Make db_session singleton

Please note that this patch does not change the use of database session
in MBS. So, in the frontend, the database session is still managed by
Flask-SQLAlchemy, that is the db.session. And the backend, running event
handlers, has its own database session created from SQLAclehmy session
API directly.

This patch aims to reduce the number of scoped_session created when call
original function make_db_session. For technical detailed information,
please refer to SQLAlchemy documentation Contextual/Thread-local
Sessions.

As a result, a global scoped_session is accessible from the
code running inside backend, both the event handlers and functions
called from handlers. The library code shared by frontend and backend,
like resolvers, has no change.

Similarly, db.session is only used to recreate database for every test.

Signed-off-by: Chenxiong Qi <cqi@redhat.com>

module_build_service/builder/KojiModuleBuilder.py

@@ -25,6 +25,7 @@ import module_build_service.scm
 import module_build_service.utils
 from module_build_service.builder.utils import execute_cmd
 from module_build_service.builder.koji_backports import ClientSession as KojiClientSession
+from module_build_service.db_session import db_session
 from module_build_service.errors import ProgrammingError
 
 from module_build_service.builder.base import GenericBuilder
@@ -159,7 +160,7 @@ class KojiModuleBuilder(GenericBuilder):
         log.debug("Using koji_config: %s" % config.koji_config)
 
         self.koji_session = self.get_session(config)
-        self.arches = [arch.name for arch in self.module.arches]
+        self.arches = sorted(arch.name for arch in self.module.arches)
 
         # Allow KojiModuleBuilder to be initialized if no arches are set but the module is in
         # a failed set. This will allow the clean up of old module builds.
@@ -228,63 +229,61 @@ class KojiModuleBuilder(GenericBuilder):
         """
         # filtered_rpms will contain the NVRs of non-reusable component's RPMs
         filtered_rpms = list(set(filtered_rpms_of_dep))
-        with models.make_db_session(conf) as db_session:
-            # Get a module build that can be reused, which will likely be the
-            # build dep that is used since it relies on itself
-            reusable_module = get_reusable_module(db_session, module_build)
-            if not reusable_module:
-                return filtered_rpms
-            koji_session = KojiModuleBuilder.get_session(conf, login=False)
-            # Get all the RPMs and builds of the reusable module in Koji
-            rpms, builds = koji_session.listTaggedRPMS(reusable_module.koji_tag, latest=True)
-            # Convert the list to a dict where each key is the build_id
-            builds = {build["build_id"]: build for build in builds}
-            # Create a mapping of package (SRPM) to the RPMs in NVR format
-            package_to_rpms = {}
-            for rpm in rpms:
-                package = builds[rpm["build_id"]]["name"]
-                package_to_rpms.setdefault(package, []).append(kobo.rpmlib.make_nvr(rpm))
+        # Get a module build that can be reused, which will likely be the
+        # build dep that is used since it relies on itself
+        reusable_module = get_reusable_module(module_build)
+        if not reusable_module:
+            return filtered_rpms
+        koji_session = KojiModuleBuilder.get_session(conf, login=False)
+        # Get all the RPMs and builds of the reusable module in Koji
+        rpms, builds = koji_session.listTaggedRPMS(reusable_module.koji_tag, latest=True)
+        # Convert the list to a dict where each key is the build_id
+        builds = {build["build_id"]: build for build in builds}
+        # Create a mapping of package (SRPM) to the RPMs in NVR format
+        package_to_rpms = {}
+        for rpm in rpms:
+            package = builds[rpm["build_id"]]["name"]
+            package_to_rpms.setdefault(package, []).append(kobo.rpmlib.make_nvr(rpm))
 
-            components_in_module = [c.package for c in module_build.component_builds]
-            reusable_components = get_reusable_components(
-                db_session,
-                module_build,
-                components_in_module,
-                previous_module_build=reusable_module,
-            )
-            # Loop through all the reusable components to find if any of their RPMs are
-            # being filtered
-            for reusable_component in reusable_components:
-                # reusable_component will be None if the component can't be reused
-                if not reusable_component:
-                    continue
-                # We must get the component name from the NVR and not from
-                # reusable_component.package because macros such as those used
-                # by SCLs can change the name of the underlying build
-                component_name = kobo.rpmlib.parse_nvr(reusable_component.nvr)["name"]
+        components_in_module = [c.package for c in module_build.component_builds]
+        reusable_components = get_reusable_components(
+            module_build,
+            components_in_module,
+            previous_module_build=reusable_module,
+        )
+        # Loop through all the reusable components to find if any of their RPMs are
+        # being filtered
+        for reusable_component in reusable_components:
+            # reusable_component will be None if the component can't be reused
+            if not reusable_component:
+                continue
+            # We must get the component name from the NVR and not from
+            # reusable_component.package because macros such as those used
+            # by SCLs can change the name of the underlying build
+            component_name = kobo.rpmlib.parse_nvr(reusable_component.nvr)["name"]
 
-                if component_name not in package_to_rpms:
-                    continue
+            if component_name not in package_to_rpms:
+                continue
 
-                # Loop through the RPMs associated with the reusable component
-                for nvr in package_to_rpms[component_name]:
-                    parsed_nvr = kobo.rpmlib.parse_nvr(nvr)
+            # Loop through the RPMs associated with the reusable component
+            for nvr in package_to_rpms[component_name]:
+                parsed_nvr = kobo.rpmlib.parse_nvr(nvr)
+                # Don't compare with the epoch
+                parsed_nvr["epoch"] = None
+                # Loop through all the filtered RPMs to find a match with the reusable
+                # component's RPMs.
+                for nvr2 in list(filtered_rpms):
+                    parsed_nvr2 = kobo.rpmlib.parse_nvr(nvr2)
                     # Don't compare with the epoch
-                    parsed_nvr["epoch"] = None
-                    # Loop through all the filtered RPMs to find a match with the reusable
-                    # component's RPMs.
-                    for nvr2 in list(filtered_rpms):
-                        parsed_nvr2 = kobo.rpmlib.parse_nvr(nvr2)
-                        # Don't compare with the epoch
-                        parsed_nvr2["epoch"] = None
-                        # Only remove the filter if we are going to reuse a component with
-                        # the same exact NVR
-                        if parsed_nvr == parsed_nvr2:
-                            filtered_rpms.remove(nvr2)
-                            # Since filtered_rpms was cast to a set and then back
-                            # to a list above, we know there won't be duplicate RPMS,
-                            # so we can just break here.
-                            break
+                    parsed_nvr2["epoch"] = None
+                    # Only remove the filter if we are going to reuse a component with
+                    # the same exact NVR
+                    if parsed_nvr == parsed_nvr2:
+                        filtered_rpms.remove(nvr2)
+                        # Since filtered_rpms was cast to a set and then back
+                        # to a list above, we know there won't be duplicate RPMS,
+                        # so we can just break here.
+                        break
         return filtered_rpms
 
     @staticmethod
@@ -1280,18 +1279,17 @@ class KojiModuleBuilder(GenericBuilder):
         :param Modulemd mmd: Modulemd to get the built RPMs from.
         :return: list of NVRs
         """
-        with models.make_db_session(conf) as db_session:
-            build = models.ModuleBuild.get_build_from_nsvc(
-                db_session,
-                mmd.get_module_name(),
-                mmd.get_stream_name(),
-                mmd.get_version(),
-                mmd.get_context()
-            )
-            koji_session = KojiModuleBuilder.get_session(conf, login=False)
-            rpms = koji_session.listTaggedRPMS(build.koji_tag, latest=True)[0]
-            nvrs = set(kobo.rpmlib.make_nvr(rpm, force_epoch=True) for rpm in rpms)
-            return list(nvrs)
+        build = models.ModuleBuild.get_build_from_nsvc(
+            db_session,
+            mmd.get_module_name(),
+            mmd.get_stream_name(),
+            mmd.get_version(),
+            mmd.get_context()
+        )
+        koji_session = KojiModuleBuilder.get_session(conf, login=False)
+        rpms = koji_session.listTaggedRPMS(build.koji_tag, latest=True)[0]
+        nvrs = set(kobo.rpmlib.make_nvr(rpm, force_epoch=True) for rpm in rpms)
+        return list(nvrs)
 
     def finalize(self, succeeded=True):
         # Only import to koji CG if the module is "build" and not scratch.