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#ifndef SHARE_VM_SERVICES_G1MEMORYPOOL_HPP

#define SHARE_VM_SERVICES_G1MEMORYPOOL_HPP

#ifndef SERIALGC

#include "services/memoryPool.hpp"

#include "services/memoryUsage.hpp"

#endif

class G1CollectedHeap;

// This file contains the three classes that represent the memory

// pools of the G1 spaces: G1EdenPool, G1SurvivorPool, and

// G1OldGenPool. In G1, unlike our other GCs, we do not have a

// physical space for each of those spaces. Instead, we allocate

// regions for all three spaces out of a single pool of regions (that

// pool basically covers the entire heap). As a result, the eden,

// survivor, and old gen are considered logical spaces in G1, as each

// is a set of non-contiguous regions. This is also reflected in the

// way we map them to memory pools here. The easiest way to have done

// this would have been to map the entire G1 heap to a single memory

// pool. However, it's helpful to show how large the eden and survivor

// get, as this does affect the performance and behavior of G1. Which

// is why we introduce the three memory pools implemented here.

//

// The above approach inroduces a couple of challenging issues in the

// implementation of the three memory pools:

//

// 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.

// This class is shared by the three G1 memory pool classes

// (G1EdenPool, G1SurvivorPool, G1OldGenPool). Given that the way we

// calculate used / committed bytes for these three pools is related

// (see comment above), we put the calculations in this class so that

// we can easily share them among the subclasses.

class G1MemoryPoolSuper : public CollectedMemoryPool {

private:

  // 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;

    }

  }

protected:

  G1CollectedHeap* _g1h;

  // Would only be called from subclasses.

  G1MemoryPoolSuper(G1CollectedHeap* g1h,

                    const char* name,

                    size_t init_size,

                    bool support_usage_threshold);

  // The reason why all the code is in static methods is so that it

  // can be safely called from the constructors of the subclasses.

  static size_t undefined_max() {

    return (size_t) -1;

  }

  static size_t overall_committed(G1CollectedHeap* g1h) {

    return g1h->capacity();

  }

  static size_t overall_used(G1CollectedHeap* g1h) {

    return g1h->used_unlocked();

  }

  static size_t eden_space_committed(G1CollectedHeap* g1h);

  static size_t eden_space_used(G1CollectedHeap* g1h);

  static size_t survivor_space_committed(G1CollectedHeap* g1h);

  static size_t survivor_space_used(G1CollectedHeap* g1h);

  static size_t old_space_committed(G1CollectedHeap* g1h);

  static size_t old_space_used(G1CollectedHeap* g1h);

};

// Memory pool that represents the G1 eden.

class G1EdenPool : public G1MemoryPoolSuper {

public:

  G1EdenPool(G1CollectedHeap* g1h);

  size_t used_in_bytes() {

    return eden_space_used(_g1h);

  }

  size_t max_size() const {

    return undefined_max();

  }

  MemoryUsage get_memory_usage();

};

// Memory pool that represents the G1 survivor.

class G1SurvivorPool : public G1MemoryPoolSuper {

public:

  G1SurvivorPool(G1CollectedHeap* g1h);

  size_t used_in_bytes() {

    return survivor_space_used(_g1h);

  }

  size_t max_size() const {

    return undefined_max();

  }

  MemoryUsage get_memory_usage();

};

// Memory pool that represents the G1 old gen.

class G1OldGenPool : public G1MemoryPoolSuper {

public:

  G1OldGenPool(G1CollectedHeap* g1h);

  size_t used_in_bytes() {

    return old_space_used(_g1h);

  }

  size_t max_size() const {

    return undefined_max();

  }

  MemoryUsage get_memory_usage();

};

#endif // SHARE_VM_SERVICES_G1MEMORYPOOL_HPP