src/hotspot/share/memory/iterator.hpp

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 *
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 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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#ifndef SHARE_MEMORY_ITERATOR_HPP
#define SHARE_MEMORY_ITERATOR_HPP

#include "memory/allocation.hpp"
#include "memory/memRegion.hpp"
#include "oops/oopsHierarchy.hpp"

class CodeBlob;
class nmethod;
class ReferenceDiscoverer;
class DataLayout;
class KlassClosure;
class ClassLoaderData;
class Symbol;
class Metadata;
class Thread;

// The following classes are C++ `closures` for iterating over objects, roots and spaces

class Closure : public StackObj { };

// Thread iterator
class ThreadClosure {
 public:
  virtual void do_thread(Thread* thread) = 0;
};

// OopClosure is used for iterating through references to Java objects.
class OopClosure : public Closure {
 public:
  virtual void do_oop(oop* o) = 0;
  virtual void do_oop(narrowOop* o) = 0;
};

class DoNothingClosure : public OopClosure {
 public:
  virtual void do_oop(oop* p)       {}
  virtual void do_oop(narrowOop* p) {}
};
extern DoNothingClosure do_nothing_cl;

// OopIterateClosure adds extra code to be run during oop iterations.
// This is needed by the GC and is extracted to a separate type to not
// pollute the OopClosure interface.
class OopIterateClosure : public OopClosure {
 private:
  ReferenceDiscoverer* _ref_discoverer;

 protected:
  OopIterateClosure(ReferenceDiscoverer* rd) : _ref_discoverer(rd) { }
  OopIterateClosure() : _ref_discoverer(nullptr) { }
  ~OopIterateClosure() { }

  void set_ref_discoverer_internal(ReferenceDiscoverer* rd) { _ref_discoverer = rd; }

 public:
  ReferenceDiscoverer* ref_discoverer() const { return _ref_discoverer; }

  // Iteration of InstanceRefKlasses differ depending on the closure,
  // the below enum describes the different alternatives.
  enum ReferenceIterationMode {
    DO_DISCOVERY,                // Apply closure and discover references
    DO_FIELDS,                   // Apply closure to all fields
    DO_FIELDS_EXCEPT_REFERENT    // Apply closure to all fields except the referent field
  };

  // The default iteration mode is to do discovery.
  virtual ReferenceIterationMode reference_iteration_mode() { return DO_DISCOVERY; }

  // If the do_metadata functions return "true",
  // we invoke the following when running oop_iterate():
  //
  // 1) do_klass on the header klass pointer.
  // 2) do_klass on the klass pointer in the mirrors.
  // 3) do_cld   on the class loader data in class loaders.
  //
  // Used to determine metadata liveness for class unloading GCs.

  virtual bool do_metadata() = 0;
  virtual void do_klass(Klass* k) = 0;
  virtual void do_cld(ClassLoaderData* cld) = 0;

  // Class redefinition needs to get notified about methods from stackChunkOops
  virtual void do_method(Method* m) = 0;
  // The code cache unloading needs to get notified about methods from stackChunkOops
  virtual void do_nmethod(nmethod* nm) = 0;
};

// An OopIterateClosure that can be used when there's no need to visit the Metadata.
class BasicOopIterateClosure : public OopIterateClosure {
public:
  BasicOopIterateClosure(ReferenceDiscoverer* rd = nullptr) : OopIterateClosure(rd) {}

  virtual bool do_metadata() { return false; }
  virtual void do_klass(Klass* k) { ShouldNotReachHere(); }
  virtual void do_cld(ClassLoaderData* cld) { ShouldNotReachHere(); }
  virtual void do_method(Method* m) { ShouldNotReachHere(); }
  virtual void do_nmethod(nmethod* nm) { ShouldNotReachHere(); }
};

// Interface for applying an OopClosure to a set of oops.
class OopIterator {
public:
  virtual void oops_do(OopClosure* cl) = 0;
};

enum class derived_base : intptr_t;
enum class derived_pointer : intptr_t;
class DerivedOopClosure : public Closure {
 public:
  enum { SkipNull = true };
  virtual void do_derived_oop(derived_base* base, derived_pointer* derived) = 0;
};

class KlassClosure : public Closure {
 public:
  virtual void do_klass(Klass* k) = 0;
};

class CLDClosure : public Closure {
 public:
  virtual void do_cld(ClassLoaderData* cld) = 0;
};

class MetadataClosure : public Closure {
 public:
  virtual void do_metadata(Metadata* md) = 0;
};


class CLDToOopClosure : public CLDClosure {
  OopClosure*       _oop_closure;
  int               _cld_claim;

 public:
  CLDToOopClosure(OopClosure* oop_closure,
                  int cld_claim) :
      _oop_closure(oop_closure),
      _cld_claim(cld_claim) {}

  void do_cld(ClassLoaderData* cld);
};

template <int claim>
class ClaimingCLDToOopClosure : public CLDToOopClosure {
public:
  ClaimingCLDToOopClosure(OopClosure* cl) : CLDToOopClosure(cl, claim) {}
};

class ClaimMetadataVisitingOopIterateClosure : public OopIterateClosure {
 protected:
  const int _claim;

 public:
  ClaimMetadataVisitingOopIterateClosure(int claim, ReferenceDiscoverer* rd = nullptr) :
      OopIterateClosure(rd),
      _claim(claim) { }

  virtual bool do_metadata() { return true; }
  virtual void do_klass(Klass* k);
  virtual void do_cld(ClassLoaderData* cld);
  virtual void do_method(Method* m);
  virtual void do_nmethod(nmethod* nm);
};

// The base class for all concurrent marking closures,
// that participates in class unloading.
// It's used to proxy through the metadata to the oops defined in them.
class MetadataVisitingOopIterateClosure: public ClaimMetadataVisitingOopIterateClosure {
 public:
  MetadataVisitingOopIterateClosure(ReferenceDiscoverer* rd = nullptr);
};

// ObjectClosure is used for iterating through an object space

class ObjectClosure : public Closure {
 public:
  // Called for each object.
  virtual void do_object(oop obj) = 0;
};

class BoolObjectClosure : public Closure {
 public:
  virtual bool do_object_b(oop obj) = 0;
};

class OopFieldClosure {
public:
  virtual void do_field(oop base, oop* p) = 0;
};

class AlwaysTrueClosure: public BoolObjectClosure {
 public:
  bool do_object_b(oop p) { return true; }
};

class AlwaysFalseClosure : public BoolObjectClosure {
 public:
  bool do_object_b(oop p) { return false; }
};

// Applies an oop closure to all ref fields in objects iterated over in an
// object iteration.
class ObjectToOopClosure: public ObjectClosure {
  OopIterateClosure* _cl;
public:
  void do_object(oop obj);
  ObjectToOopClosure(OopIterateClosure* cl) : _cl(cl) {}
};

// NMethodClosure is used for iterating through nmethods
// in the code cache or on thread stacks

class NMethodClosure : public Closure {
 public:
  virtual void do_nmethod(nmethod* n) = 0;
};

// Applies an oop closure to all ref fields in nmethods
// iterated over in an object iteration.
class NMethodToOopClosure : public NMethodClosure {
 protected:
  OopClosure* _cl;
  bool _fix_relocations;
 public:
  // If fix_relocations(), then cl must copy objects to their new location immediately to avoid
  // patching nmethods with the old locations.
  NMethodToOopClosure(OopClosure* cl, bool fix_relocations) : _cl(cl), _fix_relocations(fix_relocations) {}
  void do_nmethod(nmethod* nm) override;

  bool fix_relocations() const { return _fix_relocations; }
  const static bool FixRelocations = true;
};

class MarkingNMethodClosure : public NMethodToOopClosure {
  bool _keepalive_nmethods;

 public:
  MarkingNMethodClosure(OopClosure* cl, bool fix_relocations, bool keepalive_nmethods) :
      NMethodToOopClosure(cl, fix_relocations),
      _keepalive_nmethods(keepalive_nmethods) {}

  // Called for each nmethod.
  virtual void do_nmethod(nmethod* nm);
};

// MonitorClosure is used for iterating over monitors in the monitors cache

class ObjectMonitor;

class MonitorClosure : public StackObj {
 public:
  // called for each monitor in cache
  virtual void do_monitor(ObjectMonitor* m) = 0;
};

// A closure that is applied without any arguments.
class VoidClosure : public StackObj {
 public:
  virtual void do_void() = 0;
};


// YieldClosure is intended for use by iteration loops
// to incrementalize their work, allowing interleaving
// of an interruptible task so as to allow other
// threads to run (which may not otherwise be able to access
// exclusive resources, for instance). Additionally, the
// closure also allows for aborting an ongoing iteration
// by means of checking the return value from the polling
// call.
class YieldClosure : public StackObj {
public:
 virtual bool should_return() = 0;

 // Yield on a fine-grain level. The check in case of not yielding should be very fast.
 virtual bool should_return_fine_grain() { return false; }
};

class SymbolClosure : public StackObj {
 public:
  virtual void do_symbol(Symbol**) = 0;
};

template <typename E>
class CompareClosure : public Closure {
public:
    virtual int do_compare(const E&, const E&) = 0;
};

class OopIteratorClosureDispatch {
 public:
  template <typename OopClosureType> static void oop_oop_iterate(OopClosureType* cl, oop obj, Klass* klass);
  template <typename OopClosureType> static void oop_oop_iterate(OopClosureType* cl, oop obj, Klass* klass, MemRegion mr);
  template <typename OopClosureType> static void oop_oop_iterate_backwards(OopClosureType* cl, oop obj, Klass* klass);
};

#endif // SHARE_MEMORY_ITERATOR_HPP