# MATLAB PollableDataQueue get last value

24 views (last 30 days)
dleal on 28 Dec 2021
Edited: Walter Roberson on 3 Jan 2022
Is it possible to make the a MATLAB PollableDataQueue last-in-first-out (LIFO) instead of first-in-first-out (FIFO)? Alternatively, is there a way to get the last entry in a queue instead of the first one?
See for example, the following code that illustrates the current behavior of PollableDataQueue:
%parpool;
q = parallel.pool.PollableDataQueue;
f = parfeval(@test,1,q);
for jj = 1:4
poll(q)
pause(0.25)
end
fetchOutputs(f)
function x0 = test(q)
x0 = [];
for jj = 1:20
x0 = [x0, rand(1)];
send(q, x0);
pause(0.01);
end
end
ans =
[]
ans =
0.7918
ans =
0.7918 0.1528
ans =
0.7918 0.1528 0.0854
ans =
Columns 1 through 12
0.7918 0.1528 0.0854 0.9955 0.3557 0.1679 0.6713 0.5398 0.6599 0.9344 0.7200 0.4450
Columns 13 through 20
0.6622 0.4427 0.9791 0.5114 0.0200 0.6054 0.0479 0.3470
Calling "poll(q)" returns the values added to x0, one by one, in the order in which they are added to the queue (FIFO). Instead, I would like to retrieve the last value in the queue, at the moment in which the moment in which poll(q) is called.
For example, since the code below waits 0.25 seconds between successive calls to "poll(q)", and since values are added to x0 every 0.01 seconds, I would suspect that by the second time "poll(q)" is called, the 25th value of x0 should be already recorded. Yet, the second time I call "poll(q)" I only get the first entry (FIFO instead of LIFO).

Raymond Norris on 2 Jan 2022
How about prepending the value to the poll?
x0 = [rand(1), x0];
dleal on 3 Jan 2022
Simple and works! For reference, i will also link an answer i got on stackoverflow:

R2021b

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