Add a system modeler to scheduler

So it can try to predict the effect its bindings will have.

plugin/pkg/scheduler/modeler.go

@@ -0,0 +1,155 @@
+/*
+Copyright 2015 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package scheduler
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/client/cache"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/labels"
+	algorithm "github.com/GoogleCloudPlatform/kubernetes/pkg/scheduler"
+
+	"github.com/golang/glog"
+)
+
+var (
+	_ = SystemModeler(&FakeModeler{})
+	_ = SystemModeler(&SimpleModeler{})
+)
+
+// ExtendedPodLister: SimpleModeler needs to be able to check for a pod's
+// existance in addition to listing the pods.
+type ExtendedPodLister interface {
+	algorithm.PodLister
+	Exists(pod *api.Pod) (bool, error)
+}
+
+// FakeModeler implements the SystemModeler interface.
+type FakeModeler struct {
+	AssumePodFunc func(pod *api.Pod)
+}
+
+// AssumePod calls the function variable if it is not nil.
+func (f *FakeModeler) AssumePod(pod *api.Pod) {
+	if f.AssumePodFunc != nil {
+		f.AssumePodFunc(pod)
+	}
+}
+
+// SimpleModeler implements the SystemModeler interface with a timed pod cache.
+type SimpleModeler struct {
+	queuedPods    ExtendedPodLister
+	scheduledPods ExtendedPodLister
+
+	// assumedPods holds the pods that we think we've scheduled, but that
+	// haven't yet shown up in the scheduledPods variable.
+	// TODO: periodically clear this.
+	assumedPods *cache.StoreToPodLister
+}
+
+// NewSimpleModeler returns a new SimpleModeler.
+//   queuedPods: a PodLister that will return pods that have not been scheduled yet.
+//   scheduledPods: a PodLister that will return pods that we know for sure have been scheduled.
+func NewSimpleModeler(queuedPods, scheduledPods ExtendedPodLister) *SimpleModeler {
+	return &SimpleModeler{
+		queuedPods:    queuedPods,
+		scheduledPods: scheduledPods,
+		assumedPods:   &cache.StoreToPodLister{cache.NewStore(cache.MetaNamespaceKeyFunc)},
+	}
+}
+
+func (s *SimpleModeler) AssumePod(pod *api.Pod) {
+	s.assumedPods.Add(pod)
+}
+
+// Extract names for readable logging.
+func podNames(pods []api.Pod) []string {
+	out := make([]string, len(pods))
+	for i := range pods {
+		out[i] = fmt.Sprintf("'%v/%v (%v)'", pods[i].Namespace, pods[i].Name, pods[i].UID)
+	}
+	return out
+}
+
+func (s *SimpleModeler) listPods(selector labels.Selector) (pods []api.Pod, err error) {
+	assumed, err := s.assumedPods.List(selector)
+	if err != nil {
+		return nil, err
+	}
+	// Since the assumed list will be short, just check every one.
+	// Goal here is to stop making assumptions about a pod once it shows
+	// up in one of these other lists.
+	// TODO: there's a possibility that a pod could get deleted at the
+	//       exact wrong time and linger in assumedPods forever. So we
+	//       need go through that periodically and check for deleted
+	//       pods.
+	for _, pod := range assumed {
+		qExist, err := s.queuedPods.Exists(&pod)
+		if err != nil {
+			return nil, err
+		}
+		if qExist {
+			s.assumedPods.Store.Delete(&pod)
+			continue
+		}
+		sExist, err := s.scheduledPods.Exists(&pod)
+		if err != nil {
+			return nil, err
+		}
+		if sExist {
+			s.assumedPods.Store.Delete(&pod)
+			continue
+		}
+	}
+
+	scheduled, err := s.scheduledPods.List(selector)
+	if err != nil {
+		return nil, err
+	}
+	// re-get in case we deleted any.
+	assumed, err = s.assumedPods.List(selector)
+	if err != nil {
+		return nil, err
+	}
+	if len(assumed) == 0 {
+		return scheduled, nil
+	}
+	glog.V(2).Infof(
+		"listing pods: [%v] assumed to exist in addition to %v known pods.",
+		strings.Join(podNames(assumed), ","),
+		len(scheduled),
+	)
+	return append(scheduled, assumed...), nil
+}
+
+// PodLister returns a PodLister that will list pods that we think we have scheduled in
+// addition to pods that we know have been scheduled.
+func (s *SimpleModeler) PodLister() algorithm.PodLister {
+	return simpleModelerPods{s}
+}
+
+// simpleModelerPods is an adaptor so that SimpleModeler can be a PodLister.
+type simpleModelerPods struct {
+	simpleModeler *SimpleModeler
+}
+
+// List returns pods known and assumed to exist.
+func (s simpleModelerPods) List(selector labels.Selector) (pods []api.Pod, err error) {
+	return s.simpleModeler.listPods(selector)
+}