src/hotspot/share/memory/iterator.hpp

/*
 * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

#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 Closure {
 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(NULL) { }
  ~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_DISCOVERED_AND_DISCOVERY, // Apply closure to discovered field and do discovery
    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.

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

#ifdef ASSERT
  // Default verification of each visited oop field.
  template <typename T> void verify(T* p);

  // Can be used by subclasses to turn off the default verification of oop fields.
  virtual bool should_verify_oops() { return true; }
#endif
};

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

  virtual bool do_metadata() { return false; }
  virtual void do_klass(Klass* k) { ShouldNotReachHere(); }
  virtual void do_cld(ClassLoaderData* cld) { ShouldNotReachHere(); }
};

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);
};

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

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

  virtual bool do_metadata() { return true; }
  virtual void do_klass(Klass* k);
  virtual void do_cld(ClassLoaderData* cld);
};

// 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 = NULL);
};

// 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 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) {}
};

// SpaceClosure is used for iterating over spaces

class Space;
class CompactibleSpace;

class SpaceClosure : public StackObj {
 public:
  // Called for each space
  virtual void do_space(Space* s) = 0;
};

class CompactibleSpaceClosure : public StackObj {
 public:
  // Called for each compactible space
  virtual void do_space(CompactibleSpace* s) = 0;
};


// CodeBlobClosure is used for iterating through code blobs
// in the code cache or on thread stacks

class CodeBlobClosure : public Closure {
 public:
  // Called for each code blob.
  virtual void do_code_blob(CodeBlob* cb) = 0;
};

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

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

class MarkingCodeBlobClosure : public CodeBlobToOopClosure {
 public:
  MarkingCodeBlobClosure(OopClosure* cl, bool fix_relocations) : CodeBlobToOopClosure(cl, fix_relocations) {}
  // Called for each code blob, but at most once per unique blob.

  virtual void do_code_blob(CodeBlob* cb);
};

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

// 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:
  // I would have liked to declare this a pure virtual, but that breaks
  // in mysterious ways, for unknown reasons.
  virtual void do_void();
};


// YieldClosure is intended for use by iteration loops
// to incrementalize their work, allowing interleaving
// of an interruptable 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; }
};

// Abstract closure for serializing data (read or write).

class SerializeClosure : public Closure {
public:
  // Return bool indicating whether closure implements read or write.
  virtual bool reading() const = 0;

  // Read/write the void pointer pointed to by p.
  virtual void do_ptr(void** p) = 0;

  // Read/write the 32-bit unsigned integer pointed to by p.
  virtual void do_u4(u4* p) = 0;

  // Read/write the bool pointed to by p.
  virtual void do_bool(bool* p) = 0;

  // Read/write the region specified.
  virtual void do_region(u_char* start, size_t size) = 0;

  // Check/write the tag.  If reading, then compare the tag against
  // the passed in value and fail is they don't match.  This allows
  // for verification that sections of the serialized data are of the
  // correct length.
  virtual void do_tag(int tag) = 0;

  // Read/write the oop
  virtual void do_oop(oop* o) = 0;

  bool writing() {
    return !reading();
  }
};

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

  // Clear LSB in symbol address; it can be set by CPSlot.
  static Symbol* load_symbol(Symbol** p) {
    return (Symbol*)(intptr_t(*p) & ~1);
  }

  // Store symbol, adjusting new pointer if the original pointer was adjusted
  // (symbol references in constant pool slots have their LSB set to 1).
  static void store_symbol(Symbol** p, Symbol* sym) {
    *p = (Symbol*)(intptr_t(sym) | (intptr_t(*p) & 1));
  }
};

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

// Dispatches to the non-virtual functions if OopClosureType has
// a concrete implementation, otherwise a virtual call is taken.
class Devirtualizer {
 public:
  template <typename OopClosureType, typename T> static void do_oop_no_verify(OopClosureType* closure, T* p);
  template <typename OopClosureType, typename T> static void do_oop(OopClosureType* closure, T* p);
  template <typename OopClosureType>             static void do_klass(OopClosureType* closure, Klass* k);
  template <typename OopClosureType>             static void do_cld(OopClosureType* closure, ClassLoaderData* cld);
  template <typename OopClosureType>             static bool do_metadata(OopClosureType* closure);
};

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