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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 for monitoring logical spaces in G1. It provides data for

 // both G1's jstat counters as well as G1's memory pools.

 //

 // G1 splits the heap into heap regions and each heap region belongs

 // to one of the following categories:

 //

 // * eden      : regions that have been allocated since the last GC

 // * survivors : regions with objects that survived the last few GCs

 // * old       : long-lived non-humongous regions

 // * humongous : humongous regions

 // * free      : free regions

 //

 // The combination of eden and survivor regions form the equivalent of

 // the young generation in the other GCs. The combination of old and

 // humongous regions form the equivalent of the old generation in the

 // other GCs. Free regions do not have a good equivalent in the other

 // GCs given that they can be allocated as any of the other region types.

 //

 // The monitoring tools expect the heap to contain a number of

 // generations (young, old, perm) and each generation to contain a

 // number of spaces (young: eden, survivors, old). Given that G1 does

 // not maintain those spaces physically (e.g., the set of

 // non-contiguous eden regions can be considered as a "logical"

 // space), we'll provide the illusion that those generations and

 // spaces exist. In reality, each generation and space refers to a set

 // of heap regions that are potentially non-contiguous.

 //

 // This class provides interfaces to access the min, current, and max

 // capacity and current occupancy for each of G1's logical spaces and

 // generations we expose to the monitoring tools. Also provided are

 // counters for G1 concurrent collections and stop-the-world full heap

 // collections.

 //

 // Below is a description of how the various sizes are calculated.

 //

 // * Current Capacity

 //

 //    - heap_capacity = current heap capacity (e.g., current committed size)

 //    - young_gen_capacity = current max young gen target capacity

 //          (i.e., young gen target capacity + max allowed expansion capacity)

 //    - survivor_capacity = current survivor region capacity

 //    - eden_capacity = young_gen_capacity - survivor_capacity

 //    - old_capacity = heap_capacity - young_gen_capacity

 //

 //    What we do in the above is to distribute the free regions among

 //    eden_capacity and old_capacity.

 //

 // * Occupancy

 //

 //    - young_gen_used = current young region capacity

 //    - survivor_used = survivor_capacity

 //    - eden_used = young_gen_used - survivor_used

 //    - old_used = overall_used - young_gen_used

 //

 //    Unfortunately, we currently only keep track of the number of

 //    currently allocated young and survivor regions + the overall used

 //    bytes in the heap, so the above can be a little inaccurate.

 //

 // * Min Capacity

 //

 //    We set this to 0 for all spaces.

 //

 // * Max Capacity

 //

 //    For jstat, we set the max capacity of all spaces to heap_capacity,

 //    given that we don't always have a reasonable upper bound on how big

 //    each space can grow. For the memory pools, we make the max

 //    capacity undefined with the exception of the old memory pool for

 //    which we make the max capacity same as the max heap capacity.

 //

 // If we had more accurate occupancy / capacity information per

 // region set the above calculations would be greatly simplified and

 // be made more accurate.

 //

 // We update all the above synchronously and we store the results in

 // fields so that we just read said fields when needed. A subtle point

 // is that all the above sizes need to be recalculated when the old

 // gen changes capacity (after a GC or after a humongous allocation)

 // but only the eden occupancy changes when a new eden region is

 // allocated. So, in the latter case we have minimal recalcuation to

 // do which is important as we want to keep the eden region allocation

 // path as low-overhead as possible.

 class G1MonitoringSupport : public CHeapObj<mtGC> {

   friend class VMStructs;

   G1CollectedHeap* _g1h;

   // jstat performance counters

   //  incremental collections both young and mixed

   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;

   //  old collection set counters. The _old_space_counters

   // below are associated with this "generational" counter.

   GenerationCounters*  _old_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;

   // When it's appropriate to recalculate the various sizes (at the

   // end of a GC, when a new eden region is allocated, etc.) we store

   // them here so that we can easily report them when needed and not

   // have to recalculate them every time.

   size_t _overall_reserved;

   size_t _overall_committed;

   size_t _overall_used;

   uint   _young_region_num;

   size_t _young_gen_committed;

   size_t _eden_committed;

   size_t _eden_used;

   size_t _survivor_committed;

   size_t _survivor_used;

   size_t _old_committed;

   size_t _old_used;

   G1CollectedHeap* g1h() { return _g1h; }

   // 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;

     }

   }

   // Recalculate all the sizes.

   void recalculate_sizes();

   // Recalculate only what's necessary when a new eden region is allocated.

   void recalculate_eden_size();

  public:

   G1MonitoringSupport(G1CollectedHeap* g1h);

   // Unfortunately, the jstat tool assumes that no space has 0

   // capacity. In our case, given that each space is logical, it's

   // possible that no regions will be allocated to it, hence to have 0

   // capacity (e.g., if there are no survivor regions, the survivor

   // space has 0 capacity). The way we deal with this is to always pad

   // each capacity value we report to jstat by a very small amount to

   // make sure that it's never zero. Given that we sometimes have to

   // report a capacity of a generation that contains several spaces

   // (e.g., young gen includes one eden, two survivor spaces), the

   // mult parameter is provided in order to adding the appropriate

   // padding multiple times so that the capacities add up correctly.

   static size_t pad_capacity(size_t size_bytes, size_t mult = 1) {

     return size_bytes + MinObjAlignmentInBytes * mult;

   }

   // Recalculate all the sizes from scratch and update all the jstat

   // counters accordingly.

   void update_sizes();

   // Recalculate only what's necessary when a new eden region is

   // allocated and update any jstat counters that need to be updated.

   void update_eden_size();

   CollectorCounters* incremental_collection_counters() {

     return _incremental_collection_counters;

   }

   CollectorCounters* full_collection_counters() {

     return _full_collection_counters;

   }

   GenerationCounters* young_collection_counters() {

     return _young_collection_counters;

   }

   GenerationCounters* old_collection_counters() {

     return _old_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_reserved()           { return _overall_reserved;     }

   size_t overall_committed()          { return _overall_committed;    }

   size_t overall_used()               { return _overall_used;         }

   size_t young_gen_committed()        { return _young_gen_committed;  }

   size_t young_gen_max()              { return overall_reserved();    }

   size_t eden_space_committed()       { return _eden_committed;       }

   size_t eden_space_used()            { return _eden_used;            }

   size_t survivor_space_committed()   { return _survivor_committed;   }

   size_t survivor_space_used()        { return _survivor_used;        }

   size_t old_gen_committed()          { return old_space_committed(); }

   size_t old_gen_max()                { return overall_reserved();    }

   size_t old_space_committed()        { return _old_committed;        }

   size_t old_space_used()             { return _old_used;             }

 };

 class G1GenerationCounters: public GenerationCounters {

 protected:

   G1MonitoringSupport* _g1mm;

 public:

   G1GenerationCounters(G1MonitoringSupport* g1mm,

                        const char* name, int ordinal, int spaces,

                        size_t min_capacity, size_t max_capacity,

                        size_t curr_capacity);

 };

 class G1YoungGenerationCounters: public G1GenerationCounters {

 public:

   G1YoungGenerationCounters(G1MonitoringSupport* g1mm, const char* name);

   virtual void update_all();

 };

 class G1OldGenerationCounters: public G1GenerationCounters {

 public:

   G1OldGenerationCounters(G1MonitoringSupport* g1mm, const char* name);

   virtual void update_all();

 };

 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1MONITORINGSUPPORT_HPP