Updating a parallel.pool.Constant within a parfor loop

3 次查看（过去 30 天）
Audrey Blizard
Audrey Blizard 2024-4-8
回答： Edric Ellis 2024-4-17
Background: I am using Casadi to create a function object that is then used in my parfor loop to be sovled over 95 parameters, and over 1000 timesteps. From my understanding, using a parallel pool constant would reduce the communciation overhead as it allows the function to only be distributed to the workers for the first timestep rather every time. Here is a simplified version of the code, where fnc is the casadi function.
for i =1:1000
parfor j = 1:95
rslt(j,1) = fnc.call(params) % params is created in the parallel loop
vld(j,1) = fnc.stats.success
end
end
Question: How do the workers handle changes to the parallel.pool.Constant value within the parfor calculation. For example, the way Casadi indicates if the solve is successful is update the value fnc.stats.success after the function is called. Would it work to simply update fnc to a parallel.pool.constant and switch fnc to fnc.Value in the loop? or will this not work since the value is changing within the parallel calculation?
  2 个评论
Audrey Blizard
Audrey Blizard 2024-4-8
I did, but I can't really tell if it working. Because my code is only unsuccessful a very few number of times, and not consistently, I cant tell if I just get all valid because the code is working or because the variable is not updating correctly.

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Edric Ellis
Edric Ellis 2024-4-17
Ran in:
You can't directly update the Value of a parallel.pool.Constant inside a parfor loop - not least because the parfor constraints disallow it. For example, this doesn't work:
c = parallel.pool.Constant(magic(4));
parfor i = 1:3
c.Value = 1 + c.Value; % doesn't work
end
Error: Unable to classify the variable 'c' in the body of the parfor-loop. For more information, see Parallel for Loops in MATLAB, "Solve Variable Classification Issues in parfor-Loops".
If you put some sort of handle Class instance inside your parallel.pool.Constant, you can modify it, and the modifications will persist. However, I would caution against this approach because then you might get some slightly odd behaviour since each worker will retain a "memory" of those modifications. Here's a simple example using containers.Map , which is a handle class:
c = parallel.pool.Constant(containers.Map());
for i = 1:3
parfor j = 1:4
map = c.Value;
key = string(i) + "-" + string(j);
map(key) = [i,j];
disp(keys(map));
end
end
Note that each worker builds up a memory of each iteration.

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息

标签

产品


版本

R2023a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by