Add celery task router

Add route_task function to route celery tasks to different queues.
If we can figure out what the module build is a task ran for by
checking the task arguments, then we route this task to a queue
named:

    "mbs-{}".format(module_build_id % num_workers)

"num_workers" has default value of 1, and can be changed in
backend_config.py. If module build id can't be figured out, task will
be routed to the default queue which is named "mbs-default".

While setting up the workers, the number of workers should match with
"num_workers" in config, and each worker will listen on two queues:

    1. mbs-default
    2. mbs-{number} # for example, the first worker listens on "mbs-0"

By this design, all tasks for a particular module build will be routed
to the same queue and run on the same worker serially.

module_build_service/config.py

@@ -670,6 +670,19 @@ class Config(object):
             "default": 30,
             "desc": "The timeout configuration for dnf operations, in seconds."
         },
+        "num_workers": {"type": int, "default": 1, "desc": "Number of Celery workers"},
+        "celery_task_always_eager": {
+            "type": bool,
+            "default": False,
+            "desc": "All Celery tasks will be executed locally by blocking until the task returns "
+                    "when this is True",
+        },
+        "celery_task_routes": {
+            "type": list,
+            "default": ["module_build_service.route.route_task"],
+            "desc": "A list of Celery routers. When deciding the final destination queue of a "
+                    "Celery task the routers are consulted in order",
+        },
         "celery_worker_prefetch_multiplier": {
             "type": int,
             "default": 1,

module_build_service/route.py

@@ -0,0 +1,69 @@
+# -*- coding: utf-8 -*-
+# SPDX-License-Identifier: MIT
+""" Define the router used to route Celery tasks to queues."""
+import inspect
+
+from module_build_service import conf, log, models
+from module_build_service.db_session import db_session
+from module_build_service.scheduler.handlers.greenwave import get_corresponding_module_build
+
+
+def route_task(name, args, kwargs, options, task=None, **kw):
+    """
+    Figure out module build id from task args and route task to queue
+    per the module build id.
+
+    Each celery worker will listens on two queues:
+        1. mbs-default
+        2. mbs-{number}  # where number is "module_build_id % conf.num_workers"
+    If a task is associated with a module build, route it to the queue
+    named "mbs-{number}", otherwise, route it to "mbs-default", this is to ensure
+    tasks for a module build can run on the same worker serially.
+    """
+    queue_name = "mbs-default"
+
+    module_build_id = None
+    num_workers = conf.num_workers
+
+    module, handler_name = name.rsplit(".", 1)
+    handler = getattr(__import__(module, fromlist=[handler_name]), handler_name)
+    # handlers can be decorated, inspect the original function
+    while getattr(handler, "__wrapped__", None):
+        handler = handler.__wrapped__
+    handler_args = inspect.getargspec(handler).args
+
+    def _get_handler_arg(name):
+        index = handler_args.index(name)
+        arg_value = kwargs.get(name, None)
+        if arg_value is None and len(args) > index:
+            arg_value = args[index]
+        return arg_value
+
+    if "module_build_id" in handler_args:
+        module_build_id = _get_handler_arg("module_build_id")
+
+    # if module_build_id is not found, we may be able to figure it out
+    # by checking other arguments
+    if module_build_id is None:
+        if "task_id" in handler_args:
+            task_id = _get_handler_arg("task_id")
+            component_build = models.ComponentBuild.from_component_event(db_session, task_id)
+            if component_build:
+                module_build_id = component_build.module_build.id
+        elif "tag_name" in handler_args:
+            tag_name = _get_handler_arg("tag_name")
+            module_build = models.ModuleBuild.get_by_tag(db_session, tag_name)
+            if module_build:
+                module_build_id = module_build.id
+        elif "subject_identifier" in handler_args:
+            module_build_nvr = _get_handler_arg("subject_identifier")
+            module_build = get_corresponding_module_build(module_build_nvr)
+            if module_build is not None:
+                module_build_id = module_build.id
+
+    if module_build_id is not None:
+        queue_name = "mbs-{}".format(module_build_id % num_workers)
+
+    taskinfo = {"name": name, "args": args, "kwargs": kwargs, "options": options, "kw": kw}
+    log.debug("Routing task '{}' to queue '{}'. Task info:\n{}".format(name, queue_name, taskinfo))
+    return {"queue": queue_name}

module_build_service/scheduler/events.py

@@ -66,22 +66,20 @@ class Scheduler(sched.scheduler):
 scheduler = Scheduler(time.time, delayfunc=lambda x: x)
 
 
-def mbs_event_handler():
+def mbs_event_handler(func):
     """
     A decorator for MBS event handlers. It implements common tasks which should otherwise
     be repeated in every MBS event handler, for example:
 
       - at the end of handler, call events.scheduler.run().
     """
-
-    def decorator(func):
-        @wraps(func)
-        def wrapper(*args, **kwargs):
-            try:
-                return func(*args, **kwargs)
-            finally:
-                scheduler.run()
-
-        return wrapper
-
-    return decorator
+    @wraps(func)
+    def wrapper(*args, **kwargs):
+        try:
+            return func(*args, **kwargs)
+        finally:
+            scheduler.run()
+    # save origin function as functools.wraps from python2 doesn't preserve the signature
+    if not hasattr(wrapper, "__wrapped__"):
+        wrapper.__wrapped__ = func
+    return wrapper

module_build_service/scheduler/handlers/components.py

@@ -17,7 +17,7 @@ logging.basicConfig(level=logging.DEBUG)
 
 
 @celery_app.task
-@events.mbs_event_handler()
+@events.mbs_event_handler
 def build_task_finalize(
         msg_id, build_id, task_id, build_new_state,
         build_name, build_version, build_release,

module_build_service/scheduler/handlers/greenwave.py

@@ -33,7 +33,7 @@ def get_corresponding_module_build(nvr):
 
 
 @celery_app.task
-@events.mbs_event_handler()
+@events.mbs_event_handler
 def decision_update(msg_id, decision_context, subject_identifier, policies_satisfied):
     """Move module build to ready or failed according to Greenwave result
 

module_build_service/scheduler/handlers/modules.py

@@ -41,7 +41,7 @@ def get_artifact_from_srpm(srpm_path):
 
 
 @celery_app.task
-@events.mbs_event_handler()
+@events.mbs_event_handler
 def failed(msg_id, module_build_id, module_build_state):
     """Called whenever a module enters the 'failed' state.
 
@@ -102,7 +102,7 @@ def failed(msg_id, module_build_id, module_build_state):
 
 
 @celery_app.task
-@events.mbs_event_handler()
+@events.mbs_event_handler
 def done(msg_id, module_build_id, module_build_state):
     """Called whenever a module enters the 'done' state.
 
@@ -141,7 +141,7 @@ def done(msg_id, module_build_id, module_build_state):
 
 
 @celery_app.task
-@events.mbs_event_handler()
+@events.mbs_event_handler
 def init(msg_id, module_build_id, module_build_state):
     """Called whenever a module enters the 'init' state.
 
@@ -317,7 +317,7 @@ def get_content_generator_build_koji_tag(module_deps):
 
 
 @celery_app.task
-@events.mbs_event_handler()
+@events.mbs_event_handler
 def wait(msg_id, module_build_id, module_build_state):
     """ Called whenever a module enters the 'wait' state.
 

module_build_service/scheduler/handlers/repos.py

@@ -14,7 +14,7 @@ logging.basicConfig(level=logging.DEBUG)
 
 
 @celery_app.task
-@events.mbs_event_handler()
+@events.mbs_event_handler
 def done(msg_id, tag_name):
     """Called whenever koji rebuilds a repo, any repo.
 

module_build_service/scheduler/handlers/tags.py

@@ -13,7 +13,7 @@ logging.basicConfig(level=logging.DEBUG)
 
 
 @celery_app.task
-@events.mbs_event_handler()
+@events.mbs_event_handler
 def tagged(msg_id, tag_name, build_name, build_nvr):
     """Called whenever koji tags a build to tag.