[Swift-user] How to wait on functions that return no data?

[Michael Wilde]

 >> In the example below, I want collectResults() to get invoked after all
 >> the runam() calls complete in doall().
 >
 > results = doall();
 > collectResults(results);
 >
 > Mihael

But thats the problem: doall() does not in this example return results. 
If it would return an artificial result, how would we get such a return 
to wait until all the runam() calls made within the freach() have completed?

Each of the runam() call runs a small model, and in this proposed 
scenario would leave those results on a local disk for later collection, 
either in a single shared file that many invocations would append to, or 
in a set of files.

Then collectresults() would run a job that collects all the data when done.

One approach can be to have collectresults() just run iteratively until 
it has collected a sufficient number of results.  I.e., to have it not 
depend on swift to find out when all the runam() calls have completed. 
That might work.

- Mike


On 3/25/08 10:00 AM, Mihael Hategan wrote:
> On Tue, 2008-03-25 at 09:46 -0500, Michael Wilde wrote:
>> For the petro-model app Im working on, it would be interesting to run 
>> the parameter sweep in "map reduce" manner, in which each invocation 
>> bites off a portion of the parameter space and processes it, resulting 
>> in a set of result tuples. Each run of the model will produce a set of 
>> tuples, and when all are done, we want to aggregate and plot the tuples.
>>
>> While with batching this is not strictly needed, it would be interesting 
>> to let the model results accumulate on the local filesystem (as in this 
>> case they are small) and collect them either at the end of the run, or 
>> periodically and perhaps asynchronously during the run.
>>
>> To do this, we'd want to write the model invocation as a swift function 
>> with only scalar numeric parameters, and no output.
> 
> That assertion I'm not sure about.
> 
>> The question is how to call a zero-returns function in a swift foreach() 
>> loop, and embed that foreach() in a function that doesnt return until 
>> all members of the foreach() have been processed.
> 
> The very notion of "return" as it would appear in a strict language
> doesn't make much sense in Swift, so I'm not quite sure.
> 
>> I havent tried to code this yet, because I cant think of a way to 
>> express it in swift, due to the data-dependency semantics.
>>
>> In the example below, I want collectResults() to get invoked after all 
>> the runam() calls complete in doall().
> 
> results = doall();
> collectResults(results);
> 
> Mihael
> 
>> Anyone have any ideas?
>>
>> This is a low-priority question, just food for thought, as the batched 
>> way of running this parameter sweep should be straightforward and efficient.
>>
>> Mike
>>
>>
>>
>> // Amiga-Mars Parameter Sweep
>>
>> type amout;
>>
>> runam (string id , string p1, string p2) // no ret val
>> {
>>    app { runam3 id p1 p2 ; }
>> }
>>
>> type params {
>>    string id;
>>    string p1;
>>    string p2;
>> };
>>
>> doall(params p[])
>> {
>>    foreach pset in p {
>>      runam(pset.id, pset.p1, pset.p2);
>>    }
>>    // waitTillAllDone();
>>    // want to block here till all above finish,
>>    // but no data to wait on.  any way to
>>    // achieve this???
>> }
>>
>> // Main
>>
>> params p[];
>> p = readdata("paramlist");
>> doall(p);
>> amout amdata <some mapping>;
>> amdata = collectResults();
>>
>> // ^^^ Want collectresults to run AFTER all runam() calls finish
>> //     in the doall() function.
>>
>>
>>
>>
>>
>>
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> 
>