poll - Retrieve data from PollableDataQueue - MATLAB (original) (raw)

Retrieve data from PollableDataQueue

Syntax

Description

[data](#mw%5F05dee558-ad5c-4689-904b-0fe9147da410) = poll([q](#mw%5Fdda4dbb3-95f2-451a-b43b-af3118672d3a)) retrieves one item of data from the PollableDataQueue object q. Send data from the background or your current MATLAB® session using send.

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

[data](#mw%5F05dee558-ad5c-4689-904b-0fe9147da410) = poll([q](#mw%5Fdda4dbb3-95f2-451a-b43b-af3118672d3a),[timeout](#mw%5F8fc9b947-4cc4-4422-8894-73c4c27d693e)) waits timeout seconds to retrieve an item of data from thePollableDataQueue object q.

example

[[data](#mw%5F05dee558-ad5c-4689-904b-0fe9147da410),[tf](#mw%5F84199d1c-f3dc-4347-8407-3040b686be7d)] = poll(___) tries to retrieve data from a queue and returns a flagtf. If poll returns data,tf is true. Otherwise, tf isfalse.

You can use this syntax with any of the input argument combinations in the previous syntaxes. For example, [data,tf] = poll(q,5) waits to retrieve data from the queue q for five seconds.

Examples

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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

Input Arguments

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Queue, specified as a PollableDataQueue object.

The destination behavior of the queue, set using the Destination argument of the parallel.pool.PollableDataQueue function, determines where you can poll for data:

Before R2025a: You must callpoll on the client session or background worker in which you created the pollable data queue.

If you close aPollableDataQueue using the close function, you can no longer send data to the queue but you can continue poll for data in the queue. (since R2025a)

Seconds to wait for, specified as a real numeric scalar.

Example: timeout = 5;

Example: timeout = single(3.14);

Output Arguments

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Data sent to the queue, specified as scalar, vector, matrix, or multidimensional array.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical | char | string | struct | table | cell | function_handle | categorical | datetime | duration | calendarDuration

Flag to specify if data has been returned, returned as true orfalse.

Extended Capabilities

Version History

Introduced in R2017a