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MathGroup Archive 2012

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Prevent synchronizing a certain symbol between main and parallel

  • To: mathgroup at smc.vnet.net
  • Subject: [mg124061] Prevent synchronizing a certain symbol between main and parallel
  • From: Szabolcs Horvát <szhorvat at gmail.com>
  • Date: Sat, 7 Jan 2012 05:23:37 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

Hello,

I am trying to use LibraryLink with remote parallel kernels.  I end up 
with a library function (let's call it libFun[]) that has a different 
value on the main and parallel kernels due to different paths on the two 
machines.

Unfortunately it is very easy to inadvertently synchronize the value of 
a symbol between the main and subkernels.  My question is about how I 
can ensure that this syncing will not happen for libFun[].


I'll show in an isolated example how this might accidentally happen:

In[1]:= LaunchKernels[2]
Out[1]= {KernelObject[1, "local"], KernelObject[2, "local"]}

Set value of x in main kernel:

In[2]:= x = 1
Out[2]= 1

Note that it gets the same value in remote kernels too:

In[3]:= ParallelEvaluate[x]
Out[3]= {1, 1}

Set a different value for x in the parallel kernels and verify that they 
keep it:

In[4]:= ParallelEvaluate[x = 2]
Out[4]= {2, 2}

In[5]:= {x, ParallelEvaluate[x]}
Out[5]= {1, {2, 2}}

Now "innocently" use Parallelize on something containing x:

In[6]:= Parallelize[Table[x, {10}]]
Out[6]= {1, 1, 1, 1, 1, 1, 1, 1, 1, 1}

And see how the value of x got re-synced between the main and subkernels.

In[7]:= {x, ParallelEvaluate[x]}
Out[7]= {1, {1, 1}}


So the question is:

How can I prevent a certain symbol from ever auto-syncing between the 
main and the subkernels?


Related: 
http://stackoverflow.com/questions/8718256/remote-parallel-kernels-and-librarylink-how-to-make-them-work-together


-- 
Szabolcs Horvát
Mma QA site proposal: http://area51.stackexchange.com/proposals/37304



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