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Aioevt

Simplified Asyncio-Friendly Event Management

Problem

Asyncio offers a lot of utilities that provide thread-safe execution of coroutines and synchronous functions. However, there isn't any one "unified" way of emitting/catching events accross threads, and synchronization primitives are not themselves thread-safe. This can lead to unexpected behavior when trying to synchronize multiple event loops on multiple threads.

Solution

aioevt - After creating the manager, you can emit or await 'global' events in a thread-safe way. Callbacks can registered from any thread and target any event loop. This allows you to very easily share objects and quickly emit information without fussing with thread safety.

Documentation

Evt and EvtData

The core objects used throughout aioevt are the Evt and EvtData dataclassess.

  • Evt represents an event itself and is comprised of a name (identifier), func (callback), loop (for execution), and recurring (automatic re-scheduling)
  • EvtData consists only of args and kwargs which are splatted into callbacks as needed

Create a manager

Create an aioevt manager which uses the default event loop.

mgr = aioevt.Manager()

Register an event

Register a global event to be triggered from a provided event loop when a named event is emitted. This can be done in two ways: both through the mgr.register method, or the mgr.on decorator. An event can have multiple callbacks, and each callback will be invoked with the same parameters on each emit. Note: The return value of the event callback is not retrievable. If you'd like to handle a value from inside a callback, simply emit a different event and wait for it in the desired location.

mgr.register(
    name="MyEvent",         # Name by which the event will be referenced
    func=my_func,           # Synchronous or Asynchronous function
    loop=my_event_loop,     # Provide a target loop in which to execute the function, Default: None (get running)
    recurring=True,         # Determines if the event should be re-registered after the first emit, Default: True
)

and

@mgr.on(name="Add", loop=my_event_loop, recurring=True)
def my_callback(num1, num2, num3, num4):
    # e.g. run hard calculations within a ProcessPoolExecutor
    total = num1 + num2 + num3 + num4
    mgr.emit("Calculated", args=(total,))

mgr.emit_after(0.1, "Add", args=(1, 2, 3, 4))
data = await mgr.wait("Calculated")
assert data.args[0] == 10

Emitting an event

Emit a signal with arbitrary positional and/or keyword parameters. This can be done with mgr.emit or mgr.emit_after which is identical except that it accepts an additional delay argument as its first parameter.

mgr.emit(
    name="MyEvent",         # Name of the event to emit
    args=(1, 2, 3),         # Tuple of args used to emit
    kwargs={"num4": 4},     # Dict of kwargs used to emit     
)

Waiting for an event

Using mgr.wait, you can asynchronously wait until an event is fired. This is commonly used just to wait for a certain status, but will also return an EvtData object which contains the args and kwargs values that were passed into the call to mgr.emit

data = await mgr.wait(
    name="MyEvent",         # Name of the event to wait for
    timeout=None,           # Timeout in seconds, Default: None
)

print(data.args)            # mgr.emit(..., args=...)
print(data.kwargs)          # mgr.emit(..., kwargs=...)

Unregistering an event

Recurring events can be unregistered manually both by name and by function value. Note that unregistering by name is significantly faster and more efficient, so use that when possible.

mgr.unregister(name="MyEventName")
mgr.unregister(func=my_callback_func)

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