client cli and usage example

usage/example_server.py

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+import asyncio
+import logging
+
+from asyncio_taskpool import TaskPool, UnixControlServer
+from asyncio_taskpool.constants import PACKAGE_NAME
+
+
+logging.getLogger().setLevel(logging.NOTSET)
+logging.getLogger(PACKAGE_NAME).addHandler(logging.StreamHandler())
+
+
+async def work(item: int) -> None:
+    """The non-blocking sleep simulates something like an I/O operation that can be done asynchronously."""
+    await asyncio.sleep(1)
+    print("worked on", item)
+
+
+async def worker(q: asyncio.Queue) -> None:
+    """Simulates doing asynchronous work that takes a little bit of time to finish."""
+    # We only want the worker to stop, when its task is cancelled; therefore we start an infinite loop.
+    while True:
+        # We want to block here, until we can get the next item from the queue.
+        item = await q.get()
+        # Since we want a nice cleanup upon cancellation, we put the "work" to be done in a `try:` block.
+        try:
+            await work(item)
+        except asyncio.CancelledError:
+            # If the task gets cancelled before our current "work" item is finished, we put it back into the queue
+            # because a worker must assume that some other worker can and will eventually finish the work on that item.
+            q.put_nowait(item)
+            # This takes us out of the loop. To enable cleanup we must re-raise the exception.
+            raise
+        finally:
+            # Since putting an item into the queue (even if it has just been taken out), increments the internal
+            # `._unfinished_tasks` counter in the queue, we must ensure that it is decremented before we end the
+            # iteration or leave the loop. Otherwise, the queue's `.join()` will block indefinitely.
+            q.task_done()
+
+
+async def main() -> None:
+    # First, we set up a queue of items that our workers can "work" on.
+    q = asyncio.Queue()
+    # We just put some integers into our queue, since all our workers actually do, is print an item and sleep for a bit.
+    for item in range(100):
+        q.put_nowait(item)
+    pool = TaskPool(worker, (q,))  # initializes the pool
+    pool.start(3)  # launches three worker tasks
+    control_server_task = await UnixControlServer(pool, path='/tmp/py_asyncio_taskpool.sock').serve_forever()
+    # We block until `.task_done()` has been called once by our workers for every item placed into the queue.
+    await q.join()
+    # Since we don't need any "work" done anymore, we can close our control server by cancelling the task.
+    control_server_task.cancel()
+    # Since our workers should now be stuck waiting for more items to pick from the queue, but no items are left,
+    # we can now safely cancel their tasks.
+    pool.stop_all()
+    # Finally we allow for all tasks to do do their cleanup, if they need to do any, upon being cancelled.
+    # We block until they all return or raise an exception, but since we are not interested in any of their exceptions,
+    # we just silently collect their exceptions along with their return values.
+    await pool.gather(return_exceptions=True)
+    await control_server_task
+
+
+if __name__ == '__main__':
+    asyncio.run(main())