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/*
*
* Copyright 2019 gRPC authors.
*
* 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 wrr
import (
"container/heap"
"sync"
)
// edfWrr is a struct for EDF weighted round robin implementation.
type edfWrr struct {
lock sync.Mutex
items edfPriorityQueue
currentOrderOffset uint64
currentTime float64
}
// NewEDF creates Earliest Deadline First (EDF)
// (https://en.wikipedia.org/wiki/Earliest_deadline_first_scheduling) implementation for weighted round robin.
// Each pick from the schedule has the earliest deadline entry selected. Entries have deadlines set
// at current time + 1 / weight, providing weighted round robin behavior with O(log n) pick time.
func NewEDF() WRR {
return &edfWrr{}
}
// edfEntry is an internal wrapper for item that also stores weight and relative position in the queue.
type edfEntry struct {
deadline float64
weight int64
orderOffset uint64
item interface{}
}
// edfPriorityQueue is a heap.Interface implementation for edfEntry elements.
type edfPriorityQueue []*edfEntry
func (pq edfPriorityQueue) Len() int { return len(pq) }
func (pq edfPriorityQueue) Less(i, j int) bool {
return pq[i].deadline < pq[j].deadline || pq[i].deadline == pq[j].deadline && pq[i].orderOffset < pq[j].orderOffset
}
func (pq edfPriorityQueue) Swap(i, j int) { pq[i], pq[j] = pq[j], pq[i] }
func (pq *edfPriorityQueue) Push(x interface{}) {
*pq = append(*pq, x.(*edfEntry))
}
func (pq *edfPriorityQueue) Pop() interface{} {
old := *pq
*pq = old[0 : len(old)-1]
return old[len(old)-1]
}
func (edf *edfWrr) Add(item interface{}, weight int64) {
edf.lock.Lock()
defer edf.lock.Unlock()
entry := edfEntry{
deadline: edf.currentTime + 1.0/float64(weight),
weight: weight,
item: item,
orderOffset: edf.currentOrderOffset,
}
edf.currentOrderOffset++
heap.Push(&edf.items, &entry)
}
func (edf *edfWrr) Next() interface{} {
edf.lock.Lock()
defer edf.lock.Unlock()
if len(edf.items) == 0 {
return nil
}
item := edf.items[0]
edf.currentTime = item.deadline
item.deadline = edf.currentTime + 1.0/float64(item.weight)
heap.Fix(&edf.items, 0)
return item.item
}
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