grid_barrier.cuh

File members: /home/runner/work/cccl/cccl/cub/cub/grid/grid_barrier.cuh
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 * Copyright (c) 2011, Duane Merrill.  All rights reserved.
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#pragma once

#include <cub/config.cuh>

#if defined(_CCCL_IMPLICIT_SYSTEM_HEADER_GCC)
#  pragma GCC system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_CLANG)
#  pragma clang system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_MSVC)
#  pragma system_header
#endif // no system header

#include <cub/thread/thread_load.cuh>
#include <cub/util_debug.cuh>

CUB_NAMESPACE_BEGIN

class GridBarrier
{
protected:
  using SyncFlag = unsigned int;

  // Counters in global device memory
  SyncFlag* d_sync;

public:
  GridBarrier()
      : d_sync(nullptr)
  {}

  _CCCL_DEVICE _CCCL_FORCEINLINE void Sync() const
  {
    volatile SyncFlag* d_vol_sync = d_sync;

    // Threadfence and syncthreads to make sure global writes are visible before
    // thread-0 reports in with its sync counter
    __threadfence();
    CTA_SYNC();

    if (blockIdx.x == 0)
    {
      // Report in ourselves
      if (threadIdx.x == 0)
      {
        d_vol_sync[blockIdx.x] = 1;
      }

      CTA_SYNC();

      // Wait for everyone else to report in
      for (int peer_block = threadIdx.x; peer_block < gridDim.x; peer_block += blockDim.x)
      {
        while (ThreadLoad<LOAD_CG>(d_sync + peer_block) == 0)
        {
          __threadfence_block();
        }
      }

      CTA_SYNC();

      // Let everyone know it's safe to proceed
      for (int peer_block = threadIdx.x; peer_block < gridDim.x; peer_block += blockDim.x)
      {
        d_vol_sync[peer_block] = 0;
      }
    }
    else
    {
      if (threadIdx.x == 0)
      {
        // Report in
        d_vol_sync[blockIdx.x] = 1;

        // Wait for acknowledgment
        while (ThreadLoad<LOAD_CG>(d_sync + blockIdx.x) == 1)
        {
          __threadfence_block();
        }
      }

      CTA_SYNC();
    }
  }
};

class GridBarrierLifetime : public GridBarrier
{
protected:
  // Number of bytes backed by d_sync
  size_t sync_bytes;

public:
  GridBarrierLifetime()
      : GridBarrier()
      , sync_bytes(0)
  {}

  cudaError_t HostReset()
  {
    cudaError_t retval = cudaSuccess;
    if (d_sync)
    {
      retval = CubDebug(cudaFree(d_sync));
      d_sync = nullptr;
    }
    sync_bytes = 0;
    return retval;
  }

  virtual ~GridBarrierLifetime()
  {
    HostReset();
  }

  cudaError_t Setup(int sweep_grid_size)
  {
    cudaError_t retval = cudaSuccess;
    do
    {
      size_t new_sync_bytes = sweep_grid_size * sizeof(SyncFlag);
      if (new_sync_bytes > sync_bytes)
      {
        if (d_sync)
        {
          retval = CubDebug(cudaFree(d_sync));
          if (cudaSuccess != retval)
          {
            break;
          }
        }

        sync_bytes = new_sync_bytes;

        // Allocate and initialize to zero
        retval = CubDebug(cudaMalloc((void**) &d_sync, sync_bytes));
        if (cudaSuccess != retval)
        {
          break;
        }

        retval = CubDebug(cudaMemset(d_sync, 0, new_sync_bytes));
        if (cudaSuccess != retval)
        {
          break;
        }
      }
    } while (0);

    return retval;
  }
};

CUB_NAMESPACE_END