MATLAB: How to use event listners for notifications sent from parfeval functions

event listnersnotifyparfeval

Is it possible to trigger a notify event from a parfeval function with a listner in the calling client? So far my experiments with this have failed (but without telling me about any errors.)

Best Answer

There currently isn't any support for events from parfeval futures. What sort of event support were you hoping for? Just a completion event?

For now, your best bet is call fetchNext in a loop, possibly with a timeout - although of course this doesn't give you the full flexibility that an event would.

Related Solutions

MATLAB: Error when Trying to use Listner Blocks

Try changing:

    set_param('manualflight','StartFcn',localAddEventListener);

To:

    set_param('manualflight','StartFcn','localAddEventListener');

StartFcn needs to be set to a string containing the MATLAB code to be executed. In the first case, the SET_PARAM function is trying to run the function localAddEventListener, with the expectation that it will return a string that must then be set as StartFcn. So the add_exec_event_listener call is made at the time that the set_param command is run, instead of when the model starts executing.

MATLAB: How to send data on the fly to a worker when using parfeval

I think it's possible to do this sort of thing by getting the workers to create a parallel.pool.PollableDataQueue, and getting the client to send messages to the worker. It's a bit awkward to set up, and in the example below, I'm going to use a parallel.pool.Constant to get the worker to hold onto the queue instance.

The general plan is this:

Get the worker to construct a pollable dataqueue
Send the dataqueue instance back to the client
Set the worker off into an loop waiting for messages from the client
Send messages from the client to get the worker to do stuff
When done, get the client to send a "poison pill" which gets the worker to return the result.

Note the code below only works for a pool of size 1. To run on a larger pool, you would need to use parfevalOnAll rather than parfeval, and you'd also need to manage the multiple queues from the workers.

% First, create a parallel pool if necessary
if isempty(gcp())
    parpool('local', 1);
end
% Get the worker to construct a data queue on which it can receive
% messages from the client
workerQueueConstant = parallel.pool.Constant(@parallel.pool.PollableDataQueue);
% Get the worker to send the queue object back to the client
workerQueueClient = fetchOutputs(parfeval(@(x) x.Value, 1, workerQueueConstant));
% Get the worker to start waiting for messages
future = parfeval(@doStuff, 1, workerQueueConstant);
% Send a few messages to the worker
for idx = 1:10
    send(workerQueueClient, idx);
end
% Send [] as a "poison pill" to the worker to get it to stop
send(workerQueueClient, []);
% Get the result
fetchOutputs(future)
% This function gets the worker to keep processing messages from the client
function out = doStuff(qConstant)
q = qConstant.Value;
out = 0;
while true
    % Wait for a message
    data = poll(q, Inf);
    if isempty(data)
        return
    else
        out = out + data;
    end
end
end

Best Answer

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MATLAB: Error when Trying to use Listner Blocks

MATLAB: How to send data on the fly to a worker when using parfeval

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