device/interface/mark_dcontext.cxx

#include "petscdevice_interface_internal.hpp" /*I <petscdevice.h> I*/

#include <petsc/private/cpp/object_pool.hpp>
#include <petsc/private/cpp/utility.hpp>

#include <unordered_map>
#include <algorithm> // std::remove_if(), std::find_if()
#include <vector>
#include <string>
#include <sstream> // std::ostringstream

// ==========================================================================================
// PetscEvent
// ==========================================================================================

struct PetscEventAllocator : public Petsc::AllocatorBase<PetscEvent> {
  PETSC_NODISCARD static PetscErrorCode create(PetscEvent *event) noexcept {
    PetscFunctionBegin;
    PetscCall(PetscNew(event));
    PetscFunctionReturn(0);
  }

  PETSC_NODISCARD static PetscErrorCode destroy(PetscEvent event) noexcept {
    PetscFunctionBegin;
    PetscCall(reset(event));
    PetscCall(PetscFree(event));
    PetscFunctionReturn(0);
  }

  PETSC_NODISCARD static PetscErrorCode reset(PetscEvent event, bool zero = true) noexcept {
    PetscFunctionBegin;
    if (zero) {
      if (auto &destroy = event->destroy) {
        PetscCall((*destroy)(event));
        destroy = nullptr;
      }
      event->dctx_id    = 0;
      event->dctx_state = 0;
      PetscAssert(!event->data, PETSC_COMM_SELF, PETSC_ERR_PLIB, "Event failed to destroy its data member: %p", event->data);
    }
    event->dtype = PETSC_DEVICE_DEFAULT();
    PetscFunctionReturn(0);
  }
};

static Petsc::ObjectPool<PetscEvent, PetscEventAllocator> event_pool;

static PetscErrorCode PetscDeviceContextCreateEvent_Private(PetscDeviceContext dctx, PetscEvent *event) {
  PetscFunctionBegin;
  PetscValidDeviceContext(dctx, 1);
  PetscValidPointer(event, 2);
  PetscCall(event_pool.allocate(event));
  PetscCall(PetscDeviceContextGetDeviceType(dctx, &(*event)->dtype));
  PetscTryTypeMethod(dctx, createevent, *event);
  PetscFunctionReturn(0);
}

static PetscErrorCode PetscEventDestroy_Private(PetscEvent *event) {
  PetscFunctionBegin;
  PetscValidPointer(event, 1);
  if (*event) PetscCall(event_pool.deallocate(Petsc::util::exchange(*event, nullptr)));
  PetscFunctionReturn(0);
}

static PetscErrorCode PetscDeviceContextRecordEvent_Private(PetscDeviceContext dctx, PetscEvent event) {
  PetscObjectId    id;
  PetscObjectState state;

  PetscFunctionBegin;
  PetscValidDeviceContext(dctx, 1);
  PetscValidPointer(event, 2);
  id    = PetscObjectCast(dctx)->id;
  state = PetscObjectCast(dctx)->state;
  // technically state can never be less than event->dctx_state (only equal) but we include
  // it in the check just in case
  if ((id == event->dctx_id) && (state <= event->dctx_state)) PetscFunctionReturn(0);
  if (dctx->ops->recordevent) {
    // REVIEW ME:
    // TODO maybe move this to impls, as they can determine whether they can interoperate with
    // other device types more readily
    if (PetscDefined(USE_DEBUG) && (event->dtype != PETSC_DEVICE_HOST)) {
      PetscDeviceType dtype;

      PetscCall(PetscDeviceContextGetDeviceType(dctx, &dtype));
      PetscCheck(event->dtype == dtype, PETSC_COMM_SELF, PETSC_ERR_ARG_INCOMP, "Event type %s does not match device context type %s", PetscDeviceTypes[event->dtype], PetscDeviceTypes[dtype]);
    }
    PetscUseTypeMethod(dctx, recordevent, event);
  }
  event->dctx_id    = id;
  event->dctx_state = state;
  PetscFunctionReturn(0);
}

static PetscErrorCode PetscDeviceContextWaitForEvent_Private(PetscDeviceContext dctx, PetscEvent event) {
  PetscFunctionBegin;
  PetscValidDeviceContext(dctx, 1);
  PetscValidPointer(event, 2);
  // empty data implies you cannot wait on this event
  if (!event->data) PetscFunctionReturn(0);
  if (PetscDefined(USE_DEBUG)) {
    const auto      etype = event->dtype;
    PetscDeviceType dtype;

    PetscCall(PetscDeviceContextGetDeviceType(dctx, &dtype));
    PetscCheck(etype == dtype, PETSC_COMM_SELF, PETSC_ERR_ARG_INCOMP, "Event type %s does not match device context type %s", PetscDeviceTypes[etype], PetscDeviceTypes[dtype]);
  }
  if (PetscObjectCast(dctx)->id == event->dctx_id) PetscFunctionReturn(0);
  PetscTryTypeMethod(dctx, waitforevent, event);
  PetscFunctionReturn(0);
}

// ==========================================================================================
// PetscStackFrame
//
// A helper class that (when debugging is enabled) contains the stack frame from which
// PetscDeviceContextMakrIntentFromID(). It is intended to be derived from, since this enables
// empty-base-class optimization to kick in when debugging is disabled.
// ==========================================================================================

template <bool use_debug>
struct PetscStackFrame;

template <>
struct PetscStackFrame</* use_debug = */ true> {
  std::string file{};
  std::string function{};
  int         line{};

  PetscStackFrame() = default;

  PetscStackFrame(const char *file_, const char *func_, int line_) noexcept : file(split_on_petsc_path_(file_)), function(func_), line(line_) { }

  bool operator==(const PetscStackFrame &other) const noexcept { return line == other.line && file == other.file && function == other.function; }

private:
  static std::string split_on_petsc_path_(std::string &&in) noexcept {
    auto pos = in.find("petsc/src");

    if (pos == std::string::npos) pos = in.find("petsc/include");
    if (pos == std::string::npos) pos = 0;
    return in.substr(pos);
  }

  friend std::ostream &operator<<(std::ostream &os, const PetscStackFrame &frame) {
    os << '(' << frame.function << "() at " << frame.file << ':' << frame.line << ')';
    return os;
  }
};

template <>
struct PetscStackFrame</* use_debug = */ false> {
  template <typename... T>
  constexpr PetscStackFrame(T &&...) noexcept { }

  constexpr bool operator==(const PetscStackFrame &) const noexcept { return true; }

  friend std::ostream &operator<<(std::ostream &os, const PetscStackFrame &) noexcept {
    os << "(unknown)";
    return os;
  }
};

// ==========================================================================================
// MarkedObjectMap
//
// A mapping from a PetscObjectId to a PetscEvent and (if debugging is enabled) a
// PetscStackFrame containing the location where PetscDeviceContextMarkIntentFromID was called
// ==========================================================================================

class MarkedObjectMap : public Petsc::RegisterFinalizeable<MarkedObjectMap> {
public:
  // Note we derive from PetscStackFrame so that the empty base class optimization can kick
  // in. If it were just a member it would still take up storage in optimized builds
  class snapshot_type : private PetscStackFrame<PetscDefined(USE_DEBUG)> {
  public:
    using frame_type = PetscStackFrame<PetscDefined(USE_DEBUG)>;

    snapshot_type() = default;
    snapshot_type(PetscDeviceContext, frame_type) noexcept;

    ~snapshot_type() noexcept;

    // movable
    snapshot_type(snapshot_type &&) noexcept;
    snapshot_type &operator=(snapshot_type &&) noexcept;

    // not copyable
    snapshot_type(const snapshot_type &) noexcept            = delete;
    snapshot_type &operator=(const snapshot_type &) noexcept = delete;

    PETSC_NODISCARD PetscEvent        event() const noexcept { return event_; }
    PETSC_NODISCARD const frame_type &frame() const noexcept { return *this; }
    PETSC_NODISCARD frame_type       &frame() noexcept { return *this; }
    PETSC_NODISCARD PetscObjectId     dctx_id() const noexcept { return event()->dctx_id; }

  private:
    PetscEvent event_{}; // the state of device context when this snapshot was recorded

    PETSC_NODISCARD static PetscEvent init_event_(PetscDeviceContext) noexcept;
  };

  // the "value" each key maps to
  struct mapped_type {
    using dependency_type = std::vector<snapshot_type>;

    PetscMemoryAccessMode mode = PETSC_MEMORY_ACCESS_READ;
    snapshot_type         last_write{};
    dependency_type       dependencies{};
  };

  using map_type = std::unordered_map<PetscObjectId, mapped_type>;

  map_type map;

private:
  friend class RegisterFinalizeable<MarkedObjectMap>;

  PETSC_NODISCARD PetscErrorCode finalize_() noexcept;
};

// ==========================================================================================
// MarkedObejctMap Private API
// ==========================================================================================

inline PetscErrorCode MarkedObjectMap::finalize_() noexcept {
  PetscFunctionBegin;
  PetscCall(PetscInfo(nullptr, "Finalizing marked object map\n"));
  if (PetscDefined(USE_DEBUG)) {
    std::ostringstream oss;
    auto               wrote_to_oss = false;
    const auto         end          = this->map.cend();
    PetscMPIInt        rank;

    PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
    for (auto it = this->map.cbegin(); it != end; ++it) {
      // need a temporary since we want to prepend "object xxx has orphaned dependencies" if
      // any of the dependencies have orphans. but we also need to check that in the loop, so
      // use a temporary to accumulate and then build the rest from it.
      std::ostringstream oss_tmp;
      auto               wrote_to_oss_tmp = false;
      //const auto        &mapped           = it->second;
      //const auto         mode             = PetscMemoryAccessModes(mapped.mode);

      // for (auto &&dep : mapped.dependencies) {
      //   // if (!dep.ctx->options.allow_orphans) {
      //   //   wrote_to_oss_tmp = true;
      //   //   oss_tmp<<"  ["<<rank<<"] dctx "<<dep.ctx<<" (id "<<dep.dctx_id()<<", state "<<dep.dctx_state<<", intent "<<mode<<' '<<dep.frame()<<")\n";
      //   // }
      // }
      // check if we wrote to it
      if (wrote_to_oss_tmp) {
        oss << '[' << rank << "] object " << it->first << " has orphaned dependencies:\n" << oss_tmp.str();
        wrote_to_oss = true;
      }
    }
    if (wrote_to_oss) {
      //PetscCall((*PetscErrorPrintf)("%s\n",oss.str().c_str()));
      //SETERRQ(PETSC_COMM_SELF,PETSC_ERR_PLIB,"Orphaned dependencies found, see above");
    }
  }
  // replace with new map, since clear() does not necessarily free memory
  PetscCallCXX(this->map = map_type{});
  PetscFunctionReturn(0);
}

// ==========================================================================================
// MarkedObejctMap::snapshot_type Private API
// ==========================================================================================

inline PetscEvent MarkedObjectMap::snapshot_type::init_event_(PetscDeviceContext dctx) noexcept {
  PetscEvent event = nullptr;

  PetscFunctionBegin;
  PetscCallAbort(PETSC_COMM_SELF, PetscDeviceContextCreateEvent_Private(dctx, &event));
  PetscCallAbort(PETSC_COMM_SELF, PetscDeviceContextRecordEvent_Private(dctx, event));
  PetscFunctionReturn(event);
}

// ==========================================================================================
// MarkedObejctMap::snapshot_type Public API
// ==========================================================================================

MarkedObjectMap::snapshot_type::snapshot_type(PetscDeviceContext dctx, frame_type frame) noexcept : frame_type(std::move(frame)), event_(init_event_(dctx)) { }

MarkedObjectMap::snapshot_type::~snapshot_type() noexcept {
  PetscFunctionBegin;
  PetscCallAbort(PETSC_COMM_SELF, PetscEventDestroy_Private(&event_));
  PetscFunctionReturnVoid();
}

// movable
MarkedObjectMap::snapshot_type::snapshot_type(snapshot_type &&other) noexcept : frame_type(std::move(other)), event_(Petsc::util::exchange(other.event_, nullptr)) { }

MarkedObjectMap::snapshot_type &MarkedObjectMap::snapshot_type::operator=(snapshot_type &&other) noexcept {
  PetscFunctionBegin;
  if (this != &other) {
    frame_type::operator=(std::move(other));
    PetscCallAbort(PETSC_COMM_SELF, PetscEventDestroy_Private(&event_));
    event_ = Petsc::util::exchange(other.event_, nullptr);
  }
  PetscFunctionReturn(*this);
}

// A mapping between PetscObjectId (i.e. some PetscObject) to the list of PetscEvent's encoding
// the last time the PetscObject was accessed
static MarkedObjectMap marked_object_map;

// ==========================================================================================
// Utility Functions
// ==========================================================================================

template <typename T>
static PetscErrorCode PetscDeviceContextMapIterVisitor(PetscDeviceContext dctx, T &&callback) noexcept {
  const auto dctx_id    = PetscObjectCast(dctx)->id;
  auto      &dctx_deps  = CxxDataCast(dctx)->deps;
  auto      &object_map = marked_object_map.map;

  PetscFunctionBegin;
  for (auto &&dep : dctx_deps) {
    const auto mapit = object_map.find(dep);

    // Need this check since the final PetscDeviceContext may run through this *after* the map
    // has been finalized (and cleared), and hence might fail to find its dependencies. This is
    // perfectly valid since the user no longer cares about dangling dependencies after PETSc
    // is finalized
    if (PetscLikely(mapit != object_map.end())) {
      auto      &deps = mapit->second.dependencies;
      const auto end  = deps.end();
      const auto it   = std::remove_if(deps.begin(), end, [&](const MarkedObjectMap::snapshot_type &obj) { return obj.dctx_id() == dctx_id; });

      PetscCall(callback(mapit, deps.cbegin(), static_cast<decltype(deps.cend())>(it)));
      // remove ourselves
      PetscCallCXX(deps.erase(it, end));
      // continue to next object, but erase this one if it has no more dependencies
      if (deps.empty()) PetscCallCXX(object_map.erase(mapit));
    }
  }
  PetscCallCXX(dctx_deps.clear());
  PetscFunctionReturn(0);
}

PetscErrorCode PetscDeviceContextSyncClearMap_Internal(PetscDeviceContext dctx) {
  using map_iterator = MarkedObjectMap::map_type::const_iterator;
  using dep_iterator = MarkedObjectMap::mapped_type::dependency_type::const_iterator;

  PetscFunctionBegin;
  PetscCall(PetscDeviceContextMapIterVisitor(dctx, [&](map_iterator mapit, dep_iterator it, dep_iterator end) {
    PetscFunctionBegin;
    if (PetscDefined(USE_DEBUG_AND_INFO)) {
      std::ostringstream oss;
      const auto         mode = PetscMemoryAccessModeToString(mapit->second.mode);

      oss << "synced dctx " << PetscObjectCast(dctx)->id << ", remaining leaves for obj " << mapit->first << ": {";
      while (it != end) {
        oss << "[dctx " << it->dctx_id() << ", " << mode << ' ' << it->frame() << ']';
        if (++it != end) oss << ", ";
      }
      oss << '}';
      PetscCall(PetscInfo(nullptr, "%s\n", oss.str().c_str()));
    }
    PetscFunctionReturn(0);
  }));
  {
    // the recursive sync clear map call is unbounded in case of a dependenct loop so we make a
    // copy
    // clang-format off
    const std::vector<CxxData::upstream_type::value_type> upstream_copy(
      std::make_move_iterator(CxxDataCast(dctx)->upstream.begin()),
      std::make_move_iterator(CxxDataCast(dctx)->upstream.end())
    );
    // clang-format on

    // aftermath, clear our set of parents (to avoid infinite recursion) and mark ourselves as no
    // longer contained (while the empty graph technically *is* always contained, it is not what
    // we mean by it)
    PetscCall(CxxDataCast(dctx)->clear());
    //dctx->contained = PETSC_FALSE;
    for (auto &&upstrm : upstream_copy) {
      // check that this parent still points to what we originally thought it was
      PetscCheck(upstrm.second.id == PetscObjectCast(upstrm.first)->id, PETSC_COMM_SELF, PETSC_ERR_PLIB, "Upstream dctx %" PetscInt64_FMT " no longer exists, now has id %" PetscInt64_FMT, upstrm.second.id, PetscObjectCast(upstrm.first)->id);
      PetscCall(PetscDeviceContextSyncClearMap_Internal(upstrm.first));
    }
  }
  PetscFunctionReturn(0);
}

PetscErrorCode PetscDeviceContextCheckNotOrphaned_Internal(PetscDeviceContext dctx) {
  std::ostringstream oss;
  //const auto         allow = dctx->options.allow_orphans, contained = dctx->contained;
  const auto         allow = true, contained = true;
  auto               wrote_to_oss = false;
  using map_iterator              = MarkedObjectMap::map_type::const_iterator;
  using dep_iterator              = MarkedObjectMap::mapped_type::dependency_type::const_iterator;

  PetscFunctionBegin;
  PetscCall(PetscDeviceContextMapIterVisitor(dctx, [&](map_iterator mapit, dep_iterator it, dep_iterator end) {
    PetscFunctionBegin;
    if (allow || contained) PetscFunctionReturn(0);
    wrote_to_oss = true;
    oss << "- PetscObject (id " << mapit->first << "), intent " << PetscMemoryAccessModeToString(mapit->second.mode) << ' ' << it->frame();
    if (std::distance(it, end) == 0) oss << " (orphaned)"; // we were the only dependency
    oss << '\n';
    PetscFunctionReturn(0);
  }));
  PetscCheck(!wrote_to_oss, PETSC_COMM_SELF, PETSC_ERR_ORDER, "Destroying PetscDeviceContext ('%s', id %" PetscInt64_FMT ") would leave the following dangling (possibly orphaned) dependants:\n%s\nMust synchronize before destroying it, or allow it to be destroyed with orphans",
             PetscObjectCast(dctx)->name ? PetscObjectCast(dctx)->name : "unnamed", PetscObjectCast(dctx)->id, oss.str().c_str());
  PetscCall(CxxDataCast(dctx)->clear());
  PetscFunctionReturn(0);
}

template <bool use_debug>
static PetscErrorCode PetscDeviceContextMarkIntentFromID_Private(PetscDeviceContext dctx, PetscObjectId id, PetscMemoryAccessMode mode, PetscStackFrame<use_debug> frame, const char *name) {
#define DEBUG_INFO(mess, ...) PetscDebugInfo(dctx, "dctx %" PetscInt64_FMT " (%s) - obj %" PetscInt64_FMT " (%s): " mess, dctx_id, PetscObjectCast(dctx)->name ? PetscObjectCast(dctx)->name : "unnamed", id, name, ##__VA_ARGS__)
  const auto dctx_id             = PetscObjectCast(dctx)->id;
  auto      &marked              = marked_object_map.map[id];
  auto      &old_mode            = marked.mode;
  auto      &object_dependencies = marked.dependencies;

  PetscFunctionBegin;
  if ((mode == PETSC_MEMORY_ACCESS_READ) && (old_mode == mode)) {
    const auto end = object_dependencies.end();
    const auto it  = std::find_if(object_dependencies.begin(), end, [&](const MarkedObjectMap::snapshot_type &obj) { return obj.dctx_id() == dctx_id; });

    PetscCall(DEBUG_INFO("new mode (%s) COMPATIBLE with %s mode (%s), no need to serialize\n", PetscMemoryAccessModeToString(mode), PetscMemoryAccessModeToString(old_mode), object_dependencies.empty() ? "default" : "old"));
    if (it != end) {
      // we have been here before, all we must do is update our entry then we can bail
      PetscCall(DEBUG_INFO("found old self as dependency, updating\n"));
      PetscAssert(CxxDataCast(dctx)->deps.find(id) != CxxDataCast(dctx)->deps.end(), PETSC_COMM_SELF, PETSC_ERR_PLIB, "PetscDeviceContext %" PetscInt64_FMT " listed as dependency for object %" PetscInt64_FMT " (%s), but does not have the object in private dependency list!", dctx_id, id, name);

      it->frame() = std::move(frame);
      PetscCall(PetscDeviceContextRecordEvent_Private(dctx, it->event()));
      PetscFunctionReturn(0);
    }

    // we have not been here before, need to serialize with the last write event (if it exists)
    // and add ourselves to the dependency list
    if (const auto event = marked.last_write.event()) PetscCall(PetscDeviceContextWaitForEvent_Private(dctx, event));
  } else {
    // we are incompatible with the previous mode
    PetscCall(DEBUG_INFO("new mode (%s) NOT COMPATIBLE with %s mode (%s), serializing then clearing (%zu) %s\n", PetscMemoryAccessModeToString(mode), object_dependencies.empty() ? "default" : "old", PetscMemoryAccessModeToString(old_mode),
                         object_dependencies.size(), object_dependencies.size() == 1 ? "dependency" : "dependencies"));
    for (const auto &dep : object_dependencies) {
      if (dep.dctx_id() == dctx_id) {
        PetscCall(DEBUG_INFO("found old self as dependency, skipping\n"));
        continue;
      }
      PetscCall(PetscDeviceContextWaitForEvent_Private(dctx, dep.event()));
    }

    // if the previous mode wrote, bump it to the previous write spot
    if (PetscMemoryAccessWrite(old_mode)) {
      PetscAssert(object_dependencies.size() == 1, PETSC_COMM_SELF, PETSC_ERR_PLIB, "Can only have a single writer as dependency!");
      PetscCall(DEBUG_INFO("moving last write dependency (intent %s)\n", PetscMemoryAccessModeToString(old_mode)));
      // note the move around object_dependencies.back() not around event(), this is to enable
      // the rvalue event() overload
      marked.last_write = std::move(object_dependencies.back());
    }

    // clear out the old dependencies and update the mode, we are about to append ourselves
    object_dependencies.clear();
    old_mode = mode;
  }
  // become the new leaf by appending ourselves
  PetscCall(DEBUG_INFO("%s with intent %s\n", object_dependencies.empty() ? "dependency list is empty, creating new leaf" : "appending to existing leaves", PetscMemoryAccessModeToString(mode)));
  PetscCallCXX(object_dependencies.emplace_back(dctx, std::move(frame)));
  PetscCallCXX(CxxDataCast(dctx)->deps.emplace(id));
  PetscFunctionReturn(0);
#undef DEBUG_INFO
}

/*@C
  PetscDeviceContextMarkIntentFromID - Indicate a `PetscDeviceContext`s access intent to the
  auto-dependency system

  Not Collective

  Input Parameters:
+ dctx - The `PetscDeviceContext`
. id   - The `PetscObjectId` to mark
. mode - The desired access intent
- name - The object name (for debug purposes, ignored in optimized builds)

  Notes:
  This routine formally informs the dependency system that `dctx` will access the object
  represented by `id` with `mode` and adds `dctx` to `id`'s list of dependencies (termed
  "leaves").

  If the existing set of leaves have an incompatible `PetscMemoryAccessMode` to `mode`, `dctx`
  will be serialized against them.

  Level: intermediate

.seealso: `PetscDeviceContextWaitForContext()`, `PetscDeviceContextSynchronize()`,
`PetscObjectGetId()`, `PetscMemoryAccessMode`
@*/
PetscErrorCode PetscDeviceContextMarkIntentFromID(PetscDeviceContext dctx, PetscObjectId id, PetscMemoryAccessMode mode, const char name[]) {
#if PetscDefined(USE_DEBUG)
  const auto index    = petscstack.currentsize > 2 ? petscstack.currentsize - 2 : 0;
  const auto file     = petscstack.file[index];
  const auto function = petscstack.function[index];
  const auto line     = petscstack.line[index];
#else
  constexpr const char *file     = nullptr;
  constexpr const char *function = nullptr;
  constexpr auto        line     = 0;
#endif

  PetscFunctionBegin;
  PetscCall(PetscDeviceContextGetOptionalNullContext_Internal(&dctx));
  if (name) PetscValidCharPointer(name, 4);
  PetscCall(marked_object_map.register_finalize());
  PetscCall(PetscLogEventBegin(DCONTEXT_Mark, dctx, nullptr, nullptr, nullptr));
  PetscCall(PetscDeviceContextMarkIntentFromID_Private(dctx, id, mode, MarkedObjectMap::snapshot_type::frame_type{file, function, line}, name ? name : "unknown object"));
  PetscCall(PetscLogEventEnd(DCONTEXT_Mark, dctx, nullptr, nullptr, nullptr));
  PetscFunctionReturn(0);
}