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send

Send data from worker to client using a data queue

Syntax

send(queue, data)
send(pollablequeue, data)

Description

example

send(queue, data) sends a message or data with the value data to the parallel.pool.DataQueue specified by queue. Call afterEach to pass each of the pending messages to the function specified by afterEach.

example

send(pollablequeue, data) sends a message or data with the value data to the parallel.pool.PollableDataQueue specified by pollablequeue. Retrieve the result using poll(pollablequeue), and return data as the answer.

Use the send and poll functions together using a pollable data queue to transfer and retrieve messages or data from different workers.

Examples

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Construct a DataQueue, and call afterEach.

q = parallel.pool.DataQueue;
afterEach(q, @disp);
Start a parfor-loop, and send a message. The pending message is passed to the afterEach function, in this example @disp.

parfor i = 1:3
    send(q, i); 
end;
     1

     2

     3

For more details on listening for data using a DataQueue, see afterEach.

Construct a PollableDataQueue.

p = parallel.pool.PollableDataQueue;
Start a parfor-loop, and send a message, such as data with the value 1.
parfor i = 1
    send(p, i); 
end
Poll for the result.

poll(p)
     1

For more details on retrieving data using a PollableDataQueue, see poll.

This example shows a function that creates a parfor wait bar. Create a DataQueue, and use afterEach to specify the function to execute each time the queue receives data. This example calls a subfunction that updates the wait bar.

Create a parfor-loop to carry out a computationally demanding task in MATLAB®. Use send to send some dummy data on each iteration of the parfor-loop. When the queue receives the data, afterEach calls nUpdateWaitbar in the client MATLAB, and you can observe the wait bar progress.

function a = parforWaitbar

D = parallel.pool.DataQueue;
h = waitbar(0, 'Please wait ...');
afterEach(D, @nUpdateWaitbar);

N = 200;
p = 1;

parfor i = 1:N
    a(i) = max(abs(eig(rand(400))));
    send(D, i);
end

    function nUpdateWaitbar(~)
        waitbar(p/N, h);
        p = p + 1;
    end
end

Input Arguments

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Data queue, specified as a parallel.pool.DataQueue object.

Example: q = parallel.pool.DataQueue;

Message or data from workers to a data queue, specified as any data type that can be serialized.

Example: send(queue, data);

Pollable data queue, specified as a parallel.pool.PollableDataQueue object.

Example: p = parallel.pool.PollableDataQueue;

Introduced in R2017a

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