spmdProbe

Determine whether data is available to current worker in spmd block

Since R2022b

Syntax

tf = spmdProbe

tf = spmdProbe(source)

tf = spmdProbe('any')

tf = spmdProbe('any',tag)

tf = spmdProbe(source,tag)

[tf,sourceOut,tagOut] = spmdProbe(___)

Description

tf = spmdProbe tests whether data is available to the current worker in an spmd block or communicating job. If it is 1, the worker can receive the data using spmdReceive.

When you offload computations using parfor and parfeval, only one worker at a time runs each computation. These workers are independent and do not communicate with each other. If you apply spmdProbe to these workers, the function has no effect.

If the data is available, spmdProbe returns a logical 1 (true). Otherwise, spmdProbe returns a logical 0 (false).

To use spmdProbe, the number of workers running the current spmd block must be greater than 1.

tf = spmdProbe(source) tests whether data is available for the current worker to receive from the worker whose index is equal to source.

tf = spmdProbe('any') tests whether the sent data is available for the current worker to receive from any worker.

tf = spmdProbe('any',tag) tests whether data sent with the tag tag is available for the current worker to receive from any worker.

tf = spmdProbe(source,tag) tests whether data sent with the tag tag is available for the current worker to receive from the worker whose index is equal to source.

[tf,sourceOut,tagOut] = spmdProbe(___) tests whether data is available for the current worker to receive, returns the index of the worker that is sending data as sourceOut, and returns the tag of available data as tagOut. If multiple items of data are available, spmdProbe returns the index and tag of the first matching message.

Examples

Determine Whether Data Has Been Sent to Worker in spmd Block

This example shows how to determine whether data is available for workers in an spmd block or communicating job to receive.

Create a parallel pool with four workers.

parpool(4);

When you execute an spmd block after creating a parallel pool, by default all available workers in the pool run the code inside the spmd block.

Create an spmd block. On the worker whose index is equal to 1, create an array. Use spmdSend to send the array to the worker whose index is equal to 2.

Use spmdBarrier to synchronise the workers after the worker whose index is equal to 1 sends the data. Then, use spmdProbe to test whether the data is available for each worker to receive. Use spmdReceive to collect the available data.

spmd
    switch spmdIndex
        case 1
            A = magic(3);
            spmdSend(A,2);
    end
    
    spmdBarrier;

    tf = spmdProbe
    
    if tf
        spmdReceive;
    end
end

Worker 1: 
  
  tf =
  
    logical
  
     0
  
Worker 2: 
  
  tf =
  
    logical
  
     1
  
Worker 3: 
  
  tf =
  
    logical
  
     0
  
Worker 4: 
  
  tf =
  
    logical
  
     0
  

Input Arguments

source — Index of source worker

positive integer | 'any'

Index of the source worker, specified as a positive integer or 'any'. The value of this input must be less than or equal to the number of workers running the current spmd block or communicating job.

When you specify this input as a positive integer, spmdProbe returns a logical 1 (true) if data is available for the current worker to receive from the worker whose index is equal to source.

When you specify this input as 'any', spmdProbe returns a logical 1 (true) if the data is available for the current worker to receive from any worker.

When you do not specify this input, spmdProbe returns a logical 1 (true) if the data is available for the current worker to receive from any worker.

Example: 1

tag — Message tag

nonnegative integer

Message tag, specified as a nonnegative integer. When you specify this input, spmdProbe returns a logical 1 (true) if the data sent using spmdSend with the tag equal to tag is available for the current worker to receive.

Example: 314159

Output Arguments

sourceOut — Index of worker sending data

positive integer | empty array

Index of the worker sending data that the current worker is yet to receive, returned as a positive integer or an empty array. The value is equal to index of the worker that sent data.

If no data is available to be received, sourceOut is [].

tagOut — Message tag

nonnegative integer | empty array

Message tag of the data that the current worker has not yet received, returned as a nonnegative integer or an empty array. If no data is available to be received, tagOut is [].

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 R2022b