Parfeval blocks parfor loop evaluation
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The existance of any parfeval job blocks the execution of a parfor loop. This occurs even when available pool workers are available, and should be free to execute the parfor loop.
On my machine, with 32 cores, running this:
function testParallelBlocking
nIter = 3;
pool = gcp;
j = parfeval(pool,@backgroundFcn,1);
for i = 1:nIter
forLoopTime(i) = now;
end
parfor i = 1:nIter
parforLoopTime(i) = now;
end
disp(['Parfeval completed at ' datestr(j.fetchOutputs,'HH:MM:SS:FFF')]);
for i = 1:nIter
disp(['For loop completed at ' datestr(forLoopTime(nIter),'HH:MM:SS:FFF')]);
end
for i = 1:nIter
disp(['Parfor loop completed at ' datestr(parforLoopTime(nIter),'HH:MM:SS:FFF')]);
end
end
function out = backgroundFcn
pause(5);
out = now;
end
produces this output:
Parfeval completed at 15:15:25:244
For loop completed at 15:15:20:232
For loop completed at 15:15:20:232
For loop completed at 15:15:20:232
Parfor loop completed at 15:15:25:269
Parfor loop completed at 15:15:25:269
Parfor loop completed at 15:15:25:269
showing that while the rest of the code continues to run, the parfor loop does not begin until the parfeval job has completed.
Is there any way to have the parfor loop execute while the parfeval job is also running in the background? I have tried limiting the number of parfeval workers by changing
parfor i = 1:nIter
to
parfor (i = 1:nIter,nWorkers)
where nWorkers < (number of cores - number of pending parfeval jobs) but it does not change the behavior.
Thanks for your help.
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采纳的回答
Edric Ellis
2019-6-3
This is expected behaviour. Unfortunately, there is currently no way to overlap parfeval and parfor. Your best bet is probably to adapt your parfor loop to use parfeval instead (I appreciate that this might not be terribly convenient).
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