Class that enables sending and polling for data between client and workers
PollableDataQueue enables sending and polling for data or
messages between workers and client in a parallel pool while a computation is being
carried out. You can get intermediate values and progress of the computation.
To send data from a parallel pool worker back to the client, first construct a
PollableDataQueue in the client. Pass this
PollableDataQueue into a
other parallel language construct, such as
parfeval. From the
send to send data back to the client. At the
poll to retrieve the result of a message or data sent
from a worker.
You can call
send from the process that calls the
constructor, if required.
You can construct the queue on the workers and send it back to the client
to enable communication in the reverse direction. However, you cannot send a
queue from one worker to another. Use
Unlike all other handle objects,
instances do remain connected when they are sent to workers.
The constructor for a
PollableDataQueue takes no arguments and
returns an object that can be used to send and poll for messages (or data) from
different workers. You call the constructor only in the process where you want to
receive the data. In the usual workflow, the workers should not be calling the
constructor, but should be handed an existing
QueueLength— Number of items currently held on the queue
Read-only property that indicates how many items of data are waiting to be removed from the queue.
pollableQ = parallel.pool.PollableDataQueue; % No messages in queue because nothing has been sent yet. pollableQ.QueueLength
ans = 0
pollableQ.send('A message') % Now QueueLength = 1 because one message is sent and not yet polled. pollableQ.QueueLength
ans = 1
msg = pollableQ.poll(); disp(msg)
pollableQ.QueueLength % Now QueueLength = 0 because there are no more pending messages.
ans = 0
A parallel.pool.PollableDataQueue object has the following methods.
|poll||Retrieve data sent from a worker|
|send||Send data from worker to client using a data queue|
Handle. To learn how handle classes affect copy operations, see Copying Objects (MATLAB).
parfor-loop, and Poll for the Result
p = parallel.pool.PollableDataQueue;
parfor-loop, and send a message, such as
data with the value 1.
parfor i = 1 send(p, i); end
Poll for the result.
For more details on polling for data using a