/*************************************************************************
 * Copyright (c) 2015-2017, NVIDIA CORPORATION. All rights reserved.
 *
 * See LICENSE.txt for license information
 ************************************************************************/

#ifndef NCCL_H_
#define NCCL_H_

#include <cuda_runtime.h>
#include <cuda_fp16.h>

#define NCCL_MAJOR 2
#define NCCL_MINOR 1
#define NCCL_PATCH 4
#define NCCL_SUFFIX ""

#ifdef __cplusplus
extern "C" {
#endif

/* Opaque handle to communicator */
typedef struct ncclComm* ncclComm_t;

#define NCCL_UNIQUE_ID_BYTES 128
typedef struct { char internal[NCCL_UNIQUE_ID_BYTES]; } ncclUniqueId;

/* Error type */
typedef enum { ncclSuccess                 =  0,
               ncclUnhandledCudaError      =  1,
               ncclSystemError             =  2,
               ncclInternalError           =  3,
               ncclInvalidArgument         =  4,
               ncclInvalidUsage            =  5,
               ncclNumResults              =  6 } ncclResult_t;

/* Generates an Id to be used in ncclCommInitRank. ncclGetUniqueId should be
 * called once and the Id should be distributed to all ranks in the 
 * communicator before calling ncclCommInitRank. */
ncclResult_t  ncclGetUniqueId(ncclUniqueId* uniqueId);
ncclResult_t pncclGetUniqueId(ncclUniqueId* uniqueId);

/* Creates a new communicator (multi thread/process version).
 * rank must be between 0 and nranks-1 and unique within a communicator clique.
 * Each rank is associated to a CUDA device, which has to be set before calling
 * ncclCommInitRank.
 * ncclCommInitRank implicitly syncronizes with other ranks, so it must be 
 * called by different threads/processes or use ncclGroupStart/ncclGroupEnd. */
ncclResult_t  ncclCommInitRank(ncclComm_t* comm, int nranks, ncclUniqueId commId, int rank);
ncclResult_t pncclCommInitRank(ncclComm_t* comm, int nranks, ncclUniqueId commId, int rank);

/* Creates a clique of communicators (single process version).
 * This is a convenience function to create a single-process communicator clique.
 * Returns an array of ndev newly initialized communicators in comm.
 * comm should be pre-allocated with size at least ndev*sizeof(ncclComm_t).
 * If devlist is NULL, the first ndev CUDA devices are used.
 * Order of devlist defines user-order of processors within the communicator. */
ncclResult_t  ncclCommInitAll(ncclComm_t* comm, int ndev, const int* devlist);
ncclResult_t pncclCommInitAll(ncclComm_t* comm, int ndev, const int* devlist);

/* Frees resources associated with communicator object. */
ncclResult_t  ncclCommDestroy(ncclComm_t comm);
ncclResult_t pncclCommDestroy(ncclComm_t comm);

/* Returns a human-readable error message. */
const char*  ncclGetErrorString(ncclResult_t result);
const char* pncclGetErrorString(ncclResult_t result);

/* Gets the number of ranks in the communicator clique. */
ncclResult_t  ncclCommCount(const ncclComm_t comm, int* count);
ncclResult_t pncclCommCount(const ncclComm_t comm, int* count);

/* Returns the cuda device number associated with the communicator. */
ncclResult_t  ncclCommCuDevice(const ncclComm_t comm, int* device);
ncclResult_t pncclCommCuDevice(const ncclComm_t comm, int* device);

/* Returns the user-ordered "rank" associated with the communicator. */
ncclResult_t  ncclCommUserRank(const ncclComm_t comm, int* rank);
ncclResult_t pncclCommUserRank(const ncclComm_t comm, int* rank);

/* Reduction operation selector */
typedef enum { ncclSum        = 0,
               ncclProd       = 1,
               ncclMax        = 2,
               ncclMin        = 3,
               ncclNumOps     = 4 } ncclRedOp_t;

/* Data types */
typedef enum { ncclInt8       = 0, ncclChar       = 0,
               ncclUint8      = 1,
               ncclInt32      = 2, ncclInt        = 2,
               ncclUint32     = 3,
               ncclInt64      = 4,
               ncclUint64     = 5,
               ncclFloat16    = 6, ncclHalf       = 6,
               ncclFloat32    = 7, ncclFloat      = 7,
               ncclFloat64    = 8, ncclDouble     = 8,
               ncclNumTypes   = 9 } ncclDataType_t;

/*
 * Collective communication operations
 *
 * Collective communication operations must be called separately for each
 * communicator in a communicator clique.
 *
 * They return when operations have been enqueued on the CUDA stream.
 *
 * Since they may perform inter-CPU synchronization, each call has to be done
 * from a different thread or process, or need to use Group Semantics (see
 * below).
 */

/* 
 * Reduce
 *
 * Reduces data arrays of length count in sendbuff into recvbuff using op 
 * operation.
 * recvbuff may be NULL on all calls except for root device.
 * root is the rank (not the CUDA device) where data will reside after the
 * operation is complete.
 *
 * In-place operation will happen if sendbuff == recvbuff.
 */
ncclResult_t  ncclReduce(const void* sendbuff, void* recvbuff, size_t count, ncclDataType_t datatype,
    ncclRedOp_t op, int root, ncclComm_t comm, cudaStream_t stream);
ncclResult_t pncclReduce(const void* sendbuff, void* recvbuff, size_t count, ncclDataType_t datatype,
    ncclRedOp_t op, int root, ncclComm_t comm, cudaStream_t stream);

/* 
 * Broadcast
 *
 * Copies count values from root to all other devices.
 * root is the rank (not the CUDA device) where data resides before the 
 * operation is started.
 * 
 * This operation is implicitely in place.
 */
ncclResult_t  ncclBcast(void* buff, size_t count, ncclDataType_t datatype, int root,
    ncclComm_t comm, cudaStream_t stream);
ncclResult_t pncclBcast(void* buff, size_t count, ncclDataType_t datatype, int root,
    ncclComm_t comm, cudaStream_t stream);

/* 
 * All-Reduce
 *
 * Reduces data arrays of length count in sendbuff using op operation, and
 * leaves identical copies of result on each recvbuff.
 *
 * In-place operation will happen if sendbuff == recvbuff.
 */
ncclResult_t  ncclAllReduce(const void* sendbuff, void* recvbuff, size_t count,
    ncclDataType_t datatype, ncclRedOp_t op, ncclComm_t comm, cudaStream_t stream);
ncclResult_t pncclAllReduce(const void* sendbuff, void* recvbuff, size_t count,
    ncclDataType_t datatype, ncclRedOp_t op, ncclComm_t comm, cudaStream_t stream);

/* 
 * Reduce-Scatter
 *
 * Reduces data in sendbuff using op operation and leaves reduced result 
 * scattered over the devices so that recvbuff on rank i will contain the i-th
 * block of the result.
 * Assumes sendcount is equal to nranks*recvcount, which means that sendbuff 
 * should have a size of at least nranks*recvcount elements.
 *
 * In-place operations will happen if recvbuff == sendbuff + rank * recvcount.
 */
ncclResult_t  ncclReduceScatter(const void* sendbuff, void* recvbuff,
    size_t recvcount, ncclDataType_t datatype, ncclRedOp_t op, ncclComm_t comm,
    cudaStream_t stream);
ncclResult_t pncclReduceScatter(const void* sendbuff, void* recvbuff,
    size_t recvcount, ncclDataType_t datatype, ncclRedOp_t op, ncclComm_t comm,
    cudaStream_t stream);

/* 
 * All-Gather
 *
 * Each device gathers sendcount values from other GPUs into recvbuff,
 * receiving data from rank i at offset i*sendcount.
 * Assumes recvcount is equal to nranks*sendcount, which means that recvbuff
 * should have a size of at least nranks*sendcount elements.
 *
 * In-place operations will happen if sendbuff == recvbuff + rank * sendcount.
 */
ncclResult_t  ncclAllGather(const void* sendbuff, void* recvbuff, size_t sendcount,
    ncclDataType_t datatype, ncclComm_t comm, cudaStream_t stream);
ncclResult_t pncclAllGather(const void* sendbuff, void* recvbuff, size_t sendcount,
    ncclDataType_t datatype, ncclComm_t comm, cudaStream_t stream);

/*
 * Group semantics
 *
 * When managing multiple GPUs from a single thread, and since NCCL collective 
 * calls may perform inter-CPU synchronization, we need to "group" calls for 
 * different ranks/devices into a single call.
 *
 * Grouping NCCL calls as being part of the same collective operation is done
 * using ncclGroupStart and ncclGroupEnd. ncclGroupStart will enqueue all 
 * collective calls until the ncclGroupEnd call, which will wait for all calls
 * to be complete. Note that for collective communication, ncclGroupEnd only 
 * guarantees that the operations are enqueued on the streams, not that
 * the operation is effectively done.
 *
 * Both collective communication and ncclCommInitRank can be used in conjunction
 * of ncclGroupStart/ncclGroupEnd.
 */

/*
 * Group Start
 *
 * Start a group call. All subsequent calls to NCCL may not block due to
 * inter-CPU synchronization.
 */
ncclResult_t ncclGroupStart();

/* 
 * Group End
 *
 * End a group call. Wait for all calls since ncclGroupStart to complete 
 * before returning.
 */
ncclResult_t ncclGroupEnd();

#ifdef __cplusplus
} // end extern "C"
#endif

#endif // end include guard

