From eaf058c8602c1b0800f8114007807563f2934725 Mon Sep 17 00:00:00 2001
From: Jian Han <jian.han@neds.com>
Date: Tue, 7 Nov 2017 14:41:25 +1000
Subject: [PATCH] added worker pool

---
 workerpool/main.go | 113 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100644 workerpool/main.go

diff --git a/workerpool/main.go b/workerpool/main.go
new file mode 100644
index 0000000..26dfc75
--- /dev/null
+++ b/workerpool/main.go
@@ -0,0 +1,113 @@
+package main
+
+import (
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/labstack/gommon/log"
+)
+
+type Task struct {
+	Err error
+	f   func() error
+}
+
+func NewTask(f func() error) *Task {
+	return &Task{f: f}
+}
+
+func (t *Task) Run(wg *sync.WaitGroup) {
+	t.Err = t.f()
+	wg.Done()
+}
+
+type Pool struct {
+	Tasks       []*Task
+	concurrency int
+	tasksChan   chan *Task
+	wg          sync.WaitGroup
+}
+
+func NewPool(tasks []*Task, concurrency int) *Pool {
+	return &Pool{
+		Tasks:       tasks,
+		concurrency: concurrency,
+		tasksChan:   make(chan *Task),
+	}
+}
+
+// Run runs all work within the pool and blocks until it's
+// finished.
+func (p *Pool) Run() {
+	for i := 0; i < p.concurrency; i++ {
+		go p.work()
+	}
+
+	p.wg.Add(len(p.Tasks))
+	for _, task := range p.Tasks {
+		p.tasksChan <- task
+	}
+
+	// all workers return
+	close(p.tasksChan)
+
+	p.wg.Wait()
+}
+
+// The work loop for any single goroutine.
+func (p *Pool) work() {
+	for task := range p.tasksChan {
+		task.Run(&p.wg)
+	}
+}
+
+func main() {
+	f1 := func() error {
+		fmt.Println("F1 Ran")
+		time.Sleep(1 * time.Second)
+		fmt.Println("F1 finished")
+		return nil
+	}
+
+	f2 := func() error {
+		fmt.Println("F2 Ran")
+		time.Sleep(2 * time.Second)
+		fmt.Println("F2 finished")
+		return nil
+	}
+	f3 := func() error {
+		fmt.Println("F3 Ran")
+		time.Sleep(1 * time.Second)
+		fmt.Println("F3 finished")
+		return nil
+	}
+
+	f4 := func() error {
+		fmt.Println("F4 Ran")
+		time.Sleep(2 * time.Second)
+		fmt.Println("F4 finished")
+		return nil
+	}
+	tasks := []*Task{
+		NewTask(f1),
+		NewTask(f2),
+		NewTask(f3),
+		NewTask(f4),
+	}
+
+	p := NewPool(tasks, 4)
+	p.Run()
+
+	var numErrors int
+	for _, task := range p.Tasks {
+		if task.Err != nil {
+			log.Error(task.Err)
+			numErrors++
+		}
+		if numErrors >= 10 {
+			log.Error("Too many errors.")
+			break
+		}
+	}
+}