AddMessage not working in worker threads

[PlinioSantos]

I developed a script for ArcGIS Pro which performs 4 heavy downloads. To speed-up the process, I delegated the download process to 4 worker threads and wait for them complete in order to continue the geoprocess operations. During the download process, I use the arcpy.AddMessage() function to give some feedback.

Everything works as expected when I execute de code as a python standalone script, including the feedback messages. However some messeges did not show when running the script in ArcGIS Pro.

I suspect that the worker threads are writing the messages in somewhere else. To test my thoughs, I wrote the following script:

import concurrent.futures
import threading
import arcpy


def add_message_wrapper(message):
    arcpy.AddMessage('Thread {0} says: {1}'.format(threading.current_thread().getName(), message))


if __name__ == '__main__':
    add_message_wrapper('Hello addMessage')
    with concurrent.futures.ThreadPoolExecutor() as executor:
        futures = [executor.submit(add_message_wrapper,
                   'Hello addMessage from a worker thread') for i in range(6)]
        for future in concurrent.futures.as_completed(futures):
            pass
        add_message_wrapper('Back to main...')

The output as a standalone python script:

Thread MainThread says: Hello addMessage
Thread ThreadPoolExecutor-0_0 says: Hello addMessage from a worker thread
Thread ThreadPoolExecutor-0_0 says: Hello addMessage from a worker thread
Thread ThreadPoolExecutor-0_0 says: Hello addMessage from a worker thread
Thread ThreadPoolExecutor-0_1 says: Hello addMessage from a worker thread
Thread ThreadPoolExecutor-0_0 says: Hello addMessage from a worker thread
Thread ThreadPoolExecutor-0_2 says: Hello addMessage from a worker thread
Thread MainThread says: Back to main...

The  output as a script in ArcGIS Pro:

Messages
Start Time: sexta-feira, 1 de fevereiro de 2019 11:49:40
Running script testAddMessage...
Thread Dummy-1 says: Hello addMessage
Thread Dummy-1 says: Back to main...
Completed script testAddMessage...
Succeeded at sexta-feira, 1 de fevereiro de 2019 11:49:45 (Elapsed Time: 4,80 seconds)

So, how can I get the messages from worker threads sent to ArcGIS Pro output?

[DanPatterson_Retired]

probably just printing... build your message string and 'tweet' it

def tweet(msg):
    """Print a message for both arcpy and python.

    msg - a text message
    """
    m = "\n{}\n".format(msg)
    arcpy.AddMessage(m)
    print(m)‍‍‍‍‍‍‍‍

[PlinioSantos]

Dan, your solution duplicate the messages in python console (stand alone python script) and yet did not makes ArcGIS Pro output to show messages sent by a worker thread.

[DanPatterson_Retired]

wouldn't your worker scripts would need to return the messages to the main script then? or are your workers isolated once they are called?

[PlinioSantos]

All code are in the same python module, i.e., same script, just as the snippet in the main post. The concurrent.futures module starts worker threads to execute a funcion (heavy network operations in my real case) and the concurrent.futures.as_completed yelds the results as soon as the worker thread execution ends. My problem is that only messages sent from the starter thread are visible on ArcGIS Pro interface.