Processes

Table of contents

• Start
• Request stop
• Event callbacks
• Register

Start

Time consuming operations or measurements need to be decoupled into threads to keep the user interface responsive and usable. COMET provides class Process for convenient thread handling.

import comet

def run(process):
    pass # perform some task

process = comet.Process(target=run)
process.start()

Request stop

COMET processes can be stopped by calling method stop(). This will put the process in stop-requested mode. Use properties running or stopping to terminate the running process gracefully.

import comet

def run(process):
    while process.running:
        pass # perform some task

process = comet.Process(target=run)
process.start()
...
process.stop()
process.join() # wait for process to stop

Event callbacks

Class Process provides the following built in callbacks to provide communication between worker thread and main thread:

• started is called immediately after start()
• failed is called if an exception was thrown, providing the exception and traceback object.
• finished is called immediately after running process ended, also if an exception occurred.

def on_finished():
    ui.show_info(title="My Process", text="Process finished!")
def on_error(exc, tb):
    ui.show_exception(exc, tb)

def run(process):
    raise RuntimeError("Spam!")

process = comet.Process(
    target=run,
    started=lambda: print("started..."),
    failed=on_error,
    finished=on_finished
)
process.start()

Note: Do not reference the user interface from within a process method, use custom event callbacks to propagate information to the user interface (main thread).

def run(process):
    while process.running:
        process.emit('voltage', 24.00)
        process.emit('current', 0.05)

process = comet.Process(target=run)
process.voltage = update_voltage
process.current = update_current

Register

Register all processes so that they will be stopped properly on application exit.

process = comet.Process()
process.start()
app.processes.add("process", process)
# `stop()` and `join()` is called on application exit