send

Send data between clients and workers using a data queue

Syntax

send(queue,data)

send(pollablequeue,data)

Description

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

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

Use the send and poll functions together with a pollable data queue to transfer and retrieve messages or data between the client and workers.

Examples

Send and Automatically Display Message

Create a DataQueue, and use afterEach to set up a callback function that displays data from the queue on the client.

q = parallel.pool.DataQueue;
afterEach(q,@disp);

Run a parfor-loop, and send a message to the queue. When the message arrives on the client, it is passed to the afterEach callback function, @disp.

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

     1

     2

     3

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

Send Message and Poll for Result

Create a PollableDataQueue object.

p = parallel.pool.PollableDataQueue;

Use parfeval to send a message, such as data with the value 1.

f = parfeval(@send,0,p,1);
wait(f);

Poll for the result.

poll(p)

 ans = 1

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

Create a Simple parfor Wait Bar Using DataQueue

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

queue — Data queue

parallel.pool.DataQueue

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

Example: q = parallel.pool.DataQueue;

data — Message or data

scalar | vector | matrix | array | string | character vector | serializable object

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

Example: send(queue,data);

pollablequeue — Pollable data queue

PollableDataQueue

Pollable data queue, specified as a PollableDataQueue object.

If you close a PollableDataQueue using the close function, you can no longer send data to the queue. Any attempt to send data to the queue results in an error. (since R2025a)

Example: p = parallel.pool.PollableDataQueue;

Extended Capabilities

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

Version History

Introduced in R2017a