parfor fails with loop indices being uint64

Question

Eli4ph 2017-10-27

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/363559-parfor-fails-with-loop-indices-being-uint64

评论： Eli4ph 2018-1-23

Documentation on parfor says that the loop indices can be of type uint64.

But with the following code, parfor fails. Either setting N to uint64(100) or changing the type of N to double/uint32 makes the code work. Is this a bug?

N = uint64(50);
A = zeros(3,N);
parfor r = 1:N
  A(:,r) = rand(3,1);
end
% fail
N = uint64(100);
A = zeros(3,N);
parfor r = 1:N
  A(:,r) = rand(3,1);
end
% work
N = uint32(50);
A = zeros(3,N);
parfor r = 1:N
  A(:,r) = rand(3,1);
end
% work
N = 50;
A = zeros(3,N);
parfor r = 1:N
  A(:,r) = rand(3,1);
end
% work

The error report is

An UndefinedFunction error was thrown on the workers for 'A'.
This might be because the file containing 'A' is not
accessible on the workers.  Use addAttachedFiles(pool, files)
to specify the required files to be attached.  See the
documentation for 'parallel.Pool/addAttachedFiles' for more
details.
Caused by:
    Undefined function or variable 'A'.

4 个评论
显示 2更早的评论隐藏 2更早的评论

Jan 2017-10-27

在 MATLAB Online 中打开

The question is still not clear: What does "fail" and "work" exactly? Please post again:

N = uint64(50);
A = zeros(3,N);
parfor r = 1:N
  A(:,r) = rand(3,1);
end
% Does it work?
N = 50;
A = zeros(3,N);
parfor r = 1:N
  A(:,r) = rand(3,1);
end
% Does it work?

Which Matlab version are you using?

Rik 2017-10-27

在 MATLAB Online 中打开

On R2017b (on 64 bit W10), the code below results in the mentioned error as well.

N = uint64(100);
A = zeros(3,N);
parfor r = 1:N
A(:,r) = rand(3,1);
end

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Edric Ellis 2017-10-30

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/363559-parfor-fails-with-loop-indices-being-uint64#answer_288481

This is indeed a bug in the implementation of parfor. Thanks for reporting this, we'll endeavour to fix this in a future release of MATLAB / Parallel Computing Toolbox. For now, I'm afraid the only workaround is to avoid using uint64 loop bounds for parfor.

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Eli4ph 2018-1-23

Could you explain a bit more? Does this bug affect other functions provided by MATLAB, in particular integer arithmetic (plus/minus and multiplication/division/remainder). Due to this bug, I feel unsafe about doing things with integral type. However now I have to pass data from MATLAB to C++ MEX file. Sorry to bother you again.

请先登录，再进行评论。