MPI提供了四个不同级别的线程支持:MPI_THREAD_SINGLE，MPI_THREAD_SERIALIZED，MPI_THREAD_FUNNELED和MPI_THREAD_MULTIPLE.为了能够同时从不同的线程进行MPI调用，您必须使用MPI_THREAD_MULTIPLE线程支持级别初始化MPI，并确保该库实际上提供了该级别:

MPI provides four different levels of thread support: MPI_THREAD_SINGLE, MPI_THREAD_SERIALIZED, MPI_THREAD_FUNNELED, and MPI_THREAD_MULTIPLE. In order to be able to make MPI calls from different threads concurrently, you have to initialise MPI with the MPI_THREAD_MULTIPLE level of thread support and make sure that the library actually provides that level:

int provided;

MPI_Init_thread(&argc, &argv, MPI_THREAD_MULTIPLE, &provided);
if (provided < MPI_THREAD_MULTIPLE)
{
   printf("Error: the MPI library doesn't provide the required thread level\n");
   MPI_Abort(MPI_COMM_WORLD, 0);
}

如果您调用MPI_Init而不是MPI_Init_thread，则库可以***选择其创建者认为***的默认线程支持级别.对于MPI_THREAD_SINGLE的Open MPI，即不支持线程.您可以通过设置环境变量OMPI_MPI_THREAD_LEVEL来控制默认级别，但是不建议这样做-应该使用MPI_Init_thread.

If you call MPI_Init instead of MPI_Init_thread, the library is free to chose whatever default thread support level its creators deemed best. For Open MPI that is MPI_THREAD_SINGLE, i.e. no support for threads. You can control the default level by setting the environment variable OMPI_MPI_THREAD_LEVEL but that is not recommended - MPI_Init_thread should be used instead.