On Sun, Mar 7, 2010 at 5:06 PM, Gokhan Sever <[email protected]> wrote:
> Parallel Python is a separate module. IPython is the interactive
> Python interpreter that comes with Sage. However to use the IPython
> parallel features you need to install some additional packages. I am
> not sure if you could get it work from within Sage. More recommended
> way is to have an external installation.
>
> I don't know about @parallel yet. Please do tell me and give an
> example of its usage. I look at the Parallel Python examples and they
> are all lengthy. multiprocessing provides much simpler solution at a
> first sight.
I wrote @parallel. Type
sage: parallel?
for some documentation and look at the source code in Sage.
You just do
@parallel(4)
def f(n):
# do some computation
then
for X in f([1..10]):
print X
and 4 copies of X will run at once.
The actual implementation is *very* simple compared to multiprocessing
or Parallel Python. It's about 2 pages of custom code I wrote from
scratch just using pure Python and the fork system call (which is part
of the os module). However, it has special support for forking Sage
itself -- there are a number of issues having to do with pexpect
interfaces, etc., which @parallel takes care of, but multiprocessing
or Parallel python wouldn't know about.
Another nice (imho) thing about @parallel is that it fork's a new
process for each evaluation of the function f. This is good because
(1) forking is cheap, (2) the entire *state* of your process is copied
to the forked processes as is (e.g., you can have @parallel's inside
of functions you define on the command line or notebook, etc.), (3) if
the computation of f(n) leaks memory or segfaults, the calling program
doesn't die.
I use @parallel constantly for my research.
-- William
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