gc_implementation/shared/hSpaceCounters.hpp"
+
+class G1CollectedHeap;
+class G1SpaceMonitoringSupport;
+
+// Class for monitoring logical spaces in G1.
+// G1 defines a set of regions as a young
+// collection (analogous to a young generation).
+// The young collection is a logical generation
+// with no fixed chunk (see space.hpp) reflecting
+// the address space for the generation.  In addition
+// to the young collection there is its complement
+// the non-young collection that is simply the regions
+// not in the young collection.  The non-young collection
+// is treated here as a logical old generation only
+// because the monitoring tools expect a generational
+// heap.  The monitoring tools expect that a Space
+// (see space.hpp) exists that describe the
+// address space of young collection and non-young
+// collection and such a view is provided here.
+//
+// This class provides interfaces to access
+// the value of variables for the young collection
+// that include the "capacity" and "used" of the
+// young collection along with constant values
+// for the minimum and maximum capacities for
+// the logical spaces.  Similarly for the non-young
+// collection.
+//
+// Also provided are counters for G1 concurrent collections
+// and stop-the-world full heap collecitons.
+//
+// Below is a description of how "used" and "capactiy"
+// (or committed) is calculated for the logical spaces.
+//
+// 1) The used space calculation for a pool is not necessarily
+// independent of the others. We can easily get from G1 the overall
+// used space in the entire heap, the number of regions in the young
+// generation (includes both eden and survivors), and the number of
+// survivor regions. So, from that we calculate:
+//
+//  survivor_used = survivor_num * region_size
+//  eden_used     = young_region_num * region_size - survivor_used
+//  old_gen_used  = overall_used - eden_used - survivor_used
+//
+// Note that survivor_used and eden_used are upper bounds. To get the
+// actual value we would have to iterate over the regions and add up
+// ->used(). But that'd be expensive. So, we'll accept some lack of
+// accuracy for those two. But, we have to be careful when calculating
+// old_gen_used, in case we subtract from overall_used more then the
+// actual number and our result goes negative.
+//
+// 2) Calculating the used space is straightforward, as described
+// above. However, how do we calculate the committed space, given that
+// we allocate space for the eden, survivor, and old gen out of the
+// same pool of regions? One way to do this is to use the used value
+// as also the committed value for the eden and survivor spaces and
+// then calculate the old gen committed space as follows:
+//
+//  old_gen_committed = overall_committed - eden_committed - survivor_committed
+//
+// Maybe a better way to do that would be to calculate used for eden
+// and survivor as a sum of ->used() over their regions and then
+// calculate committed as region_num * region_size (i.e., what we use
+// to calculate the used space now). This is something to consider
+// in the future.
+//
+// 3) Another decision that is again not straightforward is what is
+// the max size that each memory pool can grow to. One way to do this
+// would be to use the committed size for the max for the eden and
+// survivors and calculate the old gen max as follows (basically, it's
+// a similar pattern to what we use for the committed space, as
+// described above):
+//
+//  old_gen_max = overall_max - eden_max - survivor_max
+//
+// Unfortunately, the above makes the max of each pool fluctuate over
+// time and, even though this is allowed according to the spec, it
+// broke several assumptions in the M&M framework (there were cases
+// where used would reach a value greater than max). So, for max we
+// use -1, which means "undefined" according to the spec.
+//
+// 4) Now, there is a very subtle issue with all the above. The
+// framework will call get_memory_usage() on the three pools
+// asynchronously. As a result, each call might get a different value
+// for, say, survivor_num which will yield inconsistent values for
+// eden_used, survivor_used, and old_gen_used (as survivor_num is used
+// in the calculation of all three). This would normally be
+// ok. However, it's possible that this might cause the sum of
+// eden_used, survivor_used, and old_gen_used to go over the max heap
+// size and this seems to sometimes cause JConsole (and maybe other
+// clients) to get confused. There's not a really an easy / clean
+// solution to this problem, due to the asynchrounous nature of the
+// framework.
+
+class G1MonitoringSupport : public CHeapObj {
+  G1CollectedHeap* _g1h;
+  VirtualSpace* _g1_storage_addr;
+
+  // jstat performance counters
+  //  incremental collections both fully and partially young
+  CollectorCounters*   _incremental_collection_counters;
+  //  full stop-the-world collections
+  CollectorCounters*   _full_collection_counters;
+  //  young collection set counters.  The _eden_counters,
+  // _from_counters, and _to_counters are associated with
+  // this "generational" counter.
+  GenerationCounters*  _young_collection_counters;
+  //  non-young collection set counters. The _old_space_counters
+  // below are associated with this "generational" counter.
+  GenerationCounters*  _non_young_collection_counters;
+  // Counters for the capacity and used for
+  //   the whole heap
+  HSpaceCounters*      _old_space_counters;
+  //   the young collection
+  HSpaceCounters*      _eden_counters;
+  //   the survivor collection (only one, _to_counters, is actively used)
+  HSpaceCounters*      _from_counters;
+  HSpaceCounters*      _to_counters;
+
+  // It returns x - y if x > y, 0 otherwise.
+  // As described in the comment above, some of the inputs to the
+  // calculations we have to do are obtained concurrently and hence
+  // may be inconsistent with each other. So, this provides a
+  // defensive way of performing the subtraction and avoids the value
+  // going negative (which would mean a very large result, given that
+  // the parameter are size_t).
+  static size_t subtract_up_to_zero(size_t x, size_t y) {
+    if (x > y) {
+      return x - y;
+    } else {
+      return 0;
+    }
+  }
+
+ public:
+  G1MonitoringSupport(G1CollectedHeap* g1h, VirtualSpace* g1_storage_addr);
+
+  G1CollectedHeap* g1h() { return _g1h; }
+  VirtualSpace* g1_storage_addr() { return _g1_storage_addr; }
+
+  // Performance Counter accessors
+  void update_counters();
+  void update_eden_counters();
+
+  CollectorCounters* incremental_collection_counters() {
+    return _incremental_collection_counters;
+  }
+  CollectorCounters* full_collection_counters() {
+    return _full_collection_counters;
+  }
+  GenerationCounters* non_young_collection_counters() {
+    return _non_young_collection_counters;
+  }
+  HSpaceCounters*      old_space_counters() { return _old_space_counters; }
+  HSpaceCounters*      eden_counters() { return _eden_counters; }
+  HSpaceCounters*      from_counters() { return _from_counters; }
+  HSpaceCounters*      to_counters() { return _to_counters; }
+
+  // Monitoring support used by
+  //   MemoryService
+  //   jstat counters
+  size_t overall_committed();
+  size_t overall_used();
+
+  size_t eden_space_committed();
+  size_t eden_space_used();
+
+  size_t survivor_space_committed();
+  size_t survivor_space_used();
+
+  size_t old_space_committed();
+  size_t old_space_used();
+};
+
+#endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1MONITORINGSUPPORT_HPP