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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