Fix in stable_distribute and stable_distribute_inplace #25
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when the total size is less than the number of processes. Also added a test that was failing before the fix.
asrivast28
commented
Mar 28, 2020
| @@ -111,15 +111,18 @@ void stable_distribute(_InIterator begin, _InIterator end, _OutIterator out, con | |||
| size_t prefix = mxx::exscan(local_size, comm); | |||
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prefix may be the same as total_size if the processes with rank lower than the current process have all the input elements.
asrivast28
commented
Mar 28, 2020
| std::vector<size_t> send_counts(comm.size(), 0); | ||
| blk_dist part(total_size, comm.size(), comm.rank()); | ||
| int first_p = part.rank_of(prefix); |
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This is the line that leads to an error if prefix is the same as the total_size.
asrivast28
commented
Mar 28, 2020
| size = 0; | ||
| } | ||
| // XXX: test_distribute fails with an assertion error in mxx::sort | ||
| // test_distribute<std::vector<int>>(size, gen, c); |
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This seems to fail with an assertion error in sample_distribute. Is that expected?
patflick
approved these changes
Mar 29, 2020
|
LGTM thanks |
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Problem: Currently, the
mxx::stable_distribute*functions may crash on a process with rank >= p if the input size on every process with rank >= p is zero and the global input size is less than the total number of processes. This is because the functions try to determine the index of the first element of the current partition using the result of themxx::exscanwhich leads to a divide by zero error in the functionmxx::partition::blk_dist_buf::rank_of.Solution: A process should try to compute its send counts only if the input size on the process is non-zero.
I have also added a test that was failing before the fix.