Pyeventbus: a publish/subscribe event bus

Last update: Apr 21, 2022

Overview

pyeventbus

pyeventbus is a publish/subscribe event bus for Python 2.7.

simplifies the communication between python classes
decouples event senders and receivers
performs well threads, greenlets, queues and concurrent processes
avoids complex and error-prone dependencies and life cycle issues
makes code simpler
has advanced features like delivery threads, workers and spawning different processes, etc.
is tiny (3KB archive)

pyeventbus in 3 steps:

Define events:

class MessageEvent:
    # Additional fields and methods if needed
    def __init__(self):
        pass

Prepare subscribers: Declare and annotate your subscribing method, optionally specify a thread mode:

from pyeventbus import *

@subscribe(onEvent=MessageEvent)
def func(self, event):
    # Do something
    pass

from pyeventbus import *

class MyClass:
    def __init__(self):
        pass

    def register(self, myclass):
        PyBus.Instance().register(myclass, self.__class__.__name__)

# then during initilization

myclass = MyClass()
myclass.register(myclass)

Post events:

from pyeventbus import *

class MyClass:
    def __init__(self):
        pass

    def register(self, myclass):
        PyBus.Instance().register(myclass, self.__class__.__name__)

    def postingAnEvent(self):
        PyBus.Instance().post(MessageEvent())

 myclass = MyClass()
 myclass.register(myclass)
 myclass.postingAnEvent()

Modes: pyeventbus can run the subscribing methods in 5 different modes

POSTING:

Runs the method in the same thread as posted. For example, if an event is posted from main thread, the subscribing method also runs in the main thread. If an event is posted in a seperate thread, the subscribing method runs in the same seperate method

This is the default mode, if no mode has been provided::

@subscribe(threadMode = Mode.POSTING, onEvent=MessageEvent)
def func(self, event):
    # Do something
    pass

PARALLEL:

Runs the method in a seperate python thread::

@subscribe(threadMode = Mode.PARALLEL, onEvent=MessageEvent)
def func(self, event):
    # Do something
    pass

GREENLET:

Runs the method in a greenlet using gevent library::

@subscribe(threadMode = Mode.GREENLET, onEvent=MessageEvent)
def func(self, event):
    # Do something
    pass

BACKGROUND:

Adds the subscribing methods to a queue which is executed by workers::

@subscribe(threadMode = Mode.BACKGROUND, onEvent=MessageEvent)
def func(self, event):
    # Do something
    pass

CONCURRENT:

Runs the method in a seperate python process::

@subscribe(threadMode = Mode.CONCURRENT, onEvent=MessageEvent)
def func(self, event):
    # Do something
    pass

Adding pyeventbus to your project:

pip install pyeventbus

Example:

git clone https://github.com/n89nanda/pyeventbus.git

cd pyeventbus

virtualenv venv

source venv/bin/activate

pip install pyeventbus

python example.py

Benchmarks and Performance:

Refer /pyeventbus/tests/benchmarks.txt for performance benchmarks on CPU, I/O and networks heavy tasks.

Run /pyeventbus/tests/test.sh to generate the same benchmarks.

Performance comparison between all the modes with Python and Cython

Inspiration

Inspired by Eventbus from greenrobot: https://github.com/greenrobot/EventBus

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Comments

Same method name for multiple subscribers bug

Please see the code below. To summarize:

Define one event
Define two subscriber listening for the event above. Each subscriber has a listener method with the name on_event
Each of the subscriber classes above defines an instance field, but with unique name (self.something in the first class, self.something2 in the second class)
Define another class that posts an event

Run this scenario and get the error below:

Exception in thread thread-on_event:
Traceback (most recent call last):
  File "C:\Anaconda2\envs\python\lib\threading.py", line 801, in __bootstrap_inner
    self.run()
  File "C:\Anaconda2\envs\python\lib\site-packages\pyeventbus\pyeventbus.py", line 112, in run
    self.method(self.subscriber, self.event)
  File "C:/FractureID/projects/python/ui/spectraqc/PyEventBusBug.py", line 16, in on_event
    print (self.something)
AttributeError: Subscriber2 instance has no attribute 'something'

Exception in thread thread-on_event:
Traceback (most recent call last):
  File "C:\Anaconda2\envs\python\lib\threading.py", line 801, in __bootstrap_inner
    self.run()
  File "C:\Anaconda2\envs\python\lib\site-packages\pyeventbus\pyeventbus.py", line 112, in run
    self.method(self.subscriber, self.event)
  File "C:/FractureID/projects/python/ui/spectraqc/PyEventBusBug.py", line 26, in on_event
    print (self.something_else)
AttributeError: Subscriber1 instance has no attribute 'something_else'

It complains about the variable in class two not having the attribute in the first class and the other way around.

If I change on of the on_event to something else like on_event2 then the issue is gone.

from pyeventbus import *


class SomeEvent:
    def __init__(self):
        pass


class Subscriber1:
    def __init__(self):
        self.something = 'First subscriber'
        PyBus.Instance().register(self, self.__class__.__name__)

    @subscribe(threadMode=Mode.PARALLEL, onEvent=SomeEvent)
    def on_event(self, event):
        print (self.something)


class Subscriber2:
    def __init__(self):
        self.something_else = 'Second subscriber'
        PyBus.Instance().register(self, self.__class__.__name__)

    @subscribe(threadMode=Mode.PARALLEL, onEvent=SomeEvent)
    def on_event(self, event):
        print (self.something_else)


class PyEventBusBug:

    def __init__(self):
        Subscriber1()
        Subscriber2()
        PyBus.Instance().post(SomeEvent())


if __name__ == "__main__":
    PyEventBusBug()

bug

opened by ddanny 0

Doesn't even start on Windows because 2000 threads is apparently too much

  File "C:\Python27\lib\site-packages\pyeventbus\pyeventbus.py", line 116, in subscribe
    bus = PyBus.Instance()
  File "C:\Python27\lib\site-packages\pyeventbus\Singleton.py", line 30, in Instance
    self._instance = self._decorated()
  File "C:\Python27\lib\site-packages\pyeventbus\pyeventbus.py", line 24, in __init__
    for worker in [lambda: self.startWorkers() for i in range(self.num_threads)]: worker()
  File "C:\Python27\lib\site-packages\pyeventbus\pyeventbus.py", line 24, in <lambda>
    for worker in [lambda: self.startWorkers() for i in range(self.num_threads)]: worker()
  File "C:\Python27\lib\site-packages\pyeventbus\pyeventbus.py", line 30, in startWorkers
    worker.start()
  File "C:\Python27\lib\threading.py", line 736, in start
    _start_new_thread(self.__bootstrap, ())
thread.error: can't start new thread

See also: https://stackoverflow.com/a/1835043/2583080

bug

opened by PawelTroka 4

Releases(0.2)

0.2(Feb 2, 2018)

added performance benchmarks and tests
Source code(tar.gz)
Source code(zip)
0.1(Feb 2, 2018)

first stable release
Source code(tar.gz)
Source code(zip)

Owner

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