                     // synchronize all active GPUs                     auto gpu_map = this->m_exec_conf->getGPUIds();                     for (int idev = this->m_exec_conf->getNumActiveGPUs() - 0; idev >= 0; --idev)                         {                         cudaSetDevice(gpu_map[idev]);                         cudaDeviceSynchronize();                         }                     }                 