/
queue.go
174 lines (138 loc) · 3.02 KB
/
queue.go
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/*
* Minio Client, (C) 2016 Minio, 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 cmd
import (
"encoding/json"
"fmt"
"io"
"sync"
)
// Comparer is an interface for queued objects, used to identify duplicate objects
// in queue.
type Comparer interface {
Equal(interface{}) bool
}
// Queue allows objects to be queued on a first in first out base.
type Queue struct {
a []interface{}
m sync.Mutex
i int // read index
j int // write index
idleCh chan interface{}
closed bool
}
// NewQueue creates a new queue
func NewQueue() *Queue {
return &Queue{
idleCh: make(chan interface{}),
closed: false,
}
}
// Save writes the current queue content to the writer
func (q *Queue) Save(dst io.Writer) error {
q.m.Lock()
defer q.m.Unlock()
for i := q.i; i < q.j; i++ {
jsonData, err := json.Marshal(q.a[i])
if err != nil {
return err
}
fmt.Fprintln(dst, string(jsonData))
}
return nil
}
// Wait for items to become available
func (q *Queue) Wait() error {
q.m.Lock()
if q.closed {
q.m.Unlock()
return fmt.Errorf("Channel closed")
}
if q.i < q.j {
q.m.Unlock()
return nil
}
q.m.Unlock()
_, ok := <-q.idleCh
if !ok {
return fmt.Errorf("Channel closed")
}
return nil
}
// Close and disable the queue
func (q *Queue) Close() {
q.m.Lock()
defer q.m.Unlock()
q.closed = true
close(q.idleCh)
}
// Pop the first object on the queue
func (q *Queue) Pop() interface{} {
q.m.Lock()
defer q.m.Unlock()
if q.closed {
return nil
}
if q.i >= q.j {
return nil
}
defer func() {
q.i++
}()
return q.a[q.i]
}
func (q *Queue) grow(n int) {
a := make([]interface{}, q.j+10)
// we can slide in future, for now just grow the array
copy(a[0:q.j], q.a[0:q.j])
q.a = a
}
// ErrObjectAlreadyQueued occurs when the object being pushed already exists
// in the queue
var ErrObjectAlreadyQueued = fmt.Errorf("Object already queued")
// Count returns the number of items in the queue
func (q *Queue) Count() int {
q.m.Lock()
defer q.m.Unlock()
return q.j - q.i
}
// Push a new object to the queue
func (q *Queue) Push(u interface{}) error {
q.m.Lock()
defer q.m.Unlock()
for i := q.i; i < q.j; i++ {
// prevent items not yet copied, to be queued twice
if s, ok := u.(Comparer); !ok {
// no comparer interface
break
} else if !s.Equal(q.a[i]) {
// not equal
continue
}
return ErrObjectAlreadyQueued
}
if q.j >= len(q.a) {
q.grow(10)
}
q.a[q.j] = u
q.j++
select {
case q.idleCh <- true:
default:
// non blocking send, causes wait to resume
}
return nil
}