hotspot/src/share/vm/gc/shared/barrierSet.hpp

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#ifndef SHARE_VM_GC_SHARED_BARRIERSET_HPP
#define SHARE_VM_GC_SHARED_BARRIERSET_HPP

#include "memory/memRegion.hpp"
#include "oops/oopsHierarchy.hpp"
#include "utilities/fakeRttiSupport.hpp"

// This class provides the interface between a barrier implementation and
// the rest of the system.

class BarrierSet: public CHeapObj<mtGC> {
  friend class VMStructs;
public:
  // Fake RTTI support.  For a derived class T to participate
  // - T must have a corresponding Name entry.
  // - GetName<T> must be specialized to return the corresponding Name
  //   entry.
  // - If T is a base class, the constructor must have a FakeRtti
  //   parameter and pass it up to its base class, with the tag set
  //   augmented with the corresponding Name entry.
  // - If T is a concrete class, the constructor must create a
  //   FakeRtti object whose tag set includes the corresponding Name
  //   entry, and pass it up to its base class.

  enum Name {                   // associated class
    ModRef,                     // ModRefBarrierSet
    CardTableModRef,            // CardTableModRefBS
    CardTableForRS,             // CardTableModRefBSForCTRS
    CardTableExtension,         // CardTableExtension
    G1SATBCT,                   // G1SATBCardTableModRefBS
    G1SATBCTLogging             // G1SATBCardTableLoggingModRefBS
  };

protected:
  typedef FakeRttiSupport<BarrierSet, Name> FakeRtti;

private:
  FakeRtti _fake_rtti;

  // Metafunction mapping a class derived from BarrierSet to the
  // corresponding Name enum tag.
  template<typename T> struct GetName;

  // Downcast argument to a derived barrier set type.
  // The cast is checked in a debug build.
  // T must have a specialization for BarrierSet::GetName<T>.
  template<typename T> friend T* barrier_set_cast(BarrierSet* bs);

public:
  // Note: This is not presently the Name corresponding to the
  // concrete class of this object.
  BarrierSet::Name kind() const { return _fake_rtti.concrete_tag(); }

  // Test whether this object is of the type corresponding to bsn.
  bool is_a(BarrierSet::Name bsn) const { return _fake_rtti.has_tag(bsn); }

  // End of fake RTTI support.

public:
  enum Flags {
    None                = 0,
    TargetUninitialized = 1
  };

protected:
  // Some barrier sets create tables whose elements correspond to parts of
  // the heap; the CardTableModRefBS is an example.  Such barrier sets will
  // normally reserve space for such tables, and commit parts of the table
  // "covering" parts of the heap that are committed. At most one covered
  // region per generation is needed.
  static const int _max_covered_regions = 2;

  BarrierSet(const FakeRtti& fake_rtti) : _fake_rtti(fake_rtti) { }
  ~BarrierSet() { }

public:

  // These operations indicate what kind of barriers the BarrierSet has.
  virtual bool has_read_ref_barrier() = 0;
  virtual bool has_read_prim_barrier() = 0;
  virtual bool has_write_ref_barrier() = 0;
  virtual bool has_write_ref_pre_barrier() = 0;
  virtual bool has_write_prim_barrier() = 0;

  // These functions indicate whether a particular access of the given
  // kinds requires a barrier.
  virtual bool read_ref_needs_barrier(void* field) = 0;
  virtual bool read_prim_needs_barrier(HeapWord* field, size_t bytes) = 0;
  virtual bool write_prim_needs_barrier(HeapWord* field, size_t bytes,
                                        juint val1, juint val2) = 0;

  // The first four operations provide a direct implementation of the
  // barrier set.  An interpreter loop, for example, could call these
  // directly, as appropriate.

  // Invoke the barrier, if any, necessary when reading the given ref field.
  virtual void read_ref_field(void* field) = 0;

  // Invoke the barrier, if any, necessary when reading the given primitive
  // "field" of "bytes" bytes in "obj".
  virtual void read_prim_field(HeapWord* field, size_t bytes) = 0;

  // Invoke the barrier, if any, necessary when writing "new_val" into the
  // ref field at "offset" in "obj".
  // (For efficiency reasons, this operation is specialized for certain
  // barrier types.  Semantically, it should be thought of as a call to the
  // virtual "_work" function below, which must implement the barrier.)
  // First the pre-write versions...
  template <class T> inline void write_ref_field_pre(T* field, oop new_val);
private:
  // Helper for write_ref_field_pre and friends, testing for specialized cases.
  bool devirtualize_reference_writes() const;

  // Keep this private so as to catch violations at build time.
  virtual void write_ref_field_pre_work(     void* field, oop new_val) { guarantee(false, "Not needed"); };
protected:
  virtual void write_ref_field_pre_work(      oop* field, oop new_val) {};
  virtual void write_ref_field_pre_work(narrowOop* field, oop new_val) {};
public:

  // ...then the post-write version.
  inline void write_ref_field(void* field, oop new_val, bool release = false);
protected:
  virtual void write_ref_field_work(void* field, oop new_val, bool release) = 0;
public:

  // Invoke the barrier, if any, necessary when writing the "bytes"-byte
  // value(s) "val1" (and "val2") into the primitive "field".
  virtual void write_prim_field(HeapWord* field, size_t bytes,
                                juint val1, juint val2) = 0;

  // Operations on arrays, or general regions (e.g., for "clone") may be
  // optimized by some barriers.

  // The first six operations tell whether such an optimization exists for
  // the particular barrier.
  virtual bool has_read_ref_array_opt() = 0;
  virtual bool has_read_prim_array_opt() = 0;
  virtual bool has_write_ref_array_pre_opt() { return true; }
  virtual bool has_write_ref_array_opt() = 0;
  virtual bool has_write_prim_array_opt() = 0;

  virtual bool has_read_region_opt() = 0;
  virtual bool has_write_region_opt() = 0;

  // These operations should assert false unless the corresponding operation
  // above returns true.  Otherwise, they should perform an appropriate
  // barrier for an array whose elements are all in the given memory region.
  virtual void read_ref_array(MemRegion mr) = 0;
  virtual void read_prim_array(MemRegion mr) = 0;

  // Below length is the # array elements being written
  virtual void write_ref_array_pre(oop* dst, int length,
                                   bool dest_uninitialized = false) {}
  virtual void write_ref_array_pre(narrowOop* dst, int length,
                                   bool dest_uninitialized = false) {}
  // Below count is the # array elements being written, starting
  // at the address "start", which may not necessarily be HeapWord-aligned
  inline void write_ref_array(HeapWord* start, size_t count);

  // Static versions, suitable for calling from generated code;
  // count is # array elements being written, starting with "start",
  // which may not necessarily be HeapWord-aligned.
  static void static_write_ref_array_pre(HeapWord* start, size_t count);
  static void static_write_ref_array_post(HeapWord* start, size_t count);

protected:
  virtual void write_ref_array_work(MemRegion mr) = 0;
public:
  virtual void write_prim_array(MemRegion mr) = 0;

  virtual void read_region(MemRegion mr) = 0;

  // (For efficiency reasons, this operation is specialized for certain
  // barrier types.  Semantically, it should be thought of as a call to the
  // virtual "_work" function below, which must implement the barrier.)
  void write_region(MemRegion mr);
protected:
  virtual void write_region_work(MemRegion mr) = 0;
public:
  // Inform the BarrierSet that the the covered heap region that starts
  // with "base" has been changed to have the given size (possibly from 0,
  // for initialization.)
  virtual void resize_covered_region(MemRegion new_region) = 0;

  // If the barrier set imposes any alignment restrictions on boundaries
  // within the heap, this function tells whether they are met.
  virtual bool is_aligned(HeapWord* addr) = 0;

  // Print a description of the memory for the barrier set
  virtual void print_on(outputStream* st) const = 0;
};

template<typename T>
inline T* barrier_set_cast(BarrierSet* bs) {
  assert(bs->is_a(BarrierSet::GetName<T>::value), "wrong type of barrier set");
  return static_cast<T*>(bs);
}

#endif // SHARE_VM_GC_SHARED_BARRIERSET_HPP