queue

package
Version: v0.0.0-...-59788d5 Latest Latest
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Published: Feb 11, 2015 License: Apache-2.0 Imports: 5 Imported by: 0

Documentation

Overview

The priority queue is almost a spitting image of the logic used for a regular queue. In order to keep the logic fast, this code is repeated instead of using casts to cast to interface{} back and forth. If Go had inheritance and generics, this problem would be easier to solve.

Package queue includes a regular queue and a priority queue. These queues rely on waitgroups to pause listening threads on empty queues until a message is received. If any thread calls Dispose on the queue, any listeners are immediately returned with an error. Any subsequent put to the queue will return an error as opposed to panicking as with channels. Queues will grow with unbounded behavior as opposed to channels which can be buffered but will pause while a thread attempts to put to a full channel.

Recently added is a lockless ring buffer using the same basic C design as found here:

http://www.1024cores.net/home/lock-free-algorithms/queues/bounded-mpmc-queue

Modified for use with Go with the addition of some dispose semantics providing the capability to release blocked threads. This works for both puts and gets, either will return an error if they are blocked and the buffer is disposed. This could serve as a signal to kill a goroutine. All threadsafety is acheived using CAS operations, making this buffer pretty quick.

Benchmarks: BenchmarkPriorityQueue-8 2000000 782 ns/op BenchmarkQueue-8 2000000 671 ns/op BenchmarkChannel-8 1000000 2083 ns/op BenchmarkQueuePut-8 20000 84299 ns/op BenchmarkQueueGet-8 20000 80753 ns/op BenchmarkExecuteInParallel-8 20000 68891 ns/op BenchmarkRBLifeCycle-8 10000000 177 ns/op BenchmarkRBPut-8 30000000 58.1 ns/op BenchmarkRBGet-8 50000000 26.8 ns/op

TODO: We really need a Fibonacci heap for the priority queue. TODO: Unify the types of queue to the same interface.

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.

Index

Constants

This section is empty.

Variables

This section is empty.

Functions

func ExecuteInParallel

func ExecuteInParallel(q *Queue, fn func(interface{}))

ExecuteInParallel will (in parallel) call the provided function with each item in the queue until the queue is exhausted. When the queue is exhausted execution is complete and all goroutines will be killed. This means that the queue will be disposed so cannot be used again.

Types

type Item

type Item interface {
	// Compare returns a bool that can be used to determine
	// ordering in the priority queue.  Assuming the queue
	// is in ascending order, this should return > logic.
	// Return 1 to indicate this object is greater than the
	// the other logic, 0 to indicate equality, and -1 to indicate
	// less than other.
	Compare(other Item) int
}

Item is an item that can be added to the priority queue.

type PriorityQueue

type PriorityQueue struct {
	// contains filtered or unexported fields
}

PriorityQueue is similar to queue except that it takes items that implement the Item interface and adds them to the queue in priority order.

func NewPriorityQueue

func NewPriorityQueue(hint int) *PriorityQueue

NewPriorityQueue is the constructor for a priority queue.

func (*PriorityQueue) Dispose

func (pq *PriorityQueue) Dispose()

Dispose will prevent any further reads/writes to this queue and frees available resources.

func (*PriorityQueue) Disposed

func (pq *PriorityQueue) Disposed() bool

Disposed returns a bool indicating if this queue has been disposed.

func (*PriorityQueue) Empty

func (pq *PriorityQueue) Empty() bool

Empty returns a bool indicating if there are any items left in the queue.

func (*PriorityQueue) Get

func (pq *PriorityQueue) Get(number int) ([]Item, error)

Get retrieves items from the queue. If the queue is empty, this call blocks until the next item is added to the queue. This will attempt to retrieve number of items.

func (*PriorityQueue) Len

func (pq *PriorityQueue) Len() int

Len returns a number indicating how many items are in the queue.

func (*PriorityQueue) Peek

func (pq *PriorityQueue) Peek() Item

Peek will look at the next item without removing it from the queue.

func (*PriorityQueue) Put

func (pq *PriorityQueue) Put(items ...Item) error

Put adds items to the queue.

type Queue

type Queue struct {
	// contains filtered or unexported fields
}

Queue is the struct responsible for tracking the state of the queue.

func New

func New(hint int64) *Queue

New is a constructor for a new threadsafe queue.

func (*Queue) Dispose

func (q *Queue) Dispose()

Dispose will dispose of this queue. Any subsequent calls to Get or Put will return an error.

func (*Queue) Disposed

func (q *Queue) Disposed() bool

Disposed returns a bool indicating if this queue has had disposed called on it.

func (*Queue) Empty

func (q *Queue) Empty() bool

Empty returns a bool indicating if this bool is empty.

func (*Queue) Get

func (q *Queue) Get(number int64) ([]interface{}, error)

Get will add an item to the queue. If there are some items in the queue, get will return a number UP TO the number passed in as a parameter. If no items are in the queue, this method will pause until items are added to the queue.

func (*Queue) Len

func (q *Queue) Len() int64

Len returns the number of items in this queue.

func (*Queue) Put

func (q *Queue) Put(items ...interface{}) error

Put will add the specified items to the queue.

func (*Queue) TakeUntil

func (q *Queue) TakeUntil(checker func(item interface{}) bool) ([]interface{}, error)

TakeUntil takes a function and returns a list of items that match the checker until the checker returns false. This does not wait if there are no items in the queue.

type RingBuffer

type RingBuffer struct {
	// contains filtered or unexported fields
}

RingBuffer is a MPMC buffer that achieves threadsafety with CAS operations only. A put on full or get on empty call will block until an item is put or retrieved. Calling Dispose on the RingBuffer will unblock any blocked threads with an error. This buffer is similar to the buffer described here: http://www.1024cores.net/home/lock-free-algorithms/queues/bounded-mpmc-queue with some minor additions.

func NewRingBuffer

func NewRingBuffer(size uint64) *RingBuffer

NewRingBuffer will allocate, initialize, and return a ring buffer with the specified size.

func (*RingBuffer) Cap

func (rb *RingBuffer) Cap() uint64

Cap returns the capacity of this ring buffer.

func (*RingBuffer) Dispose

func (rb *RingBuffer) Dispose()

Dispose will dispose of this queue and free any blocked threads in the Put and/or Get methods. Calling those methods on a disposed queue will return an error.

func (*RingBuffer) Get

func (rb *RingBuffer) Get() (interface{}, error)

Get will return the next item in the queue. This call will block if the queue is empty. This call will unblock when an item is added to the queue or Dispose is called on the queue. An error will be returned if the queue is disposed.

func (*RingBuffer) IsDisposed

func (rb *RingBuffer) IsDisposed() bool

IsDisposed will return a bool indicating if this queue has been disposed.

func (*RingBuffer) Len

func (rb *RingBuffer) Len() uint64

Len returns the number of items in the queue.

func (*RingBuffer) Put

func (rb *RingBuffer) Put(item interface{}) error

Put adds the provided item to the queue. If the queue is full, this call will block until an item is added to the queue or Dispose is called on the queue. An error will be returned if the queue is disposed.

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