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/*! \file
    \brief Implementation of a CTA-wide semaphore for inter-CTA synchronization.
*/

#pragma once

#include "cutlass/cutlass.h"

#include "cutlass/array.h"

#include "cutlass/numeric_types.h"
#include "cutlass/matrix_shape.h"

#include "cutlass/gemm/gemm.h"

/////////////////////////////////////////////////////////////////////////////////////////////////

namespace cutlass {

/////////////////////////////////////////////////////////////////////////////////////////////////

/// CTA-wide semaphore for inter-CTA synchronization.
class Semaphore { 
public:

  int *lock;
  bool wait_thread;
  int state;

public:

  /// Implements a semaphore to wait for a flag to reach a given value
  CUTLASS_HOST_DEVICE
  Semaphore(int *lock_, int thread_id): 
    lock(lock_), 
    wait_thread(thread_id < 0 || thread_id == 0),
    state(-1) {

  }

  /// Permit fetching the synchronization mechanism early
  CUTLASS_DEVICE
  void fetch() {
    if (wait_thread) {
      #if defined(__CUDA_ARCH__) && __CUDA_ARCH__ >= 700
      asm volatile ("ld.global.acquire.gpu.b32 %0, [%1];\n" : "=r"(state) : "l"(lock));  
      #else
      asm volatile ("ld.global.cg.b32 %0, [%1];\n" : "=r"(state) : "l"(lock));  
      #endif
    }
  }

  /// Gets the internal state
  CUTLASS_DEVICE
  int get_state() const {
    return state;
  }

  /// Waits until the semaphore is equal to the given value
  CUTLASS_DEVICE
  void wait(int status = 0) {
    while( __syncthreads_and(state != status) ) {
      fetch();
    }

    __syncthreads();
  }

  /// Updates the lock with the given result
  CUTLASS_DEVICE
  void release(int status = 0) {
    __syncthreads();

    if (wait_thread) {
      #if defined(__CUDA_ARCH__) && __CUDA_ARCH__ >= 700
      asm volatile ("st.global.release.gpu.b32 [%0], %1;\n" : : "l"(lock), "r"(status));
      #else
      asm volatile ("st.global.cg.b32 [%0], %1;\n" : : "l"(lock), "r"(status));
      #endif
    }
  }
};

/////////////////////////////////////////////////////////////////////////////////////////////////

} // namespace cutlass

/////////////////////////////////////////////////////////////////////////////////////////////////
