Question

有两个任务。一个通过MPI进行通信，另一个通过一些有趣的事情。我使用mpi非阻塞调用，以便允许正在运行的线程在等待信息时执行其他任务。但这不起作用。

一些代码解释。如果您愿意，可以直接跳至代码。它创建两个过程。第一个进程将休眠10秒钟，然后通过阻塞调用发送一些数据。第二个过程（这是您感兴趣的过程）将创建两个具有共享整数（完成）的线程。一个任务将被实例化一次，而另一个任务将被实例化与线程数相同的次数（在本例中为2）。第一个任务将使用非阻塞调用接收数据，并且应屈服，以便正在运行的线程可以执行另一个任务（但这不会发生）。该任务仅由一个线程运行。第二项任务只是打印一些很酷的东西。两个线程都实例化了此任务。

代码如下：

if (rank == 0)
  {
    buffer[1000] = 5;
    sleep(10);
    printf("Process %d sent data\n", rank);
    MPI_Send(buffer, SIZE, MPI_DOUBLE, 1, 5, MPI_COMM_WORLD);
  }
  else if (rank == 1)
  {
#pragma omp parallel num_threads(2) shared (done)
    {
#pragma omp single nowait
      {
#pragma omp task
        {
          int flag = 0;
          printf("Thread %d is receiving data\n", omp_get_thread_num());
          MPI_Irecv(buffer, SIZE, MPI_DOUBLE, 0, 5, MPI_COMM_WORLD, &request);

          MPI_Test(&request, &flag, &status);
          while (flag == 0)
          {
            #pragma omp taskyield
            MPI_Test(&request, &flag, &status);
            printf("Thread %d is wasting time\n", omp_get_thread_num());
            sleep(1);
          }

          done=1;
          printf("Thread %d received data\n", omp_get_thread_num());
        }
      }

#pragma omp task 
      {
        printf("Thread %d entered to the cool task\n", omp_get_thread_num());
        while (done == 0)
        {
          printf("Thread %d is doing some cool stuff\n", omp_get_thread_num());
          sleep(1); /* Or not */
        }
      }
    }
  }

这是输出：

Thread 0 is receiving data
Thread 1 entered to the cool task
Thread 1 is doing some cool stuff
Thread 0 is wasting time
Thread 1 is doing some cool stuff
Thread 0 is wasting time
Thread 1 is doing some cool stuff
Thread 0 is wasting time
Thread 1 is doing some cool stuff
Thread 0 is wasting time
Thread 1 is doing some cool stuff
Thread 0 is wasting time
Thread 1 is doing some cool stuff
Thread 0 is wasting time
Thread 1 is doing some cool stuff
Thread 0 is wasting time
Thread 1 is doing some cool stuff
Thread 0 is wasting time
Thread 1 is doing some cool stuff
Thread 0 is wasting time
Thread 1 is doing some cool stuff
Thread 0 is wasting time
Process 0 sent data
Thread 1 is doing some cool stuff
Thread 0 is wasting time
Thread 1 is doing some cool stuff
Thread 0 is wasting time
Thread 1 is doing some cool stuff
Thread 0 received data
Thread 0 entered to the cool task

您可以看到，线程0直到完成通信任务后才进入酷任务。

编译命令：

mpicc -fopenmp pruebas.c -o prueba

执行命令：

mpirun -np 2 --allow-run-as-root ./prueba (worry not, read below)

其他信息：

The program is being ran in a docker container with ubuntu.
gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.10)
mpicc --show output: gcc -I/usr/lib/openmpi/include/openmpi/opal/mca/event/libevent2021/libevent -I/usr/lib/openmpi/include/openmpi/opal/mca/event/libevent2021/libevent/include -I/usr/lib/openmpi/include -I/usr/lib/openmpi/include/openmpi -pthread -Wl,-rpath -Wl,/usr/lib/openmpi/lib -Wl,--enable-new-dtags -L/usr/lib/openmpi/lib -lmpi

Answer 1

OpenMP规范不需要说taskyield做任何事情

taskyield构造指定可以暂停当前任务以便执行其他任务。

因此它允许进行重新安排，但不需要重新安排。（在这一点上，任务调度算法的描述也很清楚）。因此，gcc完全有权利不进行重新安排。

但是，我确实知道LLVM（和Intel）OpenMP运行时确实产生了，并且我们可以看到gcc is generating a call into the runtime，所以有可能仅将LLVM运行时与二进制文件一起使用就足够了。或者，尝试使用clang或the Intel compilers

（完全公开：我为Intel工作：-））

OPENMP taskyield指令未在混合（openmp + mpi）程序中产生任务

1 个答案: