transfer.h

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/*
 * Copyright 2025 Stanford University, NVIDIA Corporation
 * SPDX-License-Identifier: Apache-2.0
 *
 * 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.
 */
 
// data transfer (a.k.a. dma) engine for Realm
 
#ifndef REALM_TRANSFER_H
#define REALM_TRANSFER_H
 
#include "realm/bgwork.h"
#include "realm/event.h"
#include "realm/memory.h"
#include "realm/indexspace.h"
#include "realm/inst_impl.h"
#include "realm/atomics.h"
#include "realm/network.h"
#include "realm/operation.h"
#include "realm/transfer/address_list.h"
#include "realm/transfer/channel.h"
#include "realm/profiling.h"
 
namespace Realm {
 
  // the data transfer engine has too much code to have it all be templated on the
  //  type of IndexSpace that is driving the transfer, so we need a widget that
  //  can hold an arbitrary IndexSpace and dispatch based on its type
 
  struct Node;
  class XferDes;
  class AddressList;
 
  class TransferIterator {
  public:
    template <typename S>
    static TransferIterator *deserialize_new(S &deserializer);
 
    virtual ~TransferIterator(void);
 
    // must be called (and waited on) before iteration is possible
    virtual Event request_metadata(void);
 
    // specify the xd port used for indirect address flow control, if any
    virtual void set_indirect_input_port(XferDes *xd, int port_idx,
                                         TransferIterator *inner_iter);
 
    virtual void reset(void) = 0;
    virtual bool done(void) = 0;
    virtual size_t get_base_offset(void) const;
    virtual size_t get_address_size(void) const;
 
    // flag bits to control iterators
    enum
    {
      SRC_PARTIAL_OK = (1 << 0),
      SRC_LINES_OK = (1 << 1),
      SRC_PLANES_OK = (1 << 2),
      SRC_FLAGMASK = 0xff,
 
      DST_PARTIAL_OK = (1 << 8),
      DST_LINES_OK = (1 << 9),
      DST_PLANES_OK = (1 << 10),
      DST_FLAGMASK = 0xff00,
 
      PARTIAL_OK = SRC_PARTIAL_OK | DST_PARTIAL_OK,
      LINES_OK = SRC_LINES_OK | DST_LINES_OK,
      PLANES_OK = SRC_PLANES_OK | DST_PLANES_OK,
    };
 
    struct AddressInfo {
      size_t base_offset;
      size_t bytes_per_chunk; // multiple of sizeof(T) unless PARTIAL_OK
      size_t num_lines;       // guaranteed to be 1 unless LINES_OK (i.e. 2D)
      size_t line_stride;
      size_t num_planes; // guaranteed to be 1 unless PLANES_OK (i.e. 3D)
      size_t plane_stride;
    };
 
    // a custom address info interface for cases where linearized
    //  addresses are not suitable
    class AddressInfoCustom {
    protected:
      virtual ~AddressInfoCustom() {}
 
    public:
      // offers an N-D rectangle from a given piece of a given instance,
      //  along with a specified dimension order
      // return value is how many dimensions are accepted (0 = single
      //  point), which can be less than the input if the target has
      //  strict ordering rules
      virtual int set_rect(const RegionInstanceImpl *inst,
                           const InstanceLayoutPieceBase *piece, size_t field_size,
                           size_t field_offset, int ndims, const int64_t lo[/*ndims*/],
                           const int64_t hi[/*ndims*/], const int order[/*ndims*/]) = 0;
    };
 
    // if a step is tentative, it must either be confirmed or cancelled before
    //  another one is possible
    virtual size_t step(size_t max_bytes, AddressInfo &info, unsigned flags,
                        bool tentative = false) = 0;
    virtual size_t step_custom(size_t max_bytes, AddressInfoCustom &info,
                               bool tentative = false) = 0;
 
    virtual void confirm_step(void) = 0;
    virtual void cancel_step(void) = 0;
 
    virtual bool get_addresses(AddressList &addrlist,
                               const InstanceLayoutPieceBase *&nonaffine) = 0;
  };
 
  //
  // class TransferIteratorBase<N,T>
  //
 
  template <int N, typename T>
  class TransferIteratorBase : public TransferIterator {
  protected:
    TransferIteratorBase(void); // used by deserializer
  public:
    TransferIteratorBase(RegionInstanceImpl *_inst_impl, const int _dim_order[N]);
 
    virtual Event request_metadata(void);
 
    virtual void reset(void);
    virtual bool done(void);
    virtual size_t step(size_t max_bytes, AddressInfo &info, unsigned flags,
                        bool tentative = false);
    virtual size_t step_custom(size_t max_bytes, AddressInfoCustom &info,
                               bool tentative = false);
 
    virtual void confirm_step(void);
    virtual void cancel_step(void);
 
    virtual size_t get_base_offset(void) const;
 
    virtual bool get_addresses(AddressList &addrlist,
                               const InstanceLayoutPieceBase *&nonaffine);
 
  protected:
    virtual bool get_next_rect(Rect<N, T> &r, FieldID &fid, size_t &offset,
                               size_t &fsize) = 0;
 
    bool have_rect, is_done;
    Rect<N, T> cur_rect;
    FieldID cur_field_id;
    size_t cur_field_offset, cur_field_size;
    Point<N, T> cur_point, next_point;
    bool carry;
 
    RegionInstanceImpl *inst_impl;
    // InstanceLayout<N, T> *inst_layout;
    size_t inst_offset;
    bool tentative_valid;
    int dim_order[N];
  };
 
  //
  // class TransferIteratorIndexSpace<N,T>
  //
 
  template <int N, typename T>
  class TransferIteratorIndexSpace : public TransferIteratorBase<N, T> {
  protected:
    TransferIteratorIndexSpace(void); // used by deserializer
  public:
    TransferIteratorIndexSpace(const int _dim_order[N],
                               const std::vector<FieldID> &_fields,
                               const std::vector<size_t> &_fld_offsets,
                               const std::vector<size_t> &_fld_sizes,
                               RegionInstanceImpl *_inst_impl,
                               const IndexSpace<N, T> &_is);
 
    TransferIteratorIndexSpace(const int _dim_order[N],
                               const std::vector<FieldID> &_fields,
                               const std::vector<size_t> &_fld_offsets,
                               const std::vector<size_t> &_fld_sizes,
                               RegionInstanceImpl *_inst_impl, const Rect<N, T> &_bounds,
                               SparsityMapImpl<N, T> *_sparsity_impl);
 
    template <typename S>
    static TransferIterator *deserialize_new(S &deserializer);
 
    virtual ~TransferIteratorIndexSpace(void);
 
    virtual Event request_metadata(void);
 
    virtual void reset(void);
 
    static Serialization::PolymorphicSerdezSubclass<TransferIterator,
                                                    TransferIteratorIndexSpace<N, T>>
        serdez_subclass;
 
    template <typename S>
    bool serialize(S &serializer) const;
 
  protected:
    void reset_internal(void);
    virtual bool get_next_rect(Rect<N, T> &r, FieldID &fid, size_t &offset,
                               size_t &fsize);
 
    IndexSpace<N, T> is;
    SparsityMapImpl<N, T> *sparsity_impl{nullptr};
    IndexSpaceIterator<N, T> iter;
    bool iter_init_deferred{false};
    std::vector<FieldID> fields;
    std::vector<size_t> fld_offsets, fld_sizes;
    size_t field_idx{0};
  };
 
  //
  // class IDIndexedFieldsIterator<N,T>
  //
 
  template <int N, typename T>
  class IDIndexedFieldsIterator : public TransferIteratorBase<N, T> {
  protected:
    IDIndexedFieldsIterator(void);
 
  public:
    IDIndexedFieldsIterator(const int _dim_order[N], const std::vector<FieldID> &_fields,
                            size_t _field_size, RegionInstanceImpl *_inst_impl,
                            const IndexSpace<N, T> &_is, ReplicatedHeap *_repl_heap);
 
    template <typename S>
    static TransferIterator *deserialize_new(S &deserializer);
 
    virtual ~IDIndexedFieldsIterator(void);
 
    Event request_metadata(void) override;
    void reset(void) override;
 
    static Serialization::PolymorphicSerdezSubclass<TransferIterator,
                                                    IDIndexedFieldsIterator<N, T>>
        serdez_subclass;
 
    template <typename S>
    bool serialize(S &serializer) const;
 
    bool get_addresses(AddressList &addrlist,
                       const InstanceLayoutPieceBase *&nonaffine) override;
 
    size_t step(size_t max_bytes, TransferIterator::AddressInfo &info, unsigned flags,
                bool tentative = false) override;
    size_t step_custom(size_t max_bytes, TransferIterator::AddressInfoCustom &info,
                       bool tentative = false) override;
    void confirm_step(void) override;
    void cancel_step(void) override;
 
  protected:
    void reset_internal(void);
 
    bool get_next_rect(Rect<N, T> &r, FieldID &fid, size_t &offset,
                       size_t &fsize) override;
 
    IndexSpace<N, T> is;
    SparsityMapImpl<N, T> *sparsity_impl{nullptr};
    IndexSpaceIterator<N, T> iter;
    bool iter_init_deferred{false};
    std::vector<FieldID> fields;
 
    // const InstanceLayoutPiece<N, T> *layout_piece{nullptr};
    const InstanceLayout<N, T> *inst_layout{nullptr};
 
    size_t field_size{0};
    size_t rect_idx{0};
 
    ReplicatedHeap *repl_heap{nullptr};
    FieldBlock *field_block{nullptr};
  };
 
  template <int N, typename T>
  class TransferIteratorIndirect : public TransferIteratorBase<N, T> {
  protected:
    TransferIteratorIndirect(void); // used by deserializer
  public:
    TransferIteratorIndirect(Memory _addrs_mem, RegionInstanceImpl *_inst_impl,
                             const std::vector<FieldID> &_fields,
                             const std::vector<size_t> &_fld_offsets,
                             const std::vector<size_t> &_fld_sizes);
 
    template <typename S>
    static TransferIterator *deserialize_new(S &deserializer);
 
    virtual ~TransferIteratorIndirect(void);
 
    virtual Event request_metadata(void);
 
    // specify the xd port used for indirect address flow control, if any
    virtual void set_indirect_input_port(XferDes *xd, int port_idx,
                                         TransferIterator *inner_iter);
    virtual void reset(void);
 
    static Serialization::PolymorphicSerdezSubclass<TransferIterator,
                                                    TransferIteratorIndirect<N, T>>
        serdez_subclass;
 
    template <typename S>
    bool serialize(S &serializer) const;
 
  protected:
    virtual bool get_next_rect(Rect<N, T> &r, FieldID &fid, size_t &offset,
                               size_t &fsize);
 
    TransferIterator *addrs_in{nullptr};
    Memory addrs_mem{Memory::NO_MEMORY};
    intptr_t addrs_mem_base{0};
    bool can_merge{true};
    static constexpr size_t MAX_POINTS = 64;
    Point<N, T> points[MAX_POINTS];
    size_t point_pos{0}, num_points{0};
    std::vector<FieldID> fields;
    std::vector<size_t> fld_offsets, fld_sizes;
    XferDes *indirect_xd{nullptr};
    int indirect_port_idx{-1};
  };
 
  class TransferDomain {
  protected:
    TransferDomain(void);
 
  public:
    template <typename S>
    static TransferDomain *deserialize_new(S &deserializer);
 
    template <int N, typename T>
    static TransferDomain *construct(const IndexSpace<N, T> &is);
 
    virtual TransferDomain *clone(void) const = 0;
 
    virtual ~TransferDomain(void);
 
    virtual Event request_metadata(void) = 0;
 
    virtual bool empty(void) const = 0;
    virtual size_t volume(void) const = 0;
 
    virtual void choose_dim_order(std::vector<int> &dim_order,
                                  const std::vector<CopySrcDstField> &srcs,
                                  const std::vector<CopySrcDstField> &dsts,
                                  const std::vector<IndirectionInfo *> &indirects,
                                  bool force_fortran_order, size_t max_stride) const = 0;
 
    virtual void count_fragments(RegionInstance inst, const std::vector<int> &dim_order,
                                 const std::vector<FieldID> &fields,
                                 const std::vector<size_t> &fld_sizes,
                                 std::vector<size_t> &fragments) const = 0;
 
    virtual TransferIterator *create_iterator(RegionInstance inst,
                                              const std::vector<int> &dim_order,
                                              const std::vector<FieldID> &fields,
                                              const std::vector<size_t> &fld_offsets,
                                              const std::vector<size_t> &fld_sizes,
                                              bool idindexed_fields = false) const = 0;
 
    virtual TransferIterator *
    create_iterator(RegionInstance inst, RegionInstance peer,
                    const std::vector<FieldID> &fields,
                    const std::vector<size_t> &fld_offsets,
                    const std::vector<size_t> &fld_sizes) const = 0;
 
    virtual void print(std::ostream &os) const = 0;
  };
 
  class TransferOperation;
 
  // copies with generalized scatter and gather have a DAG that describes
  //  the overall transfer: nodes are transfer descriptors and edges are
  //  intermediate buffers
  struct TransferGraph {
    struct XDTemplate {
      // TODO(apryakhin@): Remove target_node
      NodeID target_node;
      // XferDesKind kind;
      XferDesFactory *factory;
      int gather_control_input;
      int scatter_control_input;
      XferDesRedopInfo redop;
      Channel *channel = nullptr;
      bool idindexed_fields = false;
 
      enum IOType
      {
        IO_INST,
        IO_INDIRECT_INST,
        IO_EDGE,
        IO_FILL_DATA
      };
      struct IO {
        IOType iotype;
        union {
          struct {
            RegionInstance inst;
            unsigned fld_start;
            unsigned fld_count;
          } inst;
          struct {
            unsigned ind_idx;
            unsigned port;
            RegionInstance inst;
            unsigned fld_start;
            unsigned fld_count;
          } indirect;
          unsigned edge;
          struct {
            unsigned fill_start;
            unsigned fill_size;
            size_t fill_total;
          } fill;
        };
      };
      static IO mk_inst(RegionInstance _inst, unsigned _fld_start, unsigned _fld_count);
      static IO mk_indirect(unsigned _ind_idx, unsigned _port, RegionInstance _inst,
                            unsigned _fld_start, unsigned _fld_count);
      static IO mk_edge(unsigned _edge);
      static IO mk_fill(unsigned _fill_start, unsigned _fill_size, size_t _fill_total);
 
      std::vector<IO> inputs; // TODO: short vectors
      std::vector<IO> outputs;
 
      // helper functions for initializing these things
      void set_simple(Channel *channel, int in_edge, int out_edge);
    };
    struct IBInfo {
      Memory memory;
      size_t size;
    };
    std::vector<XDTemplate> xd_nodes;
    std::vector<IBInfo> ib_edges;
    std::vector<unsigned> ib_alloc_order;
  };
 
  class TransferDesc {
  public:
    // Copy the srcs, dsts, and indirects
    template <int N, typename T>
    TransferDesc(
        IndexSpace<N, T> _is, const std::vector<CopySrcDstField> &_srcs,
        const std::vector<CopySrcDstField> &_dsts,
        const std::vector<const typename CopyIndirection<N, T>::Base *> &_indirects,
        const ProfilingRequestSet &requests);
 
    // Move the srcs, dsts, and indirects
    template <int N, typename T>
    TransferDesc(
        IndexSpace<N, T> _is, std::vector<CopySrcDstField> &&_srcs,
        std::vector<CopySrcDstField> &&_dsts,
        const std::vector<const typename CopyIndirection<N, T>::Base *> &_indirects,
        const ProfilingRequestSet &requests);
 
  private:
    template <int N, typename T, typename SrcVec, typename DstVec>
    TransferDesc(
        IndexSpace<N, T> _is, SrcVec &&_srcs, DstVec &&_dsts,
        const std::vector<const typename CopyIndirection<N, T>::Base *> &_indirects,
        const ProfilingRequestSet &requests,
        std::true_type); // the true_type is used to disambiguate the constructor
 
  protected:
    // reference-counted - do not delete directly
    ~TransferDesc();
 
  public:
    void add_reference();
    void remove_reference();
 
    struct FieldInfo {
      FieldID id;
      size_t offset, size;
      CustomSerdezID serdez_id;
    };
 
  protected:
    atomic<int> refcount;
 
    void check_analysis_preconditions(std::vector<Event> &preconditions) const;
    [[nodiscard]] bool perform_analysis(TransferOperation *op, TimeLimit work_until);
 
    friend class TransferOperation;
 
    TransferDomain *domain;
    std::vector<CopySrcDstField> srcs, dsts;
    std::vector<IndirectionInfo *> indirects;
    ProfilingRequestSet prs;
 
    Mutex mutex;
    TransferGraph graph;
    std::vector<int> dim_order;
    std::vector<FieldInfo> src_fields, dst_fields;
    void *fill_data;
    size_t fill_size;
    bool analysis_init_done = false;
    size_t analysis_field_idx = 0;
    size_t analysis_fld_start = 0;
    size_t analysis_fill_ofs = 0;
    std::vector<bool> analysis_field_done;
    ProfilingMeasurements::OperationMemoryUsage prof_usage;
    ProfilingMeasurements::OperationCopyInfo prof_cpinfo;
  };
 
  class CopyAnalyzer : public BackgroundWorkItem {
  public:
    CopyAnalyzer(void);
 
    void analyze_copy(TransferOperation *op);
 
    // push an op that has already begun processing back on the front of the
    //  queue, e.g. when the tail of the async IB response path hits a timeout
    void requeue_front(TransferOperation *op);
 
    virtual bool do_work(TimeLimit work_until) override;
 
  protected:
    Mutex mutex;
    std::deque<TransferOperation *> pending_copies;
  };
 
  class IndirectionInfo {
  public:
    virtual ~IndirectionInfo(void) {}
    virtual Event request_metadata(void) = 0;
 
    virtual void
    generate_gather_paths(const Node *node_info, Memory dst_mem,
                          TransferGraph::XDTemplate::IO dst_edge, unsigned indirect_idx,
                          unsigned src_fld_start, unsigned src_fld_count,
                          size_t bytes_per_element, CustomSerdezID serdez_id,
                          std::vector<TransferGraph::XDTemplate> &xd_nodes,
                          std::vector<TransferGraph::IBInfo> &ib_edges,
                          std::vector<TransferDesc::FieldInfo> &src_fields) = 0;
 
    virtual void generate_scatter_paths(
        Memory src_mem, TransferGraph::XDTemplate::IO src_edge, unsigned indirect_idx,
        unsigned dst_fld_start, unsigned dst_fld_count, size_t bytes_per_element,
        CustomSerdezID serdez_id, std::vector<TransferGraph::XDTemplate> &xd_nodes,
        std::vector<TransferGraph::IBInfo> &ib_edges,
        std::vector<TransferDesc::FieldInfo> &src_fields) = 0;
 
    virtual RegionInstance get_pointer_instance(void) const = 0;
 
    virtual const std::vector<RegionInstance> *get_instances(void) const = 0;
 
    virtual FieldID get_field(void) const = 0;
 
    virtual TransferIterator *create_address_iterator(RegionInstance peer) const = 0;
 
    virtual TransferIterator *create_indirect_iterator(
        Memory addrs_mem, RegionInstance inst, const std::vector<FieldID> &fields,
        const std::vector<size_t> &fld_offsets, const std::vector<size_t> &fld_sizes,
        Channel *channel = nullptr) const = 0;
 
    virtual void print(std::ostream &os) const = 0;
  };
 
  std::ostream &operator<<(std::ostream &os, const IndirectionInfo &ii);
 
  class IndirectionInfoBase : public IndirectionInfo {
  public:
    IndirectionInfoBase(bool _structured, FieldID _field_id, RegionInstance _inst,
                        bool _is_ranges, bool _oor_possible, bool _aliasing_possible,
                        size_t _subfield_offset, const std::vector<RegionInstance> _insts,
                        Channel *_addrsplit_channel);
 
  protected:
    // most of the logic to generate unstructured gather/scatter paths is
    // dimension-agnostic and we can define it in a base class to save
    // compile time/code size ...
    virtual void generate_gather_paths(const Node *nodes_info, Memory dst_mem,
                                       TransferGraph::XDTemplate::IO dst_edge,
                                       unsigned indirect_idx, unsigned src_fld_start,
                                       unsigned src_fld_count, size_t bytes_per_element,
                                       CustomSerdezID serdez_id,
                                       std::vector<TransferGraph::XDTemplate> &xd_nodes,
                                       std::vector<TransferGraph::IBInfo> &ib_edges,
                                       std::vector<TransferDesc::FieldInfo> &src_fields);
 
    virtual void generate_scatter_paths(Memory src_mem,
                                        TransferGraph::XDTemplate::IO src_edge,
                                        unsigned indirect_idx, unsigned dst_fld_start,
                                        unsigned dst_fld_count, size_t bytes_per_element,
                                        CustomSerdezID serdez_id,
                                        std::vector<TransferGraph::XDTemplate> &xd_nodes,
                                        std::vector<TransferGraph::IBInfo> &ib_edges,
                                        std::vector<TransferDesc::FieldInfo> &src_fields);
 
    // ... but we need three helpers that will be defined in the typed versions
    virtual size_t num_spaces() const = 0;
    virtual void populate_copy_info(ChannelCopyInfo &info) const = 0;
    virtual size_t domain_size() const = 0;
    virtual size_t address_size() const = 0;
 
    virtual XferDesFactory *create_addrsplit_factory(size_t bytes_per_element) const = 0;
 
    bool structured;
    FieldID field_id;
    RegionInstance inst;
    bool is_ranges;
    bool oor_possible;
    bool aliasing_possible;
    size_t subfield_offset;
    std::vector<RegionInstance> insts;
    Channel *addrsplit_channel;
  };
 
  //
  // class IndirectionInfoTyped<N,T,N2,T2>
  //
 
  template <int N, typename T, int N2, typename T2>
  class IndirectionInfoTyped : public IndirectionInfoBase {
  public:
    IndirectionInfoTyped(
        const IndexSpace<N, T> &is,
        const typename CopyIndirection<N, T>::template Unstructured<N2, T2> &ind,
        Channel *_addr_split_channel);
 
    virtual Event request_metadata(void);
 
    virtual RegionInstance get_pointer_instance(void) const;
 
    virtual const std::vector<RegionInstance> *get_instances(void) const;
 
    virtual FieldID get_field(void) const;
 
    virtual TransferIterator *create_address_iterator(RegionInstance peer) const;
 
    virtual TransferIterator *create_indirect_iterator(
        Memory addrs_mem, RegionInstance inst, const std::vector<FieldID> &fields,
        const std::vector<size_t> &fld_offsets, const std::vector<size_t> &fld_sizes,
        Channel *channel = nullptr) const;
 
    virtual void print(std::ostream &os) const;
 
  protected:
    virtual size_t num_spaces() const;
    virtual void populate_copy_info(ChannelCopyInfo &info) const;
    virtual size_t domain_size() const;
    virtual size_t address_size() const;
 
    virtual XferDesFactory *create_addrsplit_factory(size_t bytes_per_element) const;
 
    IndexSpace<N, T> domain;
    std::vector<IndexSpace<N2, T2>> spaces;
    Channel *addr_split_channel;
  };
 
  // a TransferOperation is an application-requested copy/fill/reduce
  class TransferOperation : public Operation {
  public:
    TransferOperation(TransferDesc &_desc, Event _precondition,
                      GenEventImpl *_finish_event, EventImpl::gen_t _finish_gen,
                      int priority);
 
    ~TransferOperation();
 
    inline int get_priority(void) const { return priority; }
    inline bool analyze(TimeLimit work_until)
    {
      return desc.perform_analysis(this, work_until);
    }
 
    virtual void print(std::ostream &os) const;
 
    void start_or_defer(void);
 
    virtual bool mark_ready(void);
    virtual bool mark_started(void);
 
    bool allocate_ibs(TimeLimit work_until);
    bool create_xds(TimeLimit work_until);
 
    void notify_ib_allocation(unsigned ib_index, off_t ib_offset, TimeLimit work_until);
    void notify_ib_allocations(unsigned count, unsigned first_index, const off_t *offsets,
                               TimeLimit work_until);
    void notify_xd_completion(XferDesID xd_id);
 
    class XDLifetimeTracker : public Operation::AsyncWorkItem {
    public:
      XDLifetimeTracker(TransferOperation *_op, XferDesID _xd_id);
      virtual void request_cancellation(void);
      virtual void print(std::ostream &os) const;
 
    protected:
      XferDesID xd_id;
    };
 
  protected:
    virtual void mark_completed(void);
 
    class DeferredStart : public EventWaiter {
    public:
      DeferredStart(TransferOperation *_op);
      virtual void event_triggered(bool poisoned, TimeLimit work_until);
      virtual void print(std::ostream &os) const;
      virtual Event get_finish_event(void) const;
 
      TransferOperation *op;
      Event precondition;
    };
    DeferredStart deferred_start;
 
    TransferDesc &desc;
    Event precondition;
    std::vector<XferDesID> xd_ids;
    std::vector<XDLifetimeTracker *> xd_trackers;
    std::vector<off_t> ib_offsets;
    atomic<unsigned> ib_responses_needed;
    int priority;
 
    // resume state for incremental allocate_ibs / create_xds across timeouts
    bool allocate_ibs_init_done{false};
    bool allocate_ibs_requests_sent{false};
    unsigned allocate_ibs_immed_count{0};
    bool create_xds_init_done{false};
    size_t create_xds_i{0};
    std::vector<std::pair<XferDesID, int>> ib_pre_ids;
    std::vector<std::pair<XferDesID, int>> ib_next_ids;
  };
 
  template <int N, typename T>
  using CopyImplFn =
      Event (*)(const IndexSpace<N, T> &, const std::vector<CopySrcDstField> &,
                const std::vector<CopySrcDstField> &,
                const std::vector<const typename CopyIndirection<N, T>::Base *> &,
                const Realm::ProfilingRequestSet &, Event, int);
 
  template <int N, typename T>
  struct CopyImplRouter {
    static CopyImplFn<N, T> impl;
  };
 
}; // namespace Realm
 
#include "realm/transfer/transfer.inl"
 
#endif // ifndef REALM_TRANSFER_H