[Python-ideas] solving multi-core Python
sturla.molden at gmail.com
Thu Jun 25 02:45:24 CEST 2015
On 25/06/15 02:09, Devin Jeanpierre wrote:
> Although, threads are better for memory
> usage, by defaulting to sharing even on write. (Good for memory, maybe
> not so good for bug-freedom...)
I am not sure. Code written to use OpenMP tend to have less bugs than
code written to use MPI. This suggests that shared memory is easier than
message-passing, which is contrary to the common belief.
My own experience with OpenMP and MPI suggests it is easier to create a
deadlock with message-passing than accidentally have threads access the
same address concurrently. This is also what I hear from other people
who writes code for scientific computing.
I see a lot of claims that message-passing is supposed to be "safer"
than a shared memory model, but that is not what we see with OpenMP and
MPI. With MPI, the programmer must make sure that the send and receive
commands are passed in the right order at the right time, in each
process. This leaves plenty of room for messing up or creating
unmaintainable spaghetti code, particularly in a complex algorithm. It
is easier to make sure all shared objects are protected with mutexes
than to make sure a spaghetti of send and receive messages are in
It might be that Python's queue method of passing messages leave less
room for deadlocking than the socket-like MPI_send and MPI_recv
functions. But I think message-passing are sometimes overrated as "the
safe solution" to multi-core programming (cf. Go and Erlang).
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