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queue.go
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queue.go
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// Copyright 2014-2021 Aerospike, 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 atomic
import "sync"
// Queue is a non-blocking FIFO queue.
// If the queue is empty, nil is returned.
// if the queue is full, offer will return false
type Queue struct {
head, tail uint32
data []interface{}
size uint32
wrapped bool
mutex sync.Mutex
}
// NewQueue creates a new queue with initial size.
func NewQueue(size int) *Queue {
if size <= 0 {
panic("Queue size cannot be less than 1")
}
return &Queue{
wrapped: false,
data: make([]interface{}, uint32(size)),
size: uint32(size),
}
}
// Offer adds an item to the queue unless the queue is full.
// In case the queue is full, the item will not be added to the queue
// and false will be returned
func (q *Queue) Offer(obj interface{}) bool {
q.mutex.Lock()
// make sure queue is not full
if q.tail == q.head && q.wrapped {
q.mutex.Unlock()
return false
}
if q.head+1 == q.size {
q.wrapped = true
}
q.head = (q.head + 1) % q.size
q.data[q.head] = obj
q.mutex.Unlock()
return true
}
// Poll removes and returns an item from the queue.
// If the queue is empty, nil will be returned.
func (q *Queue) Poll() (res interface{}) {
q.mutex.Lock()
// if queue is not empty
if q.wrapped || (q.tail != q.head) {
if q.tail+1 == q.size {
q.wrapped = false
}
q.tail = (q.tail + 1) % q.size
res = q.data[q.tail]
}
q.mutex.Unlock()
return res
}