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ParallelKernels
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ParallelKernels

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gives the list of running kernels available for parallel computing.

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ParallelKernels["prop"]

gives those running kernels that satisfy the given property.

Details

  • On a multicore computer, kernels are normally launched automatically when needed for a parallel computation.
  • All available kernels are by default used for all parallel computations.
  • The following properties can be used to select a subset of all running kernels:
  • Allall kernels
    "CloudKernels"all cloud kernels
    "LinkKernels"all link kernels
    "LocalKernels"all kernels running locally
    "LWGKernels"all LightweightGrid kernels
    "OneKernelPerMachine"one kernel for each different machine
    "RemoteKernels"all kernels on remote machines
    "SshKernels"all SSH kernels
    "WSTPServerKernels"all WSTPServer kernels

Examples

open allclose all

Basic Examples  (1)Summary of the most common use cases

The list of currently running parallel kernels:

In[1]:=1
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https://wolfram.com/xid/0n4mm4yu9no-c0eoty
Out[1]=1

Scope  (5)Survey of the scope of standard use cases

Launch the default set of kernels:

In[1]:=1
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https://wolfram.com/xid/0n4mm4yu9no-or7uha
Out[1]=1

Give the list of currently running parallel kernels:

In[2]:=2
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https://wolfram.com/xid/0n4mm4yu9no-jtvifu
Out[2]=2

Close all running parallel kernels:

In[3]:=3
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https://wolfram.com/xid/0n4mm4yu9no-c7abox
Out[3]=3

No kernels are running:

In[4]:=4
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https://wolfram.com/xid/0n4mm4yu9no-2tsh5
Out[4]=4

Launch kernels on various machines:

In[1]:=1
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https://wolfram.com/xid/0n4mm4yu9no-tqiiic
Out[1]=1

Select one kernel for each machine:

In[1]:=1
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https://wolfram.com/xid/0n4mm4yu9no-8jkzqw
Out[1]=1

Run an evaluation on this subset of kernels:

In[2]:=2
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https://wolfram.com/xid/0n4mm4yu9no-8e9o2n
Out[2]=2

Select all kernels of a particular type:

In[1]:=1
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https://wolfram.com/xid/0n4mm4yu9no-bgoh1d
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0n4mm4yu9no-v06x2o
Out[2]=2
In[3]:=3
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https://wolfram.com/xid/0n4mm4yu9no-qt64sr
Out[3]=3
In[4]:=4
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https://wolfram.com/xid/0n4mm4yu9no-knl5qe
Out[4]=4

Select all nonlocal kernels:

In[1]:=1
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https://wolfram.com/xid/0n4mm4yu9no-guffsg
Out[1]=1

Generalizations & Extensions  (1)Generalized and extended use cases

Remember the list of running kernels:

In[1]:=1
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https://wolfram.com/xid/0n4mm4yu9no-gakcs
Out[1]=1

Close all kernels:

In[2]:=2
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https://wolfram.com/xid/0n4mm4yu9no-bbt7ig
Out[2]=2

Launch copies of the previously running kernels:

In[3]:=3
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https://wolfram.com/xid/0n4mm4yu9no-h6g4x2
Out[3]=3

Properties & Relations  (2)Properties of the function, and connections to other functions

ParallelEvaluate by default does one evaluation on each kernel:

In[1]:=1
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https://wolfram.com/xid/0n4mm4yu9no-c3ihye
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0n4mm4yu9no-blyq9e
Out[2]=2

$KernelCount gives the number of running kernels:

In[1]:=1
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https://wolfram.com/xid/0n4mm4yu9no-x6lxb
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0n4mm4yu9no-npb76b
Out[2]=2
In[3]:=3
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https://wolfram.com/xid/0n4mm4yu9no-bgtdra
Out[3]=3

Possible Issues  (3)Common pitfalls and unexpected behavior

If no kernels are available, most parallel calculations are done sequentially:

In[1]:=1
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https://wolfram.com/xid/0n4mm4yu9no-7b004
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0n4mm4yu9no-f9yca5
Out[2]=2

A kernel launched as a remote kernel, but on the local machine, is treated as remote:

In[1]:=1
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https://wolfram.com/xid/0n4mm4yu9no-errbmo
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0n4mm4yu9no-inzrgq
Out[2]=2
In[3]:=3
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https://wolfram.com/xid/0n4mm4yu9no-te59v8
Out[3]=3

Earlier versions of the Wolfram Language provided this functionality under the name Kernels:

In[1]:=1
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https://wolfram.com/xid/0n4mm4yu9no-6n3ry
Out[1]=1

Neat Examples  (1)Surprising or curious use cases

Given multiple running kernels on many different machines:

In[1]:=1
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https://wolfram.com/xid/0n4mm4yu9no-bgh92b
Out[1]=1

Load a resource function into the cache on each machine only once:

In[2]:=2
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https://wolfram.com/xid/0n4mm4yu9no-0t9jlv
Out[2]=2

Use the resource function in all kernels:

In[3]:=3
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https://wolfram.com/xid/0n4mm4yu9no-ycqbdg
Out[3]=3
Wolfram Research (2022), ParallelKernels, Wolfram Language function, https://reference.wolfram.com/language/ref/ParallelKernels.html (updated 2022).
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Wolfram Research (2022), ParallelKernels, Wolfram Language function, https://reference.wolfram.com/language/ref/ParallelKernels.html (updated 2022).

Text

Wolfram Research (2022), ParallelKernels, Wolfram Language function, https://reference.wolfram.com/language/ref/ParallelKernels.html (updated 2022).

✖
Wolfram Research (2022), ParallelKernels, Wolfram Language function, https://reference.wolfram.com/language/ref/ParallelKernels.html (updated 2022).

CMS

Wolfram Language. 2022. "ParallelKernels." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2022. https://reference.wolfram.com/language/ref/ParallelKernels.html.

✖
Wolfram Language. 2022. "ParallelKernels." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2022. https://reference.wolfram.com/language/ref/ParallelKernels.html.

APA

Wolfram Language. (2022). ParallelKernels. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/ParallelKernels.html

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Wolfram Language. (2022). ParallelKernels. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/ParallelKernels.html

BibTeX

@misc{reference.wolfram_2025_parallelkernels, author="Wolfram Research", title="{ParallelKernels}", year="2022", howpublished="\url{https://reference.wolfram.com/language/ref/ParallelKernels.html}", note=[Accessed: 25-May-2025 ]}

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@misc{reference.wolfram_2025_parallelkernels, author="Wolfram Research", title="{ParallelKernels}", year="2022", howpublished="\url{https://reference.wolfram.com/language/ref/ParallelKernels.html}", note=[Accessed: 25-May-2025 ]}

BibLaTeX

@online{reference.wolfram_2025_parallelkernels, organization={Wolfram Research}, title={ParallelKernels}, year={2022}, url={https://reference.wolfram.com/language/ref/ParallelKernels.html}, note=[Accessed: 25-May-2025 ]}

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@online{reference.wolfram_2025_parallelkernels, organization={Wolfram Research}, title={ParallelKernels}, year={2022}, url={https://reference.wolfram.com/language/ref/ParallelKernels.html}, note=[Accessed: 25-May-2025 ]}