为什么我要打电话给MPI。析构函数中的Finalize（）？

Question

我目前正在尝试理解mpi4py。我设置了mpi4py.rc.initialize=False和mpi4py.rc.finalize=False，因为我不明白为什么我们想要自动初始化和终结。默认行为是在导入MPI时调用MPI. Init（）。我认为这样做的原因是，对于每个等级，都运行了一个python解释器实例，每个实例都将运行整个脚本，但这只是猜测。最后，我喜欢把它说清楚。

现在这引入了一些问题。我有这个密码

import numpy as np
import mpi4py
mpi4py.rc.initialize = False  # do not initialize MPI automatically
mpi4py.rc.finalize = False # do not finalize MPI automatically

from mpi4py import MPI # import the 'MPI' module
import h5py

class DataGenerator:
    def __init__(self, filename, N, comm):
        self.comm = comm
        self.file = h5py.File(filename, 'w', driver="mpio", comm=comm)

        # Create datasets
        self.data_ds= self.file.create_dataset("indices", (N,1), dtype='i')

    def __del__(self):
        self.file.close()
        

if __name__=='__main__':
    MPI.Init()
    world = MPI.COMM_WORLD
    world_rank = MPI.COMM_WORLD.rank

    filename = "test.hdf5"
    N = 10
    data_gen = DataGenerator(filename, N, comm=world)

    MPI.Finalize()

导致

$ mpiexec -n 4 python test.py 
*** The MPI_Barrier() function was called after MPI_FINALIZE was invoked.
*** This is disallowed by the MPI standard.
*** Your MPI job will now abort. [eu-login-04:01559] Local abort after MPI_FINALIZE started completed successfully, but am not able to aggregate error messages, and not able to guarantee that all other processes were killed!
*** The MPI_Barrier() function was called after MPI_FINALIZE was invoked.
*** This is disallowed by the MPI standard.
*** Your MPI job will now abort. [eu-login-04:01560] Local abort after MPI_FINALIZE started completed successfully, but am not able to aggregate error messages, and not able to guarantee that all other processes were killed!
-------------------------------------------------------------------------- Primary job  terminated normally, but 1 process returned a non-zero exit code. Per user-direction, the job has been aborted.
--------------------------------------------------------------------------
*** The MPI_Barrier() function was called after MPI_FINALIZE was invoked.
*** This is disallowed by the MPI standard.
*** Your MPI job will now abort. [eu-login-04:01557] Local abort after MPI_FINALIZE started completed successfully, but am not able to aggregate error messages, and not able to guarantee that all other processes were killed!
-------------------------------------------------------------------------- mpiexec detected that one or more processes exited with non-zero status, thus causing the job to be terminated. The first process to do so was:

  Process name: [[15050,1],3]   Exit code:    1
--------------------------------------------------------------------------

我对这里发生的事情有点困惑。如果我移动MPI。Finalize（）在析构函数的末尾，它可以正常工作。

并不是说我也使用h5py，它使用MPI进行并行化。我这里有一个并行文件IO。并不是说h5py需要使用MPI支持进行编译。您可以通过设置虚拟环境并运行pip安装--no binary=h5py h5py轻松实现这一点。

Answer 1

按照您编写的方式，data\u-gen将一直存在，直到主函数返回。但是你调用MPI。在函数内完成。因此，析构函数在finalize之后运行。h5py。文件close方法似乎调用了MPI。内部通信屏障。禁止在完成后调用此命令。

如果您希望有显式的控制，请确保在调用MPI. Finize之前销毁所有对象。当然，如果某些对象只被垃圾收集器而不是引用计数器销毁，即使这样也可能不够。

要避免这种情况，请使用上下文管理器而不是析构函数。

class DataGenerator:
    def __init__(self, filename, N, comm):
        self.comm = comm
        self.file = h5py.File(filename, 'w', driver="mpio", comm=comm)

        # Create datasets
        self.data_ds= self.file.create_dataset("indices", (N,1), dtype='i')

    def __enter__(self):
        return self

    def __exit__(self, type, value, traceback):
        self.file.close()


if __name__=='__main__':
    MPI.Init()
    world = MPI.COMM_WORLD
    world_rank = MPI.COMM_WORLD.rank

    filename = "test.hdf5"
    N = 10
    with DataGenerator(filename, N, comm=world) as data_gen:
        pass
    MPI.Finalize()