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scheduler.go
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scheduler.go
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// Copyright 2014 CoreOS, Inc.
//
// 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 engine
import (
"fmt"
"sort"
"github.com/coreos/fleet/agent"
"github.com/coreos/fleet/job"
)
type decision struct {
machineID string
}
type Scheduler interface {
Decide(*clusterState, *job.Job) (*decision, error)
}
type leastLoadedScheduler struct{}
func (lls *leastLoadedScheduler) Decide(clust *clusterState, j *job.Job) (*decision, error) {
agents := lls.sortedAgents(clust)
if len(agents) == 0 {
return nil, fmt.Errorf("zero agents available")
}
var target *agent.AgentState
for _, as := range agents {
if able, _ := as.AbleToRun(j); !able {
continue
}
as := as
target = as
break
}
if target == nil {
return nil, fmt.Errorf("no agents able to run job")
}
dec := decision{
machineID: target.MState.ID,
}
return &dec, nil
}
// sortedAgents returns a list of AgentState objects sorted ascending
// by the number of scheduled units
func (lls *leastLoadedScheduler) sortedAgents(clust *clusterState) []*agent.AgentState {
agents := clust.agents()
sas := make(sortableAgentStates, 0)
for _, as := range agents {
sas = append(sas, as)
}
sort.Sort(sas)
return []*agent.AgentState(sas)
}
type sortableAgentStates []*agent.AgentState
func (sas sortableAgentStates) Len() int { return len(sas) }
func (sas sortableAgentStates) Swap(i, j int) { sas[i], sas[j] = sas[j], sas[i] }
func (sas sortableAgentStates) Less(i, j int) bool {
niUnits := len(sas[i].Units)
njUnits := len(sas[j].Units)
return niUnits < njUnits || (niUnits == njUnits && sas[i].MState.ID < sas[j].MState.ID)
}