//----------------------------------------------------------------------
// Copyright 2007-2018 Cadence Design Systems, Inc.
// Copyright 2007-2011 Mentor Graphics Corporation
// Copyright 2010 AMD
// Copyright 2012-2018 NVIDIA Corporation
// Copyright 2014 Semifore
// Copyright 2012 Accellera Systems Initiative
// Copyright 2010-2014 Synopsys, Inc.
//   All Rights Reserved Worldwide
//
//   Licensed under the Apache License, Version 2.0 (the
//   "License"); you may not use this file except in
//   compliance with the License.  You may obtain a copy of
//   the License at
//
//       http://www.apache.org/licenses/LICENSE-2.0
//
//   Unless required by applicable law or agreed to in
//   writing, software distributed under the License is
//   distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
//   CONDITIONS OF ANY KIND, either express or implied.  See
//   the License for the specific language governing
//   permissions and limitations under the License.
//----------------------------------------------------------------------

`include "uvm_macros.svh"

//------------------------------------------------------------------------------
// Title: Callbacks Classes
//
// This section defines the classes used for callback registration, management,
// and user-defined callbacks.
//------------------------------------------------------------------------------

typedef class uvm_root;
typedef class uvm_callback;
typedef class uvm_callbacks_base;


//------------------------------------------------------------------------------
//
// Class - uvm_typeid_base
//
//------------------------------------------------------------------------------
//
// Simple typeid interface. Need this to set up the base-super mapping.
// This is similar to the factory, but much simpler. The idea of this
// interface is that each object type T has a typeid that can be
// used for mapping type relationships. This is not a user visible class.

class uvm_typeid_base;
  static string typename;
  static uvm_callbacks_base typeid_map[uvm_typeid_base];
  static uvm_typeid_base type_map[uvm_callbacks_base];
endclass


//------------------------------------------------------------------------------
//
// Class - uvm_typeid#(T)
//
//------------------------------------------------------------------------------

class uvm_typeid#(type T=uvm_object) extends uvm_typeid_base;
  static uvm_typeid#(T) m_b_inst;
  static function uvm_typeid#(T) get();
    if(m_b_inst == null)
      m_b_inst = new;
    return m_b_inst;
  endfunction
endclass

//------------------------------------------------------------------------------
// Class - uvm_callbacks_base
//
// Base class singleton that holds generic queues for all instance
// specific objects. This is an internal class. This class contains a
// global pool that has all of the instance specific callback queues in it. 
// All of the typewide callback queues live in the derivative class
// uvm_typed_callbacks#(T). This is not a user visible class.
//
// This class holds the class inheritance hierarchy information
// (super types and derivative types).
//
// Note, all derivative uvm_callbacks#() class singletons access this
// global m_pool object in order to get access to their specific
// instance queue.
//------------------------------------------------------------------------------

class uvm_callbacks_base extends uvm_object;

  typedef uvm_callbacks_base this_type;

  /*protected*/ static bit m_tracing = 1;
  static this_type m_b_inst;

  static uvm_pool#(uvm_object,uvm_queue#(uvm_callback)) m_pool;

  static function this_type m_initialize();
    if(m_b_inst == null) begin
      m_b_inst = new;
      m_pool = new;
    end
    return m_b_inst;
  endfunction

  //Type checking interface
  this_type       m_this_type[$];     //one to many T->T/CB
  uvm_typeid_base m_super_type;       //one to one relation 
  uvm_typeid_base m_derived_types[$]; //one to many relation

  virtual function bit m_am_i_a(uvm_object obj);
    return 0;
  endfunction

  virtual function bit m_is_for_me(uvm_callback cb);
    return 0;
  endfunction

  virtual function bit m_is_registered(uvm_object obj, uvm_callback cb);
    return 0;
  endfunction

  virtual function uvm_queue#(uvm_callback) m_get_tw_cb_q(uvm_object obj);
    return null;
  endfunction

  virtual function void m_add_tw_cbs(uvm_callback cb, uvm_apprepend ordering);
  endfunction

  virtual function bit m_delete_tw_cbs(uvm_callback cb);
    return 0;
  endfunction

  //Check registration. To test registration, start at this class and
  //work down the class hierarchy. If any class returns true then
  //the pair is legal.
  function bit check_registration(uvm_object obj, uvm_callback cb);
    this_type dt;

    if (m_is_registered(obj,cb))
      return 1;

    // Need to look at all possible T/CB pairs of this type
    foreach(m_this_type[i])
      if(m_b_inst != m_this_type[i] && m_this_type[i].m_is_registered(obj,cb))
        return 1;

    if(obj == null) begin
      foreach(m_derived_types[i]) begin
        dt = uvm_typeid_base::typeid_map[m_derived_types[i] ];
        if(dt != null && dt.check_registration(null,cb))
          return 1;
      end
    end

    return 0;
  endfunction

endclass


//------------------------------------------------------------------------------
//
// Class - uvm_typed_callbacks#(T)
//
//------------------------------------------------------------------------------
//
// Another internal class. This contains the queue of typewide
// callbacks. It also contains some of the public interface methods,
// but those methods are accessed via the uvm_callbacks#() class
// so they are documented in that class even though the implementation
// is in this class. 
//
// The <add>, <delete>, and <display> methods are implemented in this class.

class uvm_typed_callbacks#(type T=uvm_object) extends uvm_callbacks_base;

  static uvm_queue#(uvm_callback) m_tw_cb_q;
  static string m_typename;

  typedef uvm_typed_callbacks#(T) this_type;
  typedef uvm_callbacks_base      super_type;

  //The actual global object from the derivative class. Note that this is
  //just a reference to the object that is generated in the derived class.
  static this_type m_t_inst;

  static function this_type m_initialize();
    if(m_t_inst == null) begin
      void'(super_type::m_initialize());
      m_t_inst = new;
      m_t_inst.m_tw_cb_q = new("typewide_queue");
    end
    return m_t_inst;
  endfunction

  //Type checking interface: is given ~obj~ of type T?
  virtual function bit m_am_i_a(uvm_object obj);
    T this_type;
    if (obj == null)
      return 1;
    return($cast(this_type,obj));
  endfunction

  //Getting the typewide queue
  virtual function uvm_queue#(uvm_callback) m_get_tw_cb_q(uvm_object obj);
    if(m_am_i_a(obj)) begin
      foreach(m_derived_types[i]) begin
        super_type dt;
        dt = uvm_typeid_base::typeid_map[m_derived_types[i] ];
        if(dt != null && dt != this) begin
          m_get_tw_cb_q = dt.m_get_tw_cb_q(obj);
          if(m_get_tw_cb_q != null)
            return m_get_tw_cb_q;
        end
      end
      return m_t_inst.m_tw_cb_q;
    end
    else
      return null;
  endfunction

  static function int m_cb_find(uvm_queue#(uvm_callback) q, uvm_callback cb);
    for(int i=0; i<q.size(); ++i)
      if(q.get(i) == cb)
        return i;
    return -1;
  endfunction

  static function int m_cb_find_name(uvm_queue#(uvm_callback) q, string name, string where);
    uvm_callback cb;
    for(int i=0; i<q.size(); ++i) begin
      cb = q.get(i);
      if(cb.get_name() == name) begin
         `uvm_warning("UVM/CB/NAM/SAM", {"A callback named \"", name,
                                         "\" is already registered with ", where})
         return 1;
      end
    end
    return 0;
  endfunction

  //For a typewide callback, need to add to derivative types as well.
  virtual function void m_add_tw_cbs(uvm_callback cb, uvm_apprepend ordering);
    super_type cb_pair;
    uvm_object obj;
    T me;
    bit warned;
    uvm_queue#(uvm_callback) q;
    if(m_cb_find(m_t_inst.m_tw_cb_q,cb) == -1) begin
       warned = m_cb_find_name(m_t_inst.m_tw_cb_q, cb.get_name(), "type");
       if(ordering == UVM_APPEND)
          m_t_inst.m_tw_cb_q.push_back(cb);
       else
          m_t_inst.m_tw_cb_q.push_front(cb);
    end
    if(m_t_inst.m_pool.first(obj)) begin
      do begin
        if($cast(me,obj)) begin
          q = m_t_inst.m_pool.get(obj);
          if(q==null) begin
            q=new;
            m_t_inst.m_pool.add(obj,q);
          end
          if(m_cb_find(q,cb) == -1) begin
            if (!warned) begin
               void'(m_cb_find_name(q, cb.get_name(), {"object instance ", me.get_full_name()}));
            end
            if(ordering == UVM_APPEND)
              q.push_back(cb);
            else
              q.push_front(cb);
          end
        end
      end while(m_t_inst.m_pool.next(obj));
    end
    foreach(m_derived_types[i]) begin
      cb_pair = uvm_typeid_base::typeid_map[m_derived_types[i] ];
      if(cb_pair != this)
        cb_pair.m_add_tw_cbs(cb,ordering);
    end
  endfunction


  //For a typewide callback, need to remove from derivative types as well.
  virtual function bit m_delete_tw_cbs(uvm_callback cb);
    super_type cb_pair;
    uvm_object obj;
    uvm_queue#(uvm_callback) q;
    int pos = m_cb_find(m_t_inst.m_tw_cb_q,cb);

    if(pos != -1) begin
      m_t_inst.m_tw_cb_q.delete(pos);
      m_delete_tw_cbs = 1;
    end

    if(m_t_inst.m_pool.first(obj)) begin
      do begin
        q = m_t_inst.m_pool.get(obj);
        if(q==null) begin
          q=new;
          m_t_inst.m_pool.add(obj,q);
        end
        pos = m_cb_find(q,cb);
        if(pos != -1) begin
          q.delete(pos);
          m_delete_tw_cbs = 1;
        end
      end while(m_t_inst.m_pool.next(obj));
    end
    foreach(m_derived_types[i]) begin
      cb_pair = uvm_typeid_base::typeid_map[m_derived_types[i] ];
      if(cb_pair != this)
        m_delete_tw_cbs |= cb_pair.m_delete_tw_cbs(cb);
    end
  endfunction


  static function void display(T obj=null);
    T me;
    string cbq[$];
    string inst_q[$];
    string mode_q[$];
    uvm_callback cb;
    string blanks = "                             ";
    uvm_object bobj = obj;
    string qs[$];

    uvm_queue#(uvm_callback) q;
    string tname, str;

    int max_cb_name=0, max_inst_name=0;

    m_tracing = 0; //don't allow tracing during display

    if(m_typename != "") tname = m_typename;
    else if(obj != null) tname = obj.get_type_name();
    else tname = "*";

    q = m_t_inst.m_tw_cb_q;
    for(int i=0; i<q.size(); ++i) begin
      cb = q.get(i);
      cbq.push_back(cb.get_name());
      inst_q.push_back("(*)");
      if(cb.is_enabled()) mode_q.push_back("ON");
      else mode_q.push_back("OFF");

      str = cb.get_name();
      max_cb_name = max_cb_name > str.len() ? max_cb_name : str.len();
      str = "(*)";
      max_inst_name = max_inst_name > str.len() ? max_inst_name : str.len();
    end

    if(obj ==null) begin
      if(m_t_inst.m_pool.first(bobj)) begin
        do
          if($cast(me,bobj)) break;
        while(m_t_inst.m_pool.next(bobj));
      end
      if(me != null || m_t_inst.m_tw_cb_q.size()) begin
        qs.push_back($sformatf("Registered callbacks for all instances of %s\n", tname)); 
        qs.push_back("---------------------------------------------------------------\n");
      end
      if(me != null) begin
        do begin
          if($cast(me,bobj)) begin
            q = m_t_inst.m_pool.get(bobj);
            if (q==null) begin
              q=new;
              m_t_inst.m_pool.add(bobj,q);
            end
            for(int i=0; i<q.size(); ++i) begin
              cb = q.get(i);
              cbq.push_back(cb.get_name());
              inst_q.push_back(bobj.get_full_name());
              if(cb.is_enabled()) mode_q.push_back("ON");
              else mode_q.push_back("OFF");
  
              str = cb.get_name();
              max_cb_name = max_cb_name > str.len() ? max_cb_name : str.len();
              str = bobj.get_full_name();
              max_inst_name = max_inst_name > str.len() ? max_inst_name : str.len();
            end
          end
        end while (m_t_inst.m_pool.next(bobj));
      end
      else begin
        qs.push_back($sformatf("No callbacks registered for any instances of type %s\n", tname));
      end
    end
    else begin
      if(m_t_inst.m_pool.exists(bobj) || m_t_inst.m_tw_cb_q.size()) begin
       qs.push_back($sformatf("Registered callbacks for instance %s of %s\n", obj.get_full_name(), tname)); 
       qs.push_back("---------------------------------------------------------------\n");
      end
      if(m_t_inst.m_pool.exists(bobj)) begin
        q = m_t_inst.m_pool.get(bobj);
        if(q==null) begin
          q=new;
          m_t_inst.m_pool.add(bobj,q);
        end
        for(int i=0; i<q.size(); ++i) begin
          cb = q.get(i);
          cbq.push_back(cb.get_name());
          inst_q.push_back(bobj.get_full_name());
          if(cb.is_enabled()) mode_q.push_back("ON");
          else mode_q.push_back("OFF");

          str = cb.get_name();
          max_cb_name = max_cb_name > str.len() ? max_cb_name : str.len();
          str = bobj.get_full_name();
          max_inst_name = max_inst_name > str.len() ? max_inst_name : str.len();
        end
      end
    end
    if(!cbq.size()) begin
      if(obj == null) str = "*";
      else str = obj.get_full_name();
      qs.push_back($sformatf("No callbacks registered for instance %s of type %s\n", str, tname));
    end

    foreach (cbq[i]) begin
      qs.push_back($sformatf("%s  %s %s on %s  %s\n", cbq[i], blanks.substr(0,max_cb_name-cbq[i].len()-1), inst_q[i], blanks.substr(0,max_inst_name - inst_q[i].len()-1), mode_q[i]));
    end
    `uvm_info("UVM/CB/DISPLAY",`UVM_STRING_QUEUE_STREAMING_PACK(qs),UVM_NONE)

    m_tracing = 1; //allow tracing to be resumed
  endfunction

endclass


//------------------------------------------------------------------------------
//
// CLASS -- NODOCS -- uvm_callbacks #(T,CB)
//
// The ~uvm_callbacks~ class provides a base class for implementing callbacks,
// which are typically used to modify or augment component behavior without
// changing the component class. To work effectively, the developer of the
// component class defines a set of "hook" methods that enable users to
// customize certain behaviors of the component in a manner that is controlled
// by the component developer. The integrity of the component's overall behavior
// is intact, while still allowing certain customizable actions by the user.
// 
// To enable compile-time type-safety, the class is parameterized on both the
// user-defined callback interface implementation as well as the object type
// associated with the callback. The object type-callback type pair are
// associated together using the <`uvm_register_cb> macro to define
// a valid pairing; valid pairings are checked when a user attempts to add
// a callback to an object.
//
// To provide the most flexibility for end-user customization and reuse, it
// is recommended that the component developer also define a corresponding set
// of virtual method hooks in the component itself. This affords users the ability
// to customize via inheritance/factory overrides as well as callback object
// registration. The implementation of each virtual method would provide the
// default traversal algorithm for the particular callback being called. Being
// virtual, users can define subtypes that override the default algorithm,
// perform tasks before and/or after calling super.<method> to execute any
// registered callbacks, or to not call the base implementation, effectively
// disabling that particular hook. A demonstration of this methodology is
// provided in an example included in the kit.
//------------------------------------------------------------------------------

// Class: uvm_callbacks#(T, CB)
// Implementation of uvm_callbacks#(T,CB) class, as defined in
// section 10.7.2.1.
//
// | class uvm_callbacks #(type T=uvm_object, type CB=uvm_callback)
//
  
// @uvm-ieee 1800.2-2017 auto 10.7.2.1
class uvm_callbacks #(type T=uvm_object, type CB=uvm_callback)
    extends uvm_typed_callbacks#(T);

  // Parameter -- NODOCS -- T
  //
  // This type parameter specifies the base object type with which the
  // <CB> callback objects will be registered. This object must be
  // a derivative of ~uvm_object~.

  // Parameter -- NODOCS -- CB
  //
  // This type parameter specifies the base callback type that will be
  // managed by this callback class. The callback type is typically a
  // interface class, which defines one or more virtual method prototypes 
  // that users can override in subtypes. This type must be a derivative
  // of <uvm_callback>.
  
  typedef uvm_typed_callbacks#(T) super_type;
  typedef uvm_callbacks#(T,CB) this_type;


  // Singleton instance is used for type checking
  local static this_type m_inst;

  // typeinfo
  static uvm_typeid_base m_typeid;
  static uvm_typeid_base m_cb_typeid;

  static string m_typename;
  static string m_cb_typename;
  static uvm_callbacks#(T,uvm_callback) m_base_inst;

  bit m_registered;

  // get
  // ---

  static function this_type get();

    if (m_inst == null) begin
      uvm_typeid_base cb_base_type;

      void'(super_type::m_initialize());
    
      cb_base_type = uvm_typeid#(uvm_callback)::get();
      m_cb_typeid  = uvm_typeid#(CB)::get();
      m_typeid     = uvm_typeid#(T)::get();

      m_inst = new;

      if (cb_base_type == m_cb_typeid) begin
        $cast(m_base_inst, m_inst);
        // The base inst in the super class gets set to this base inst
        m_t_inst = m_base_inst;
        uvm_typeid_base::typeid_map[m_typeid] = m_inst; 
        uvm_typeid_base::type_map[m_b_inst] = m_typeid;
      end
      else begin
        m_base_inst = uvm_callbacks#(T,uvm_callback)::get();
        m_base_inst.m_this_type.push_back(m_inst);
      end

      if (m_inst == null)
        `uvm_fatal("CB/INTERNAL","get(): m_inst is null")
    end

    return m_inst;
  endfunction


  // m_register_pair
  // -------------
  // Register valid callback type

  static function bit m_register_pair(string tname="", cbname="");
    this_type inst = get();

    m_typename = tname;
    super_type::m_typename = tname;
    m_typeid.typename = tname;

    m_cb_typename = cbname;
    m_cb_typeid.typename = cbname;

    inst.m_registered = 1; 

    return 1;
  endfunction

  virtual function bit m_is_registered(uvm_object obj, uvm_callback cb);
    if(m_is_for_me(cb) && m_am_i_a(obj)) begin
      return m_registered;
    end
  endfunction

  //Does type check to see if the callback is valid for this type
  virtual function bit m_is_for_me(uvm_callback cb);
    CB this_cb;
    return($cast(this_cb,cb));
  endfunction

  // Group -- NODOCS -- Add/delete interface

  // Function -- NODOCS -- add
  //
  // Registers the given callback object, ~cb~, with the given
  // ~obj~ handle. The ~obj~ handle can be ~null~, which allows 
  // registration of callbacks without an object context. If
  // ~ordering~ is UVM_APPEND (default), the callback will be executed
  // after previously added callbacks, else  the callback
  // will be executed ahead of previously added callbacks. The ~cb~
  // is the callback handle; it must be non-~null~, and if the callback
  // has already been added to the object instance then a warning is
  // issued. Note that the CB parameter is optional. For example, the 
  // following are equivalent:
  //
  //| uvm_callbacks#(my_comp)::add(comp_a, cb);
  //| uvm_callbacks#(my_comp, my_callback)::add(comp_a,cb);

  // @uvm-ieee 1800.2-2017 auto 10.7.2.3.1
  static function void add(T obj, uvm_callback cb, uvm_apprepend ordering=UVM_APPEND);
    uvm_queue#(uvm_callback) q;
    string nm,tnm; 

    void'(get());

    if (cb==null) begin
       if (obj==null)
         nm = "(*)";
       else
         nm = obj.get_full_name();

       if (m_base_inst.m_typename!="")
         tnm = m_base_inst.m_typename;
       else if (obj != null)
         tnm = obj.get_type_name();
       else
         tnm = "uvm_object";

       uvm_report_error("CBUNREG",
                       {"Null callback object cannot be registered with object ",
                        nm, " (", tnm, ")"}, UVM_NONE);
       return;
    end

    if (!m_base_inst.check_registration(obj,cb)) begin

       if (obj==null)
         nm = "(*)";
       else
         nm = obj.get_full_name();

       if (m_base_inst.m_typename!="")
         tnm = m_base_inst.m_typename;
       else if(obj != null)
         tnm = obj.get_type_name();
       else
         tnm = "uvm_object";

       uvm_report_warning("CBUNREG",
                          {"Callback ", cb.get_name(), " cannot be registered with object ",
                          nm, " because callback type ", cb.get_type_name(),
                          " is not registered with object type ", tnm }, UVM_NONE);
    end

    if(obj == null) begin

      if (m_cb_find(m_t_inst.m_tw_cb_q,cb) != -1) begin

        if (m_base_inst.m_typename!="")
          tnm = m_base_inst.m_typename;
        else tnm = "uvm_object";

        uvm_report_warning("CBPREG",
                           {"Callback object ", cb.get_name(),
                           " is already registered with type ", tnm }, UVM_NONE);
      end
      else begin
        `uvm_cb_trace_noobj(cb,$sformatf("Add (%s) typewide callback %0s for type %s",
                            ordering.name(), cb.get_name(), m_base_inst.m_typename))
        m_t_inst.m_add_tw_cbs(cb,ordering);
      end
    end

    else begin

      `uvm_cb_trace_noobj(cb,$sformatf("Add (%s) callback %0s to object %0s ",
                          ordering.name(), cb.get_name(), obj.get_full_name()))

      q = m_base_inst.m_pool.get(obj);

      if (q==null) begin
        q=new;
        m_base_inst.m_pool.add(obj,q);
      end

      if(q.size() == 0) begin
        // Need to make sure that registered report catchers are added. This
        // way users don't need to set up uvm_report_object as a super type.
        uvm_report_object o; 

        if($cast(o,obj)) begin
          uvm_queue#(uvm_callback) qr;
	  void'(uvm_callbacks#(uvm_report_object, uvm_callback)::get());
          qr = uvm_callbacks#(uvm_report_object,uvm_callback)::m_t_inst.m_tw_cb_q;
          for(int i=0; i<qr.size(); ++i)
              q.push_back(qr.get(i)); 
        end

        for(int i=0; i<m_t_inst.m_tw_cb_q.size(); ++i)
          q.push_back(m_t_inst.m_tw_cb_q.get(i)); 
      end

      //check if already exists in the queue
      if(m_cb_find(q,cb) != -1) begin
        uvm_report_warning("CBPREG", { "Callback object ", cb.get_name(), " is already registered",
                           " with object ", obj.get_full_name() }, UVM_NONE);
      end
      else begin
        void'(m_cb_find_name(q, cb.get_name(), {"object instance ", obj.get_full_name()}));
        if(ordering == UVM_APPEND)
          q.push_back(cb);
        else
          q.push_front(cb);
      end
    end
  endfunction

  // Function -- NODOCS -- add_by_name
  //
  // Registers the given callback object, ~cb~, with one or more uvm_components.
  // The components must already exist and must be type T or a derivative. As
  // with <add> the CB parameter is optional. ~root~ specifies the location in
  // the component hierarchy to start the search for ~name~. See <uvm_root::find_all>
  // for more details on searching by name.

  // @uvm-ieee 1800.2-2017 auto 10.7.2.3.2
  static function void add_by_name(string name,
                                   uvm_callback cb,
                                   uvm_component root,
                                   uvm_apprepend ordering=UVM_APPEND);
    uvm_component cq[$];
    uvm_root top;
    uvm_coreservice_t cs;
    T t;
    void'(get());
    cs = uvm_coreservice_t::get();
    top = cs.get_root();

    if(cb==null) begin
       uvm_report_error("CBUNREG", { "Null callback object cannot be registered with object(s) ",
         name }, UVM_NONE);
       return;
    end
    `uvm_cb_trace_noobj(cb,$sformatf("Add (%s) callback %0s by name to object(s) %0s ",
                    ordering.name(), cb.get_name(), name))
    top.find_all(name,cq,root);
    if(cq.size() == 0) begin
      uvm_report_warning("CBNOMTC", { "add_by_name failed to find any components matching the name ",
        name, ", callback ", cb.get_name(), " will not be registered." }, UVM_NONE);
    end
    foreach(cq[i]) begin
      if($cast(t,cq[i])) begin 
        add(t,cb,ordering); 
      end
    end
  endfunction


  // Function -- NODOCS -- delete
  //
  // Deletes the given callback object, ~cb~, from the queue associated with
  //  the given ~obj~ handle. The ~obj~ handle can be ~null~, which allows
  // de-registration of callbacks without an object context. 
  // The ~cb~ is the callback handle; it must be non-~null~, and if the callback
  // has already been removed from the object instance then a warning is
  // issued. Note that the CB parameter is optional. For example, the 
  // following are equivalent:
  //
  //| uvm_callbacks#(my_comp)::delete(comp_a, cb);
  //| uvm_callbacks#(my_comp, my_callback)::delete(comp_a,cb);

  // @uvm-ieee 1800.2-2017 auto 10.7.2.3.3
  static function void delete(T obj, uvm_callback cb);
    uvm_object b_obj = obj;
    uvm_queue#(uvm_callback) q;
    bit found;
    int pos;
    void'(get());

    if(obj == null) begin
      `uvm_cb_trace_noobj(cb,$sformatf("Delete typewide callback %0s for type %s",
                       cb.get_name(), m_base_inst.m_typename))
      found = m_t_inst.m_delete_tw_cbs(cb);
    end
    else begin
      `uvm_cb_trace_noobj(cb,$sformatf("Delete callback %0s from object %0s ",
                      cb.get_name(), obj.get_full_name()))
      q = m_base_inst.m_pool.get(b_obj);
      pos = m_cb_find(q,cb);
      if(pos != -1) begin
        q.delete(pos);
        found = 1;
      end
    end
    if(!found) begin
      string nm;
      if(obj==null) nm = "(*)"; else nm = obj.get_full_name();
      uvm_report_warning("CBUNREG", { "Callback ", cb.get_name(), " cannot be removed from object ",
        nm, " because it is not currently registered to that object." }, UVM_NONE);
    end
  endfunction


  // Function -- NODOCS -- delete_by_name
  //
  // Removes the given callback object, ~cb~, associated with one or more 
  // uvm_component callback queues. As with <delete> the CB parameter is 
  // optional. ~root~ specifies the location in the component hierarchy to start 
  // the search for ~name~. See <uvm_root::find_all> for more details on searching 
  // by name.

  // @uvm-ieee 1800.2-2017 auto 10.7.2.3.4
  static function void delete_by_name(string name, uvm_callback cb,
     uvm_component root);
    uvm_component cq[$];
    uvm_root top;
    T t;
    uvm_coreservice_t cs;
    void'(get());
    cs = uvm_coreservice_t::get();
    top = cs.get_root();

    `uvm_cb_trace_noobj(cb,$sformatf("Delete callback %0s by name from object(s) %0s ",
                    cb.get_name(), name))
    top.find_all(name,cq,root);
    if(cq.size() == 0) begin
      uvm_report_warning("CBNOMTC", { "delete_by_name failed to find any components matching the name ",
        name, ", callback ", cb.get_name(), " will not be unregistered." }, UVM_NONE);
    end
    foreach(cq[i]) begin
      if($cast(t,cq[i])) begin 
        delete(t,cb); 
      end
    end
  endfunction

  //--------------------------
  // Group -- NODOCS -- Iterator Interface
  //--------------------------
  //
  // This set of functions provide an iterator interface for callback queues. A facade
  // class, <uvm_callback_iter> is also available, and is the generally preferred way to
  // iterate over callback queues.

  static function void m_get_q (ref uvm_queue #(uvm_callback) q, input T obj);
    if(!m_base_inst.m_pool.exists(obj)) begin //no instance specific
      q = (obj == null) ? m_t_inst.m_tw_cb_q : m_t_inst.m_get_tw_cb_q(obj);
    end 
    else begin
      q = m_base_inst.m_pool.get(obj);
      if(q==null) begin
        q=new;
        m_base_inst.m_pool.add(obj,q);
      end
    end
  endfunction


  // Function -- NODOCS -- get_first
  //
  // Returns the first enabled callback of type CB which resides in the queue for ~obj~.
  // If ~obj~ is ~null~ then the typewide queue for T is searched. ~itr~ is the iterator;
  // it will be updated with a value that can be supplied to <get_next> to get the next
  // callback object.
  //
  // If the queue is empty then ~null~ is returned. 
  //
  // The iterator class <uvm_callback_iter> may be used as an alternative, simplified,
  // iterator interface.

  // @uvm-ieee 1800.2-2017 auto 10.7.2.4.1
  static function CB get_first (ref int itr, input T obj);
    uvm_queue#(uvm_callback) q;
    CB cb;
    void'(get());
    m_get_q(q,obj);
    for(itr = 0; itr<q.size(); ++itr)
      if($cast(cb, q.get(itr)) && cb.callback_mode())
         return cb;
    return null;
  endfunction

  // Function -- NODOCS -- get_last
  //
  // Returns the last enabled callback of type CB which resides in the queue for ~obj~.
  // If ~obj~ is ~null~ then the typewide queue for T is searched. ~itr~ is the iterator;
  // it will be updated with a value that can be supplied to <get_prev> to get the previous
  // callback object.
  //
  // If the queue is empty then ~null~ is returned.
  //
  // The iterator class <uvm_callback_iter> may be used as an alternative, simplified,
  // iterator interface.

  // @uvm-ieee 1800.2-2017 auto 10.7.2.4.2
  static function CB get_last (ref int itr, input T obj);
    uvm_queue#(uvm_callback) q;
    CB cb;
    void'(get());
    m_get_q(q,obj);
    for(itr = q.size()-1; itr>=0; --itr)
      if ($cast(cb, q.get(itr)) && cb.callback_mode())
         return cb;
    return null;
  endfunction


  // Function -- NODOCS -- get_next
  //
  // Returns the next enabled callback of type CB which resides in the queue for ~obj~,
  // using ~itr~ as the starting point. If ~obj~ is ~null~ then the typewide queue for T
  // is searched. ~itr~ is the iterator; it will be updated with a value that can be 
  // supplied to <get_next> to get the next callback object.
  //
  // If no more callbacks exist in the queue, then ~null~ is returned. <get_next> will
  // continue to return ~null~ in this case until <get_first> or <get_last> has been used to reset
  // the iterator.
  //
  // The iterator class <uvm_callback_iter> may be used as an alternative, simplified,
  // iterator interface.

  // @uvm-ieee 1800.2-2017 auto 10.7.2.4.3
  static function CB get_next (ref int itr, input T obj);
    uvm_queue#(uvm_callback) q;
    CB cb;
    void'(get());
    m_get_q(q,obj);
    for(itr = itr+1; itr<q.size(); ++itr)
      if ($cast(cb, q.get(itr)) && cb.callback_mode())
         return cb;
    return null;
  endfunction


  // Function -- NODOCS -- get_prev
  //
  // Returns the previous enabled callback of type CB which resides in the queue for ~obj~,
  // using ~itr~ as the starting point. If ~obj~ is ~null~ then the typewide queue for T
  // is searched. ~itr~ is the iterator; it will be updated with a value that can be 
  // supplied to <get_prev> to get the previous callback object.
  //
  // If no more callbacks exist in the queue, then ~null~ is returned. <get_prev> will
  // continue to return ~null~ in this case until <get_first> or <get_last> has been used to reset
  // the iterator.
  //
  // The iterator class <uvm_callback_iter> may be used as an alternative, simplified,
  // iterator interface.

  // @uvm-ieee 1800.2-2017 auto 10.7.2.4.4
  static function CB get_prev (ref int itr, input T obj);
    uvm_queue#(uvm_callback) q;
    CB cb;
    void'(get());
    m_get_q(q,obj);
    for(itr = itr-1; itr>= 0; --itr)
      if($cast(cb, q.get(itr)) && cb.callback_mode())
         return cb;
    return null;
  endfunction


  // Function: get_all
  // Populates the end of the ~all_callbacks~ queue with the list of all registered callbacks
  // for ~obj~ (whether they are enabled or disabled).
  //
  // If ~obj~ is ~null~, then ~all_callbacks~ shall be populated with all registered typewide
  // callbacks.  If ~obj~ is not ~null~, then ~all_callbacks~ shall be populated with both
  // the typewide and instance callbacks (if any) registered for ~obj~.
  //
  // NOTE: This API contradicts the definition provided in section 10.7.2.5 of the P1800.2-2017
  //       LRM.  See DEVIATIONS.md for additional details.
  //
  //| static function void get_all( ref CB all_callbacks[$], input T obj=null );
  //
  // @uvm-contrib This API is being considered for potential contribution to 1800.2

  // @uvm-ieee 1800.2-2017 auto 10.7.2.5
  static function void get_all ( ref CB all_callbacks[$], input T obj=null );
    uvm_queue#(uvm_callback) q;
    CB cb;
    CB callbacks_to_append[$];
    CB unique_callbacks_to_append[$];

    void'( get() );

    if ((obj == null) || (!m_pool.exists(obj))) begin
      // Only typewide callbacks exist
      for (int qi=0; qi<m_t_inst.m_tw_cb_q.size(); ++qi) 
	if ($cast(cb, m_t_inst.m_tw_cb_q.get(qi)))
	  callbacks_to_append.push_back( cb );
    end
    else begin
      // No need to do anything special with typewide,
      // as they're present in the instance queue.
      q = m_pool.get(obj);
      for (int qi=0; qi < q.size(); qi++)
	if ($cast(cb, q.get( qi )))
	  callbacks_to_append.push_back( cb );
    end

    // Now remove duplicates and append the final list to all_callbacks.
    unique_callbacks_to_append = callbacks_to_append.unique( cb_ ) with ( cb_.get_inst_id );
    all_callbacks = { all_callbacks, unique_callbacks_to_append };
  endfunction


  //-------------
  // Group -- NODOCS -- Debug
  //-------------

  // Function -- NODOCS -- display
  //
  // This function displays callback information for ~obj~. If ~obj~ is
  // ~null~, then it displays callback information for all objects
  // of type ~T~, including typewide callbacks.

  static function void display(T obj=null);
    // For documentation purposes, need a function wrapper here.
    void'(get());
    super_type::display(obj);
  endfunction

endclass


//------------------------------------------------------------------------------
//
// Class- uvm_derived_callbacks #(T,ST,CB)
//
//------------------------------------------------------------------------------
// This type is not really expected to be used directly by the user, instead they are 
// expected to use the macro `uvm_set_super_type. The sole purpose of this type is to
// allow for setting up of the derived_type/super_type mapping.
//------------------------------------------------------------------------------

class uvm_derived_callbacks#(type T=uvm_object, type ST=uvm_object, type CB=uvm_callback)
    extends uvm_callbacks#(T,CB);

  typedef uvm_derived_callbacks#(T,ST,CB) this_type;
  typedef uvm_callbacks#(T)            this_user_type;
  typedef uvm_callbacks#(ST)           this_super_type;
 
  // Singleton instance is used for type checking
  static this_type m_d_inst;
  static this_user_type m_user_inst;
  static this_super_type m_super_inst;

  // typeinfo
  static uvm_typeid_base m_s_typeid;

  static function this_type get();
    m_user_inst = this_user_type::get();
    m_super_inst = this_super_type::get();
    m_s_typeid = uvm_typeid#(ST)::get();
    if(m_d_inst == null) begin
      m_d_inst = new;
    end
    return m_d_inst;
  endfunction

  static function bit register_super_type(string tname="", sname="");
    this_user_type u_inst = this_user_type::get();
    uvm_callbacks_base s_obj;

    void'(this_type::get()); // make sure it exists
    this_user_type::m_t_inst.m_typename = tname;

    if(sname != "") m_s_typeid.typename = sname;

    if(u_inst.m_super_type != null) begin
      if(u_inst.m_super_type == m_s_typeid) return 1;
      uvm_report_warning("CBTPREG", { "Type ", tname, " is already registered to super type ", 
        this_super_type::m_t_inst.m_typename, ". Ignoring attempt to register to super type ",
        sname}, UVM_NONE); 
      return 1;
    end
    if(this_super_type::m_t_inst.m_typename == "")
      this_super_type::m_t_inst.m_typename = sname;
    u_inst.m_super_type = m_s_typeid;
    u_inst.m_base_inst.m_super_type = m_s_typeid;
    s_obj = uvm_typeid_base::typeid_map[m_s_typeid];
    s_obj.m_derived_types.push_back(m_typeid);
    return 1;
  endfunction

endclass


//------------------------------------------------------------------------------
//
// CLASS -- NODOCS -- uvm_callback_iter
//
//------------------------------------------------------------------------------
// The ~uvm_callback_iter~ class is an iterator class for iterating over
// callback queues of a specific callback type. The typical usage of
// the class is:
//
//| uvm_callback_iter#(mycomp,mycb) iter = new(this);
//| for(mycb cb = iter.first(); cb != null; cb = iter.next())
//|    cb.dosomething();
//
// The callback iteration macros, <`uvm_do_callbacks> and
// <`uvm_do_callbacks_exit_on> provide a simple method for iterating
// callbacks and executing the callback methods.
//------------------------------------------------------------------------------

// @uvm-ieee 1800.2-2017 auto D.1.1
class uvm_callback_iter#(type T = uvm_object, type CB = uvm_callback);

   local int m_i;
   local T   m_obj;
   local CB  m_cb;

   // Function -- NODOCS -- new
   //
   // Creates a new callback iterator object. It is required that the object
   // context be provided.

   // @uvm-ieee 1800.2-2017 auto D.1.2.1
   function new(T obj);
      m_obj = obj;
   endfunction

   // Function -- NODOCS -- first
   //
   // Returns the first valid (enabled) callback of the callback type (or
   // a derivative) that is in the queue of the context object. If the
   // queue is empty then ~null~ is returned.

   // @uvm-ieee 1800.2-2017 auto D.1.2.2
   function CB first();
      m_cb = uvm_callbacks#(T,CB)::get_first(m_i, m_obj);
      return m_cb;
   endfunction

   // Function -- NODOCS -- last
   //
   // Returns the last valid (enabled) callback of the callback type (or
   // a derivative) that is in the queue of the context object. If the
   // queue is empty then ~null~ is returned.

   // @uvm-ieee 1800.2-2017 auto D.1.2.3
   function CB last();
      m_cb = uvm_callbacks#(T,CB)::get_last(m_i, m_obj);
      return m_cb;
   endfunction

   // Function -- NODOCS -- next
   //
   // Returns the next valid (enabled) callback of the callback type (or
   // a derivative) that is in the queue of the context object. If there
   // are no more valid callbacks in the queue, then ~null~ is returned.

   // @uvm-ieee 1800.2-2017 auto D.1.2.4
   function CB next();
      m_cb = uvm_callbacks#(T,CB)::get_next(m_i, m_obj);
      return m_cb;
   endfunction

   // Function -- NODOCS -- prev
   //
   // Returns the previous valid (enabled) callback of the callback type (or
   // a derivative) that is in the queue of the context object. If there
   // are no more valid callbacks in the queue, then ~null~ is returned.

   // @uvm-ieee 1800.2-2017 auto D.1.2.5
   function CB prev();
      m_cb = uvm_callbacks#(T,CB)::get_prev(m_i, m_obj);
      return m_cb;
   endfunction

   // Function -- NODOCS -- get_cb
   //
   // Returns the last callback accessed via a first() or next()
   // call. 

   // @uvm-ieee 1800.2-2017 auto D.1.2.6
   function CB get_cb();
      return m_cb;
   endfunction

/****
   function void trace(uvm_object obj = null);
      if (m_cb != null && T::cbs::get_debug_flags() & UVM_CALLBACK_TRACE) begin
         uvm_report_object reporter = null;
         string who = "Executing ";
         void'($cast(reporter, obj));
         if (reporter == null) void'($cast(reporter, m_obj));
         if (reporter == null) reporter = uvm_top;
         if (obj != null) who = {obj.get_full_name(), " is executing "};
         else if (m_obj != null) who = {m_obj.get_full_name(), " is executing "};
         reporter.uvm_report_info("CLLBK_TRC", {who, "callback ", m_cb.get_name()}, UVM_LOW);
      end
   endfunction
****/
endclass


//------------------------------------------------------------------------------
// CLASS -- NODOCS -- uvm_callback
//
// The ~uvm_callback~ class is the base class for user-defined callback classes.
// Typically, the component developer defines an application-specific callback
// class that extends from this class. In it, he defines one or more virtual
// methods, called a ~callback interface~, that represent the hooks available
// for user override. 
//
// Methods intended for optional override should not be declared ~pure.~ Usually,
// all the callback methods are defined with empty implementations so users have
// the option of overriding any or all of them.
//
// The prototypes for each hook method are completely application specific with
// no restrictions.
//------------------------------------------------------------------------------

// @uvm-ieee 1800.2-2017 auto 10.7.1.1
class uvm_callback extends uvm_object;
  protected bit m_enabled = 1;

  `uvm_object_utils(uvm_callback)
  
  // Function -- NODOCS -- new
  //
  // Creates a new uvm_callback object, giving it an optional ~name~.

  // @uvm-ieee 1800.2-2017 auto 10.7.1.2.1
  function new(string name="uvm_callback");
    super.new(name);
  endfunction


  // Function -- NODOCS -- callback_mode
  //
  // Enable/disable callbacks (modeled like rand_mode and constraint_mode).

  // @uvm-ieee 1800.2-2017 auto 10.7.1.2.2
  function bit callback_mode(int on=-1);
    if(on == 0 || on == 1) begin
      `uvm_cb_trace_noobj(this,$sformatf("Setting callback mode for %s to %s",
            get_name(), ((on==1) ? "ENABLED":"DISABLED")))
    end
    else begin
      `uvm_cb_trace_noobj(this,$sformatf("Callback mode for %s is %s",
            get_name(), ((m_enabled==1) ? "ENABLED":"DISABLED")))
    end
    callback_mode = m_enabled;
    if(on==0) m_enabled=0;
    if(on==1) m_enabled=1;
  endfunction


  // Function -- NODOCS -- is_enabled
  //
  // Returns 1 if the callback is enabled, 0 otherwise.

  // @uvm-ieee 1800.2-2017 auto 10.7.1.2.3
  function bit is_enabled();
    return callback_mode();
  endfunction

endclass