eventor 1.0.7

eventor is a python programming facility to program event based sequence of activities

Overview

Eventor provides programmer with interface to create events, steps and associations of these artifacts with to create a flow.

It would be easier to show an example.

Simple Example

 1 import eventor as evr
 2 import logging
 3 
 4 logger=logging.getLogger(__name__)
 5 
 6 def prog(progname):
 7     logger.info("doing what %s is doing" % progname)
 8     return progname
 9 
10 ev=evr.Eventor(store=':memory:')
11 
12 ev1s=ev.add_event('run_step1')
13 ev2s=ev.add_event('run_step2')
14 ev3s=ev.add_event('run_step3')
15 
16 s1=ev.add_step('s1', func=prog, kwargs={'progname': 'prog1'},
17                triggers={evr.StepStatus.success: (ev2s,),})
18 s2=ev.add_step('s2', func=prog, kwargs={'progname': 'prog2'},
19                triggers={evr.StepStatus.success: (ev3s,), })
20 s3=ev.add_step('s3', func=prog, kwargs={'progname': 'prog3'},)
21 
22 ev.add_assoc(ev1s, s1)
23 ev.add_assoc(ev2s, s2)
24 ev.add_assoc(ev3s, s3)
25 
26 ev.trigger_event(ev1s, 1)
27 ev()

Example Output

The above example with provide the following log output.

[ 2016-11-30 10:07:48,572 ][ INFO ][ Eventor store file: :memory: ][ main.__init__ ]
[ 2016-11-30 10:07:48,612 ][ INFO ][ Running step s1[1] ][ main.task_wrapper ]
[ 2016-11-30 10:07:48,612 ][ INFO ][ Step completed s1[1], status: success, result 'prog1' ][ main.task_wrapper ]
[ 2016-11-30 10:07:50,649 ][ INFO ][ Running step s2[1] ][ main.task_wrapper ]
[ 2016-11-30 10:07:50,649 ][ INFO ][ Step completed s2[1], status: success, result 'prog2' ][ main.task_wrapper ]
[ 2016-11-30 10:07:52,688 ][ INFO ][ Running step s3[1] ][ main.task_wrapper ]
[ 2016-11-30 10:07:52,689 ][ INFO ][ Step completed s3[1], status: success, result 'prog3' ][ main.task_wrapper ]
[ 2016-11-30 10:07:53,700 ][ INFO ][ Processing finished ][ main.loop_session_start ]

Example Highlights

Eventor (line 10) defines an in-memory eventor object. Note that in-memory eventors are none recoverable.

add_event (e.g., line 12) adds an event named run_step1 to the respective eventor object.

add_step (e.g., line 16) adds step s1 which when triggered would run predefined function prog with key words parameters progname=’prog1’. Additionally, when step would end, if successful, it would trigger event evs2

add_assoc (e.g., line 22) links event evs1 and step s1.

trigger_event (line 26) marks event evs1; when triggers, event is associated with sequence. This would allow multiple invocation.

ev() (line 27) invoke eventor process that would looks for triggers and tasks to act upon. It ends when there is nothing to do.

Program Run File

One important artifact used in Eventor is program’s runner file. Runner file database (sqlite) will be created at execution, if not directed otherwise, at the location of the run (UNIX’s pwd). This file contains information on tasks and triggers that are used in the run and in recovery.

Eventor Interface

Eventor

Envtor Class Initiator

Eventor(name='', store='', run_mode=RunMode.restart, recovery_run=None, logging_level=logging.INFO, config={})

Args

name: string id for Eventor object initiated

store: path to file that would store runnable (sqlite) information; if ‘:memory:’ is used, in-memory temporary

storage will be created. If not provided, calling module path and name will be used with db extension instead of py

run_mode: can be either RunMode.restart (default) or RunMode.recover; in restart, new instance or the run

will be created. In recovery,

recovery_run: if RunMode.recover is used, recovery_run will indicate specific instance of previously recovery

run that would be executed.If not provided, latest run would be used.

config: keyword dictionary of default configurations. Available keywords and their default values:

Name	Default Value	Description
workdir	/tmp	place to create necessry artifacts (not in use)
logdir	/tmp	place to create debug and error log files
task_construct	mp.Process	method to use for execution of steps
max_concurrent	1	maximum concurrent processing, if value <1, no limit will be pose
stop_on_exception	True	if an exception occurs in a step, stop all processes. If True, new processes will not start. But running processes will be permitted to finish
sleep_between_loops	1	seconds to sleep between iteration of checking triggers and tasks

Envtor add_event method

add_event(name, expr=None)

Args

name: string unique id for event

expr: logical expression ‘sqlalchemy’ style to automatically raise this expresion.

syntax:

expr : (expr, expr, ...)
     | or_(expr, expr, ...)
     | event

• if expression is of the first style, logical and will apply.

• the second expression will apply logical or.

• the basic atom in expression is even which is the product of add_event.

Returns

Event object to use in other add_event expressions, add_assoc methods, or with add_step triggers.

Envtor add_step method

add_step(name, func, args=(), kwargs={}, triggers={}, recovery={}, config={})

Args

name: string unique id for step

func: callable object that would be call at time if step execution

args: tuple of values that will be passed to func at calling

kwargs: keywords arguments that will be pust to func at calling

triggers: mapping of step statuses to set of events to be triggered as in the following table:

status	description
StepState.ready	set when task is ready to run (triggered)
StepState.active	set when task is running
StepState.success	set when task is successful
StepState.failure	set when task fails
StepState.complete	stands for success or failure of task

recovery: mapping of state status to how step should be handled in recovery:

status	default	description
TaskStatus.ready	StepReplay.rerun	if in recovery and previous status is ready, rerun
TaskStatus.active	StepReplay.rerun	if in recovery and previous status is active, rerun
TaskStatus.failure	StepReplay.rerun	if in recovery and previous status is failure, rerun
TaskStatus.success	StepReplay.skip	if in recovery and previous status is success, skip

config: keywords mapping overrides for step configuration.

name	default	description
stop_on_exception	True	stop flow if step ends with Exception

Returns

Step object to use in add_assoc method.

Envtor add_assoc method

add_assoc(event, *assocs)

Args

event: event objects as provided by add_event.

assocs: list of associations objects. List is composed from either events (as returned by add_event) or steps (as returned by add_step)

Returns

N/A

Eventor trigger_event method

trigger_event(event, sequence=None)

Args

event: event objects as provided by add_event.

sequence: unique association of triggered event. Event can be triggered only once per sequence. All derivative triggers will carry the same sequence.

Returns

N/A

Recovery

When running in recovery, unless indicated otherwise, latest run (initial or recovery) would be used.

Note that when running a program with the intent to use its recovery capabilities, in-memory store cannot be use. Instead, physical storage must be used.

Here is an example for recovery program and run.

Recovery Example

 1 import eventor as evr
 2 import logging
 3 import math
 4 
 5 logger=logging.getLogger(__name__)
 6 
 7 logger.setLevel(logging.DEBUG)
 8 
 9 def square(x):
10     y=x*x
11     logger.info("Square of %s is %s" % (x, y))
12     return y
13 
14 def square_root(x):
15     y=math.sqrt(x)
16     logger.info("Square root of %s is %s" % (x, y))
17     return y
18 
19 def divide(x,y):
20     z=x/y
21     logger.info("dividing %s by %s is %s" % (x, y, z))
22     return z
23 
24 def build_flow(run_mode=evr.RunMode.restart, param=9):
25     ev=evr.Eventor(run_mode=run_mode, logging_level=logging.INFO)
26 
27     ev1s=ev.add_event('run_step1')
28     ev1d=ev.add_event('done_step1')
29     ev2s=ev.add_event('run_step2')
30     ev2d=ev.add_event('done_step2')
31     ev3s=ev.add_event('run_step3', expr=(ev1d, ev2d))
32 
33     s1=ev.add_step('s1', func=square, kwargs={'x': 3},
34                    triggers={evr.StepStatus.success: (ev1d, ev2s,)},)
35     s2=ev.add_step('s2', square_root, kwargs={'x': param}, triggers={evr.StepStatus.success: (ev2d,), },
36                    recovery={evr.StepStatus.failure: evr.StepReplay.rerun,
37                              evr.StepStatus.success: evr.StepReplay.skip})
38     s3=ev.add_step('s3', divide, kwargs={'x': 9, 'y': 3},)
39 
40     ev.add_assoc(ev1s, s1)
41     ev.add_assoc(ev2s, s2)
42     ev.add_assoc(ev3s, s3)
43     ev.trigger_event(ev1s, 3)
44     return ev
45 
46 # start regularly; it would fail in step 2
47 ev=build_eventor(param=-9)
48 ev()
49 
50 # rerun in recovery
51 ev=build_eventor(evr.RunMode.recover, param=9)
52 ev()

Example Output

 1 [ 2016-12-07 08:37:53,541 ][ INFO ][ Eventor store file: /eventor/example/runly03.run.db ]
 2 [ 2016-12-07 08:37:53,586 ][ INFO ][ [ Step s1/3 ] Trying to run ]
 3 [ 2016-12-07 08:37:53,588 ][ INFO ][ Square of 3 is 9 ]
 4 [ 2016-12-07 08:37:53,588 ][ INFO ][ [ Step s1/3 ] Completed, status: TaskStatus.success ]
 5 [ 2016-12-07 08:37:55,644 ][ INFO ][ [ Step s2/3 ] Trying to run ]
 6 [ 2016-12-07 08:37:55,647 ][ INFO ][ [ Step s2/3 ] Completed, status: TaskStatus.failure ]
 7 [ 2016-12-07 08:37:56,663 ][ ERROR ][ Exception in run_action:
 8     <Task(id='2', step_id='s2', sequence='3', recovery='0', pid='8112', status='TaskStatus.failure', created='2016-12-07 14:37:55.625870', updated='2016-12-07 14:37:55.633819')> ]
 9 [ 2016-12-07 08:37:56,663 ][ ERROR ][ ValueError('math domain error',) ]
10 [ 2016-12-07 08:37:56,663 ][ ERROR ][ File "/sand/eventor/eventor/main.py", line 62, in task_wrapper
11             result=step(seq_path=task.sequence)
12 File "/sand/eventor/eventor/step.py", line 82, in __call__
13             result=func(*func_args, **func_kwargs)
14 File "/eventor/example/runly03.py", line 66, in square_root
15         y=math.sqrt(x) ]
16 [ 2016-12-07 08:37:56,663 ][ INFO ][ Stopping running processes ]
17 [ 2016-12-07 08:37:56,667 ][ INFO ][ Processing finished: False ]
18 [ 2016-12-07 08:37:56,670 ][ INFO ][ Eventor store file: /eventor/example/runly03.run.db ]
19 [ 2016-12-07 08:37:57,736 ][ INFO ][ [ Step s2/3 ] Trying to run ]
20 [ 2016-12-07 08:37:57,739 ][ INFO ][ Square root of 9 is 3.0 ]
21 [ 2016-12-07 08:37:57,739 ][ INFO ][ [ Step s2/3 ] Completed, status: TaskStatus.success ]
22 [ 2016-12-07 08:38:00,798 ][ INFO ][ [ Step s3/3 ] Trying to run ]
23 [ 2016-12-07 08:38:00,800 ][ INFO ][ dividing 9 by 3 is 3.0 ]
24 [ 2016-12-07 08:38:00,800 ][ INFO ][ [ Step s3/3 ] Completed, status: TaskStatus.success ]
25 [ 2016-12-07 08:38:01,824 ][ INFO ][ Processing finished: True ]

Example Highlights

The function build_flow (code line 24) build an eventor flow using three functions defined in advance. Since no specific store is provided in Eventor instantiation, a default runner store is assigned (code line 25). In this build, step s2 (lines 30-35) is being set with recovery directives.

The first build and run is done in lines 47-48. In this run, a parameter that would cause the second step to fail is being passed. As a result, flow fails. Output lines 1-17 is associated with the first run.

The second build and run is then initiated. In this run, parameter is set to a value that ould pass step s2 and run mode is set to recovery (code lines 51-52). Eventor skips successful steps and start executing from failed steps onwards. Output lines 18-25 reflects successful second run.

Additional Information

Eventor github project (https://github.com/Acrisel/eventor) has additional examples with more complicated flows.