Re: [eigen] assembling a sparse matrix from multiple threads

Il giorno gio 5 lug 2018 alle ore 16:50 Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx> ha scritto:

On 2018-07-05 14:47, Andrea Bocci wrote:
> Yes, unfortunately: if I understand correctly how it works, a sparse matrix
> does not preallocate all its elements; they are allocated as the matrix is
> filled, and this part that is not safe for concurrent operations.

You can actually pre-allocate a sparse matrix (using
SparseMatrix::reserve():
http://eigen.tuxfamily.org/dox/classEigen_1_1SparseMatrix.html#ac2b219eb36fbab0bfae535cfbfc74a76

Even then (i.e., if you can guarantee that sufficiently many elements
are reserved per inner vector), insertion is still not completely
thread-safe, because elements can get moved, and the `m_data.m_size`
member variable will be modified by different threads -- you may get
lucky here, but you should really not rely on that.

Christoph

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Dr.-Ing. Christoph Hertzberg

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