Releasing a high-performance goroutine pool in Go
Tags: go, goroutine
Published: 2019-10-02 16:18:57

# ants
<p align="center">
<img src="https://user-images.githubusercontent.com/7496278/51748488-8efd2600-20e7-11e9-91f5-1c5b466dcca1.jpg"/>
A goroutine pool for Go
<br/><br/>
<a title="Build Status" target="_blank" href="https://travis-ci.com/panjf2000/ants"><img src="https://img.shields.io/travis/com/panjf2000/ants?style=flat-square"></a>
<a title="Codecov" target="_blank" href="https://codecov.io/gh/panjf2000/ants"><img src="https://img.shields.io/codecov/c/github/panjf2000/ants?style=flat-square"></a>
<a title="Go Report Card" target="_blank" href="https://goreportcard.com/report/github.com/panjf2000/ants"><img src="https://goreportcard.com/badge/github.com/panjf2000/ants?style=flat-square"></a>
<a title="Ants on Sourcegraph" target="_blank" href="https://sourcegraph.com/github.com/panjf2000/ants?badge"><img src="https://sourcegraph.com/github.com/panjf2000/ants/-/badge.svg?style=flat-square"></a>
<br/>
<a title="" target="_blank" href="https://golangci.com/r/github.com/panjf2000/ants"><img src="https://golangci.com/badges/github.com/panjf2000/ants.svg"></a>
<a title="Godoc for ants" target="_blank" href="https://godoc.org/github.com/panjf2000/ants"><img src="https://img.shields.io/badge/go-documentation-blue.svg?style=flat-square"></a>
<a title="Release" target="_blank" href="https://github.com/panjf2000/ants/releases"><img src="https://img.shields.io/github/release/panjf2000/ants.svg?style=flat-square"></a>
<a title="License" target="_blank" href="https://opensource.org/licenses/mit-license.php"><img src="https://img.shields.io/aur/license/pac?style=flat-square"></a>
</p>

Github Page:
https://github.com/panjf2000/ants

Library `ants` implements a goroutine pool with fixed capacity, managing and recycling a massive number of goroutines, allowing developers to limit the number of goroutines in your concurrent programs.

## Features:

- Automatically managing and recycling a massive number of goroutines.
- Periodically purging overdue goroutines.
- Friendly interfaces: submitting tasks, getting the number of running goroutines, tuning capacity of pool dynamically, closing pool.
- Handle panic gracefully to prevent programs from crash.
- Efficient in memory usage and it even achieves higher performance than unlimited goroutines in golang.
- Nonblocking mechanism.

## Tested in the following Golang versions:

- 1.8.x
- 1.9.x
- 1.10.x
- 1.11.x
- 1.12.x
- 1.13.x


## How to install

``` sh
go get -u github.com/panjf2000/ants
```

## How to use
Just take a imagination that your program starts a massive number of goroutines, resulting in a huge consumption of memory. To mitigate that kind of situation, all you need to do is to import `ants` package and submit all your tasks to a default pool with fixed capacity, activated when package `ants` is imported:

``` go
package main

import (
	"fmt"
	"sync"
	"sync/atomic"
	"time"

	"github.com/panjf2000/ants/v2"
)

var sum int32

func myFunc(i interface{}) {
	n := i.(int32)
	atomic.AddInt32(&sum, n)
	fmt.Printf("run with %d\n", n)
}

func demoFunc() {
	time.Sleep(10 * time.Millisecond)
	fmt.Println("Hello World!")
}

func main() {
	defer ants.Release()

	runTimes := 1000

	// Use the common pool.
	var wg sync.WaitGroup
	syncCalculateSum := func() {
		demoFunc()
		wg.Done()
	}
	for i := 0; i < runTimes; i++ {
		wg.Add(1)
		_ = ants.Submit(syncCalculateSum)
	}
	wg.Wait()
	fmt.Printf("running goroutines: %d\n", ants.Running())
	fmt.Printf("finish all tasks.\n")

	// Use the pool with a function,
	// set 10 to the capacity of goroutine pool and 1 second for expired duration.
	p, _ := ants.NewPoolWithFunc(10, func(i interface{}) {
		myFunc(i)
		wg.Done()
	})
	defer p.Release()
	// Submit tasks one by one.
	for i := 0; i < runTimes; i++ {
		wg.Add(1)
		_ = p.Invoke(int32(i))
	}
	wg.Wait()
	fmt.Printf("running goroutines: %d\n", p.Running())
	fmt.Printf("finish all tasks, result is %d\n", sum)
}
```

## Integrate with http server
```go
package main

import (
	"io/ioutil"
	"net/http"

	"github.com/panjf2000/ants/v2"
)

type Request struct {
	Param  []byte
	Result chan []byte
}

func main() {
  pool, _ := ants.NewPoolWithFunc(100000, func(payload interface{}) {
		request, ok := payload.(*Request)
		if !ok {
			return
		}
		reverseParam := func(s []byte) []byte {
			for i, j := 0, len(s)-1; i < j; i, j = i+1, j-1 {
				s[i], s[j] = s[j], s[i]
			}
			return s
		}(request.Param)

		request.Result <- reverseParam
  })
	defer pool.Release()

	http.HandleFunc("/reverse", func(w http.ResponseWriter, r *http.Request) {
		param, err := ioutil.ReadAll(r.Body)
		if err != nil {
			http.Error(w, "request error", http.StatusInternalServerError)
		}
		defer r.Body.Close()

		request := &Request{Param: param, Result: make(chan []byte)}

		// Throttle the requests traffic with ants pool. This process is asynchronous and
		// you can receive a result from the channel defined outside.
		if err := pool.Invoke(request); err != nil {
			http.Error(w, "throttle limit error", http.StatusInternalServerError)
		}

		w.Write(<-request.Result)
	})

	http.ListenAndServe(":8080", nil)
}
```

## Functional options for ants pool

```go
type Options struct {
	// ExpiryDuration set the expired time (second) of every worker.
	ExpiryDuration time.Duration

	// PreAlloc indicate whether to make memory pre-allocation when initializing Pool.
	PreAlloc bool

	// Max number of goroutine blocking on pool.Submit.
	// 0 (default value) means no such limit.
	MaxBlockingTasks int

	// When Nonblocking is true, Pool.Submit will never be blocked.
	// ErrPoolOverload will be returned when Pool.Submit cannot be done at once.
	// When Nonblocking is true, MaxBlockingTasks is inoperative.
	Nonblocking bool

	// PanicHandler is used to handle panics from each worker goroutine.
	// if nil, panics will be thrown out again from worker goroutines.
	PanicHandler func(interface{})
}

func WithOptions(options Options) Option {
	return func(opts *Options) {
		*opts = options
	}
}

func WithExpiryDuration(expiryDuration time.Duration) Option {
	return func(opts *Options) {
		opts.ExpiryDuration = expiryDuration
	}
}

func WithPreAlloc(preAlloc bool) Option {
	return func(opts *Options) {
		opts.PreAlloc = preAlloc
	}
}

func WithMaxBlockingTasks(maxBlockingTasks int) Option {
	return func(opts *Options) {
		opts.MaxBlockingTasks = maxBlockingTasks
	}
}

func WithNonblocking(nonblocking bool) Option {
	return func(opts *Options) {
		opts.Nonblocking = nonblocking
	}
}

func WithPanicHandler(panicHandler func(interface{})) Option {
	return func(opts *Options) {
		opts.PanicHandler = panicHandler
	}
}
```

`ants.Options`contains all optional configurations of ants pool, which allows you to customize the goroutine pool by invoking option functions to set up each configuration in `NewPool`/`NewPoolWithFunc`method.

## Customize limited pool

`ants` also supports customizing the capacity of pool. You can invoke the `NewPool` method to instantiate a pool with a given capacity, as following:

``` go
// Set 10000 the size of goroutine pool
p, _ := ants.NewPool(10000)
```

## Submit tasks
Tasks can be submitted by calling `ants.Submit(func())`
```go
ants.Submit(func(){})
```

## Tune pool capacity in runtime
You can tune the capacity of  `ants` pool in runtime with `Tune(int)`:

``` go
pool.Tune(1000) // Tune its capacity to 1000
pool.Tune(100000) // Tune its capacity to 100000
```

Don't worry about the synchronous problems in this case, the method here is thread-safe (or should be called goroutine-safe).

## Pre-malloc goroutine queue in pool

`ants` allows you to pre-allocate memory of goroutine queue in pool, which may get a performance enhancement under some special certain circumstances such as the scenario that requires a pool with ultra-large capacity, meanwhile each task in goroutine lasts for a long time, in this case, pre-mallocing will reduce a lot of costs when re-slicing goroutine queue.

```go
// ants will pre-malloc the whole capacity of pool when you invoke this method
p, _ := ants.NewPool(100000, ants.WithPreAlloc(true))
```

## Release Pool

```go
pool.Release()
```

## About sequence
All tasks submitted to `ants` pool will not be guaranteed to be addressed in order, because those tasks scatter among a series of concurrent workers, thus those tasks would be executed concurrently.

## Benchmarks

<div align="center"><img src="https://user-images.githubusercontent.com/7496278/51515466-c7ce9e00-1e4e-11e9-89c4-bd3785b3c667.png"/></div>
 In this benchmark-picture, the first and second benchmarks performed test cases with 1M tasks and the rest of benchmarks performed test cases with 10M tasks, both in unlimited goroutines and `ants` pool, and the capacity of this `ants` goroutine-pool was limited to 50K.

- BenchmarkGoroutine-4 represents the benchmarks with unlimited goroutines in golang.

- BenchmarkPoolGroutine-4 represents the benchmarks with a `ants` pool.

### Benchmarks with Pool 

![](https://user-images.githubusercontent.com/7496278/51515499-f187c500-1e4e-11e9-80e5-3df8f94fa70f.png)

In above benchmark picture, the first and second benchmarks performed test cases with 1M tasks and the rest of benchmarks performed test cases with 10M tasks, both in unlimited goroutines and `ants` pool, and the capacity of this `ants` goroutine-pool was limited to 50K.

**As you can see, `ants` performs 2 times faster than goroutines without pool (10M tasks) and it only consumes half the memory comparing with goroutines without pool. (both in 1M and 10M tasks)**

### Benchmarks with PoolWithFunc

![](https://user-images.githubusercontent.com/7496278/51515565-1e3bdc80-1e4f-11e9-8a08-452ab91d117e.png)

### Throughput (it is suitable for scenarios where tasks are submitted asynchronously without waiting for the final results) 

#### 100K tasks

![](https://user-images.githubusercontent.com/7496278/51515590-36abf700-1e4f-11e9-91e4-7bd3dcb5f4a5.png)

#### 1M tasks

![](https://user-images.githubusercontent.com/7496278/51515596-44617c80-1e4f-11e9-89e3-01e19d2979a1.png)

#### 10M tasks

![](https://user-images.githubusercontent.com/7496278/52987732-537c2000-3437-11e9-86a6-177f00d7a1d6.png)

### Performance Summary

![](https://user-images.githubusercontent.com/7496278/63449727-3ae6d400-c473-11e9-81e3-8b3280d8288a.gif)

**In conclusion, `ants` performs 2~6 times faster than goroutines without a pool and the memory consumption is reduced by 10 to 20 times.**

# License

Source code in `gnet` is available under the MIT [License](/LICENSE).

# Relevant Articles

-  [Goroutine 并发调度模型深度解析之手撸一个高性能协程池](https://taohuawu.club/high-performance-implementation-of-goroutine-pool)

# Users of ants (please feel free to add your projects here ~~)

[![](https://raw.githubusercontent.com/panjf2000/gnet/master/logo.png)](https://github.com/panjf2000/gnet)