Multithreading library in matlab

Hi,

My question is simple, is there a way to run threads in matlab like in cpp using <thread> or <pthread> standard library.

Thx in advance !

Answer 1

[Jan]

No. You can use the command parfor and spmd, but this does not match the C++ threads exactly.

[Walter Roberson]

Note: since R2020b it has been possible to configure parfor to use threads instead of separate processes. However, you cannot start new threads at will, and you cannot communicate between threads.

[Rashi Mehrotra]

Is it possible to use parfor/spmd for data recived on udp connection?Do u suggest to switch to C?

[Raymond Norris]

At the time of Walter's writing, he's right. With that said, in R2021b we've now released backgroundPool, which can execute on a separate thread if you don't have Parallel Computing Toolbox or up to 8 threads with Parallel Computing Toolbox.

[Walter Roberson]

Communicating to/from background threads is still weak. Background threads are invoked through the parfeval() mechanism, which involves passing in a function handle, and passing in a list of parameters.

Background evaluation does not read from the environment; you cannot access the base workspace, and globals are not copied into the background.

Notice that the global I set in one thread is not always available on the next run, but is sometimes. This is likely due to the pool generated here having 4 workers: if setting globals works inside an individual worker until the worker is destroyed, but the globals are not copied between workers, then you would expect this behaviour, that the change does not become visible until the worker ends up getting re-used (you cannot choose the worker.)

From past experience, the behaviour of globals tells me that it is quite likely that device objects are not being copied into the background space, and so need to be created in the background space.

To send back data from a background thread, maybe it would work to create a dataqueue and pass it into the thread as a parameter. But that would require the Parallel Computing Toolbox if it were going to work at all.

global AAA
AAA = 'this is a global';
BBB = 'this is a local in the base workspace'

BBB = 'this is a local in the base workspace'

P = backgroundPool

P = 
  BackgroundPool with properties:

    NumWorkers: 2

tests = {@testbackground1, @testbackground2, @testbackground3, @testbackground3, @testbackground3, @testbackground3, @testbackground3};

for K = 1 : length(tests)
    F = parfeval(P, tests{K}, 1)
    try
        fetchOutputs(F)
    catch ME
        fprintf('well, test #%d did not work', K)
    end
end

F = 
 FevalFuture with properties: 

                   ID: 7
             Function: @testbackground1
       CreateDateTime: 13-Oct-2021 18:55:22
        StartDateTime: 13-Oct-2021 18:55:22
      RunningDuration: 0 days 0h 0m 0s
                State: finished (unread)
                Error: Unrecognized function or variable 'BBB'.
                       LiveEditorEvaluationHelperEeditorId>testbackground1 (line 19)

well, test #1 did not work

F = 
 FevalFuture with properties: 

                   ID: 8
             Function: @testbackground2
       CreateDateTime: 13-Oct-2021 18:55:23
        StartDateTime: 13-Oct-2021 18:55:23
      RunningDuration: 0 days 0h 0m 0s
                State: finished (unread)
                Error: Use of function evalin is not supported on a thread-based worker. Use alternatives supported on the background pool.
                       LiveEditorEvaluationHelperEeditorId>testbackground2 (line 23)

well, test #2 did not work

F = 
 FevalFuture with properties: 

                   ID: 9
             Function: @testbackground3
       CreateDateTime: 13-Oct-2021 18:55:23
        StartDateTime: 13-Oct-2021 18:55:23
      RunningDuration: 0 days 0h 0m 0s
                State: finished (read)
                Error: none

ans =

     []

F = 
 FevalFuture with properties: 

                   ID: 10
             Function: @testbackground3
       CreateDateTime: 13-Oct-2021 18:55:23
        StartDateTime: 13-Oct-2021 18:55:23
      RunningDuration: 0 days 0h 0m 0s
                State: finished (read)
                Error: none

ans =

     []

F = 
 FevalFuture with properties: 

                   ID: 11
             Function: @testbackground3
       CreateDateTime: 13-Oct-2021 18:55:23
        StartDateTime: 13-Oct-2021 18:55:23
      RunningDuration: 0 days 0h 0m 0s
                State: finished (read)
                Error: none

ans = 'new value set in background'

F = 
 FevalFuture with properties: 

                   ID: 12
             Function: @testbackground3
       CreateDateTime: 13-Oct-2021 18:55:23
        StartDateTime: 13-Oct-2021 18:55:23
      RunningDuration: 0 days 0h 0m 0s
                State: finished (read)
                Error: none

ans = 'new value set in background'

F = 
 FevalFuture with properties: 

                   ID: 13
             Function: @testbackground3
       CreateDateTime: 13-Oct-2021 18:55:23
        StartDateTime: 13-Oct-2021 18:55:23
      RunningDuration: 0 days 0h 0m 0s
                State: finished (read)
                Error: none

ans = 'new value set in background'

delete(P)

function out = testbackground1
   out = BBB;    %refering to base workspace
end

function out = testbackground2
   out = evalin('base', 'BBB');    %refering to base workspace explicitly
end

function out = testbackground3
   global AAA;
   out = AAA;   %refering to explicit global
   AAA = 'new value set in background'
end