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WaitNext
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WaitNext

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WaitNext[{eid1,eid2,…}]

waits until the first evaluation represented by any of the eidi finishes, then returns its result, the corresponding eidi, and the list of remaining eidk.

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WaitNext[{eid1,eid2,…},h]

wraps the head h around the result before returning it.

Details

  • The eidi are EvaluationObject expressions obtained by submitting expressions for concurrent evaluation using ParallelSubmit.
  • WaitNext[{eid1,eid2,…}] returns a list {res,eid,eids}, where res is the result of the finished evaluation, eid is its EvaluationObject, and eids is the list of remaining evaluations.
  • The last element in the list produced by WaitNext is suitable for another call to WaitNext.

Examples

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

Submit a number of integer factorizations:

In[1]:=1
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https://wolfram.com/xid/0i1trmph2-i8liwy
Out[1]=1

Wait until the fastest one is done:

In[2]:=2
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https://wolfram.com/xid/0i1trmph2-hxvzo7
Out[2]=2

Wait for the next one:

In[3]:=3
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https://wolfram.com/xid/0i1trmph2-dg8r3c
Out[3]=3

Finally, wait for all remaining ones:

In[4]:=4
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https://wolfram.com/xid/0i1trmph2-cgq0hg
Out[4]=4

Scope  (1)Survey of the scope of standard use cases

Define a symbol only on the master kernel:

In[1]:=1
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https://wolfram.com/xid/0i1trmph2-6odhto

Submit a number of evaluations using this symbol:

In[2]:=2
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https://wolfram.com/xid/0i1trmph2-o47gjt

Return the first result:

In[3]:=3
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https://wolfram.com/xid/0i1trmph2-qy1ll4
Out[3]=3

Return the next result, but wrap it in Hold first:

In[4]:=4
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https://wolfram.com/xid/0i1trmph2-gjp4s3
Out[4]=4

Applications  (1)Sample problems that can be solved with this function

Test for primality, returning $Failed if it is not prime:

In[1]:=1
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https://wolfram.com/xid/0i1trmph2-d2vyth

Adaptively schedule search jobs until a result has been found or the computation is aborted:

In[2]:=2
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https://wolfram.com/xid/0i1trmph2-cly25c
In[3]:=3
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https://wolfram.com/xid/0i1trmph2-2iy37
Out[3]=3

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

ParallelTry is essentially implemented in terms of WaitNext:

In[1]:=1
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https://wolfram.com/xid/0i1trmph2-c22dap
In[2]:=2
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https://wolfram.com/xid/0i1trmph2-ferohc
Out[2]=2

Scheduled evaluations no longer needed can be aborted with AbortKernels:

In[1]:=1
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https://wolfram.com/xid/0i1trmph2-b1zabm
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0i1trmph2-njwgfp
Out[2]=2
In[3]:=3
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https://wolfram.com/xid/0i1trmph2-bn7sed

Possible Issues  (2)Common pitfalls and unexpected behavior

No more than $KernelCount evaluations are initially run to find the fastest one:

In[1]:=1
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https://wolfram.com/xid/0i1trmph2-bmgk95
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0i1trmph2-czr68
Out[2]=2
In[3]:=3
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https://wolfram.com/xid/0i1trmph2-5977r
Out[3]=3
In[4]:=4
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https://wolfram.com/xid/0i1trmph2-cqbbmw
Out[4]=4

Each evaluation should be waited for exactly once:

In[1]:=1
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https://wolfram.com/xid/0i1trmph2-dd9pc4
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0i1trmph2-depdbi
Out[2]=2

One of the evaluation objects has already completed:

In[3]:=3
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https://wolfram.com/xid/0i1trmph2-lkgklu
Out[3]=3
In[4]:=4
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https://wolfram.com/xid/0i1trmph2-cw72xi
Out[4]=4
Wolfram Research (2008), WaitNext, Wolfram Language function, https://reference.wolfram.com/language/ref/WaitNext.html.
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Wolfram Research (2008), WaitNext, Wolfram Language function, https://reference.wolfram.com/language/ref/WaitNext.html.

Text

Wolfram Research (2008), WaitNext, Wolfram Language function, https://reference.wolfram.com/language/ref/WaitNext.html.

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Wolfram Research (2008), WaitNext, Wolfram Language function, https://reference.wolfram.com/language/ref/WaitNext.html.

CMS

Wolfram Language. 2008. "WaitNext." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/WaitNext.html.

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Wolfram Language. 2008. "WaitNext." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/WaitNext.html.

APA

Wolfram Language. (2008). WaitNext. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/WaitNext.html

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Wolfram Language. (2008). WaitNext. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/WaitNext.html

BibTeX

@misc{reference.wolfram_2025_waitnext, author="Wolfram Research", title="{WaitNext}", year="2008", howpublished="\url{https://reference.wolfram.com/language/ref/WaitNext.html}", note=[Accessed: 01-April-2025 ]}

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@misc{reference.wolfram_2025_waitnext, author="Wolfram Research", title="{WaitNext}", year="2008", howpublished="\url{https://reference.wolfram.com/language/ref/WaitNext.html}", note=[Accessed: 01-April-2025 ]}

BibLaTeX

@online{reference.wolfram_2025_waitnext, organization={Wolfram Research}, title={WaitNext}, year={2008}, url={https://reference.wolfram.com/language/ref/WaitNext.html}, note=[Accessed: 01-April-2025 ]}

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@online{reference.wolfram_2025_waitnext, organization={Wolfram Research}, title={WaitNext}, year={2008}, url={https://reference.wolfram.com/language/ref/WaitNext.html}, note=[Accessed: 01-April-2025 ]}