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 #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