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ProcessGroup.hpp
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ProcessGroup.hpp
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#pragma once
#include <condition_variable>
#include <memory>
#include <mutex>
#include <stdexcept>
#include <unordered_map>
#include <vector>
#include <ATen/ATen.h>
#include <c10d/Types.hpp>
// *************************************************************************
// PROCESS GROUP collective communication API IS BEING CHANGED BETWEEN
// versions 1.7 and 1.8.
// PLEASE DO NOT ADD ANY DEPENDENCIES.
// SEE RFC: https://github.com/pytorch/pytorch/issues/39662
// *************************************************************************
constexpr auto kNoTimeout = std::chrono::milliseconds(0);
namespace c10d {
enum class OpType : std::uint8_t {
BROADCAST = 0,
ALLREDUCE = 1,
ALLREDUCE_COALESCED = 2,
REDUCE = 3,
ALLGATHER = 4,
ALLGATHER_BASE = 5,
ALLGATHER_COALESCED = 6,
GATHER = 7,
SCATTER = 8,
REDUCE_SCATTER = 9,
ALLTOALL_BASE = 10,
ALLTOALL = 11,
SEND = 12,
RECV = 13,
RECVANYSOURCE = 14,
BARRIER = 15,
UNKNOWN = 100,
};
const std::string GLOO_BACKEND_NAME = "gloo";
const std::string NCCL_BACKEND_NAME = "nccl";
const std::string MPI_BACKEND_NAME = "mpi";
const std::string ROUND_ROBIN_BACKEND_NAME = "round_robin";
const std::string UNDEFINED = "undefined";
// Converts OpType to human readable string.
std::string opTypeToString(OpType opType);
// Whether or not an OP is an p2p op (SEND, RECV, RECVANYSOURCE)
bool isP2POp(OpType opType);
// ProcessGroup is a base class that captures collective and point to
// point communication in a fixed set of processes.
//
// The functions specified in the class below describe the API alone;
// implementations are provided in subclasses.
//
// Every function that performs I/O is executed asynchronously by a
// thread pool owned by the ProcessGroup (by default). They return an
// object that can be used to wait for completion or error.
//
// The ProcessGroup can instantiate subgroups with fewer or an equal
// number of members. Implementations must take care that multiple
// process groups can be used in parallel and synchronize accordingly.
//
// The ProcessGroup assumes a fixed set of processes. If the set
// changes, existing instances must be destructed and instantiation
// and initialization must start from scratch. For members of the
// process group to find each other (referred to as rendezvous from
// hereon)
//
class ProcessGroup : public torch::CustomClassHolder {
public:
// Please do not use ProcessGroup::Work API, it is going away, to be
// replaced by ivalue::Future.
// Python binding for this class might change, please do not assume
// this will be bound using pybind.
class Work : public torch::CustomClassHolder {
public:
Work(int rank = -1, OpType opType = OpType::UNKNOWN, const char* profilingTitle = nullptr);
virtual ~Work();
// Checks if request has completed. Non-blocking operation.
virtual bool isCompleted();
// Returns if the work completed successfully.
// If false, the exception function can be called to get details.
virtual bool isSuccess() const;
// Returns exception if isSuccess() returned false.
virtual std::exception_ptr exception() const;
// Returns source rank if this objects represents a recv-from-any.
virtual int sourceRank() const;
// Returns result tensors, if applicable.
virtual std::vector<at::Tensor> result();
// Ensures that operations on the output tensors that are invoked
// after this function returns are correctly sequenced after the
// asynchronous completion of this work.
//
// For CUDA tensors, it inserts stream synchronization such that
// the streams of the caller wait for completion of the
// asynchronous operations on the destination tensors.
//
// For CPU tensors, it is currently a nop.
//
// This function should only be used if the caller polls for
// completion through the `isCompleted` function, it has returned
// true, and the `isSuccess` function also has returned true.
//
virtual void synchronize();
// Waits until request completes. Blocking operation.
// Throws if the work completed with an exception.
// Returns false if the work is aborted.
// Otherwise, it always returns true, indicating the work is completed.
//
// Functionally equivalent to:
//
// while (!isCompleted()) { /* nop */ }
// auto success = isSuccess();
// if (!success) { std::rethrow_exception(exception()); }
// return success;
//
virtual bool wait(std::chrono::milliseconds timeout = kNoTimeout);
virtual void abort();
// Returns a Future object that will be associated with the completion of
// work. Only NCCL backend is currently supported.
virtual c10::intrusive_ptr<c10::ivalue::Future> getFuture();
OpType retrieveOpType();
protected:
// Completes the work object and optionally sets the exception in a
// thread-safe manner. Notifies all waiting condition variables as well.
void finish(std::exception_ptr exception = nullptr);
// Similar to finish, but throws an exception if one is already set or
// provided by the user.
void finishAndThrow(std::exception_ptr exception);
mutable std::mutex mutex_;
std::condition_variable cv_;
bool completed_ = false;
std::exception_ptr exception_;
// Current rank of the node.
const int rank_;
// Operation type that this work object refers to.
OpType opType_;
// When profiling, the callback to record end of operation event. This
// callback needs to be called when collective operation is complete.
std::function<void()> recordFunctionEndCallback_;
};
explicit ProcessGroup(int rank, int size);
virtual ~ProcessGroup();
int getRank() const {
return rank_;
}
int getSize() const {
return size_;
}
virtual const std::string getBackendName() const {
return UNDEFINED;
}
virtual c10::intrusive_ptr<ProcessGroup::Work> broadcast(
std::vector<at::Tensor>& data,
const BroadcastOptions& opts = BroadcastOptions()) = 0;
virtual c10::intrusive_ptr<ProcessGroup::Work> allreduce(
std::vector<at::Tensor>& data,
const AllreduceOptions& opts = AllreduceOptions()) = 0;
// This will be moved out of ProcessGroup, do not add dependencies on this
// function.
virtual c10::intrusive_ptr<ProcessGroup::Work> allreduce_coalesced(
std::vector<at::Tensor>& tensors,
const AllreduceCoalescedOptions& opts = AllreduceCoalescedOptions()) = 0;
virtual c10::intrusive_ptr<ProcessGroup::Work> reduce(
std::vector<at::Tensor>& tensors,
const ReduceOptions& opts = ReduceOptions()) = 0;
virtual c10::intrusive_ptr<ProcessGroup::Work> allgather(
std::vector<std::vector<at::Tensor>>& outputTensors,
std::vector<at::Tensor>& inputTensors,
const AllgatherOptions& opts = AllgatherOptions()) = 0;
// Gathers a single tensor inputBuffer into a single buffer outputBuffer that
// is interpreted as a contigious collection of size inputBuffer * WORLD_SIZE.
// For implementers of ProcessGroup API and advanced users only.
virtual c10::intrusive_ptr<ProcessGroup::Work> allgather_base(
at::Tensor& outputBuffer,
at::Tensor& inputBuffer,
const AllgatherOptions& opts = AllgatherOptions()) = 0;
// This function is deprecated and will be moved out of ProcessGroup to comms:
// * do not add dependencies on this function,
// * do not implement it in your ProcessGroup, implement allgather_base
// instead.
virtual c10::intrusive_ptr<ProcessGroup::Work> allgather_coalesced(
std::vector<std::vector<at::Tensor>>& outputTensorLists,
std::vector<at::Tensor>& inputTensors,
const AllgatherOptions& opts = AllgatherOptions());
virtual c10::intrusive_ptr<ProcessGroup::Work> gather(
std::vector<std::vector<at::Tensor>>& outputTensors,
std::vector<at::Tensor>& inputTensors,
const GatherOptions& opts = GatherOptions()) = 0;
virtual c10::intrusive_ptr<ProcessGroup::Work> scatter(
std::vector<at::Tensor>& outputTensors,
std::vector<std::vector<at::Tensor>>& inputTensors,
const ScatterOptions& opts = ScatterOptions()) = 0;
virtual c10::intrusive_ptr<ProcessGroup::Work> reduce_scatter(
std::vector<at::Tensor>& outputTensors,
std::vector<std::vector<at::Tensor>>& inputTensors,
const ReduceScatterOptions& opts = ReduceScatterOptions()) = 0;
virtual c10::intrusive_ptr<ProcessGroup::Work> alltoall_base(
at::Tensor& outputTensor,
at::Tensor& inputTensor,
std::vector<int64_t>& outputSplitSizes,
std::vector<int64_t>& inputSplitSizes,
const AllToAllOptions& opts = AllToAllOptions()) {
throw std::runtime_error("ProcessGroup does not support alltoall");
}
virtual c10::intrusive_ptr<ProcessGroup::Work> alltoall(
std::vector<at::Tensor>& outputTensors,
std::vector<at::Tensor>& inputTensors,
const AllToAllOptions& opts = AllToAllOptions()) {
throw std::runtime_error("ProcessGroup does not support alltoall");
}
virtual c10::intrusive_ptr<ProcessGroup::Work> send(
std::vector<at::Tensor>& tensors,
int dstRank,
int tag) = 0;
virtual c10::intrusive_ptr<ProcessGroup::Work> recv(
std::vector<at::Tensor>& tensors,
int srcRank,
int tag) = 0;
virtual c10::intrusive_ptr<ProcessGroup::Work> recvAnysource(
std::vector<at::Tensor>& tensors,
int tag) = 0;
virtual c10::intrusive_ptr<ProcessGroup::Work> barrier(
const BarrierOptions& opts = BarrierOptions()) = 0;
protected:
const int rank_;
const int size_;
};
} // namespace c10d