PollableDataQueue - Send and manually retrieve data - MATLAB (original) (raw)

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parallel.pool.PollableDataQueue

Send and manually retrieve data

Description

Use a PollableDataQueue object to send data from a function that you run in the background or in your current MATLAB® session.

You can send data from a function that you run on a parallel pool if you have Parallel Computing Toolbox™. For details, see parallel.pool.PollableDataQueue (Parallel Computing Toolbox).

When you create a PollableDataQueue object, you create a connection to the current MATLAB session that you can use to send and receive messages.

• To send data to the current MATLAB session, use send.
• To manually retrieve data after it is received in the current MATLAB session, use poll.

Creation

Syntax

Description

`q` = parallel.pool.PollableDataQueue creates an object that can be used to send and manually retrieve messages.

example

Properties

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QueueLength — Number of items waiting to be removed from queue

zero or positive integer

This property is read-only.

Number of items of data waiting to be removed from the queue, specified as a zero or positive integer.

• The value is a zero or positive integer in the MATLAB session that creates the PollableDataQueue object.
• Everywhere else, the value is 0.

For example, if you create a PollableDataQueue object in the current MATLAB session, you can run a function in the background with thatPollableDataQueue object as an input argument. TheQueueLength property of that PollableDataQueue object will always be 0 in the background.

Object Functions

Examples

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Manually Retrieve Data Sent from the Background

This example shows how to manually retrieve data in your current MATLAB session that you send from the background.

Create a PollableDataQueue object.

q = parallel.pool.PollableDataQueue;

The helper function magicWithSend defined at the end of this example sends the sum of a magic square to a DataQueue or PollableDataQueue object, then returns that magic square.

Use parfeval and backgroundPool to run the function magicWithSend in the background.

f = parfeval(backgroundPool,@magicWithSend,1,q,3);

To retrieve the output from the background, use fetchOutputs. MATLAB returns the output once the execution of magicWithSend is complete.

ans = 3×3

 8     1     6
 3     5     7
 4     9     2

Use the poll function to collect data from the queue.

Define Helper Function

Define the helper function magicWithSend. The function creates a magic square, then sends the sum of the magic square to a DataQueue or PollableDataQueue object. After the sum is sent, the function returns the magic square.

function X = magicWithSend(q,n) X = magic(n); s = sum(X,'all'); send(q,s); end

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