Helper for running functions in a concurrent loop.
Project description
README
Package overview
concurrent_loop
provides helpers for running functions in a continuous
loop in a separate thread or process.
Installation
pip install concurrent_loop
Example usage
Code set up
The following code creates a class which increments a counter in a looped
process using the ProcessLoop
class (replace with ThreadLoop
instead to
run in a separate thread rather than process).
from concurrent_loop.loops import ProcessLoop class CounterIterator(object): """ Iterates a counter in a loop that runs in an independent process. """ counter = 0 # Value to be incremented concurrent_loop_runner = ProcessLoop(100) # Set up the controller that # will run any requested function every 100 ms in a separate process. def _increment(self, increment_val): """ Increment the internal counter once and print value. This will be run repeatedly in a process. Args: increment_val (int): The value to increment the internal counter by. """ self.counter += increment_val print(self.counter) def concurrent_start(self): """ Run the _increment() function in the process loop. """ # Increments the internal counter in steps of 2. Arg must be supplied # as a tuple. self.concurrent_loop_runner.start(self._increment, (2,)) def concurrent_stop(self): """ Stop the process loop. """ self.concurrent_loop_runner.stop()
Start up
Finally, in the main code:
iter = CounterIterator() iter.concurrent_start() sleep(1) iter.concurrent_stop()
Exception handling
When an exception is raised in the underlying concurrent loop, the concurrent
loop stops, but the main process thread has no automatic knowledge of it.
The user code can read any exceptions raised from the ThreadLoop. exception
or ProcessLoop.exception
property.
In the above example, we would read:
iter.concurrent_loop_runner.exception
Asynchronous communication with Queue()
Both multiprocessing.Queue
and queue.Queue
allow asynchronous
communications with the concurrent loop. However, to ensure correct
functioning of the queue, the following rules must be adhered to:
- The class that calls the
ThreadLoop
orProcessLoop
(which is theCounterIterator
class in above example) must create theQueue
instance as an instance attribute, and not as a class attribute. - The
Queue
instance must be passed into looped function (the_increment
function in above example) as a function parameter, and not called from the looped function as an attribute.
To extend the above example so that _increment
function sends the
counter value to a results queue on each loop, we do the following.
Import the queue module (for this example, we'll use the simpler
multiprocessing.Queue
):
from multiprocessing import Queue
Instantiate a results queue in CounterIterator.__init__
:
class CounterIterator(object): _results_q = None def __init__(self): self._results_q = Queue()
Modify the _increment
function to put the counter value into the results
queue:
def _increment(self, res_q, increment_val) self.counter += increment_val res_q.put_nowait(self._counter)
Pass the results queue from concurrent_start
method into the _increment
function.
def concurrent_start(self): self.concurrent_loop_runner.start(self._increment, (self._results_q, 2))
Define a counter getter that gets the counter value from the FIFO results queue:
@property def counter(self): return self._results_q.get()
In the main code, to print out the counter value from the first 10 loops:
iter = CounterIterator() iter.concurrent_start() for _ in range(10): print(iter.counter) iter.concurrent_stop()
Who do I talk to?
- The author: KCLee
- Email: lathe-rebuke.0c@icloud.com
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