From bf0de16c9a6d2240316ddfd09e3b4101cc68d6b7 Mon Sep 17 00:00:00 2001
From: Mark McGranaghan <mmcgrana@gmail.com>
Date: Thu, 18 Oct 2012 19:57:28 -0400
Subject: [PATCH] publish worker-pools

---
 examples.txt                              |  3 +-
 examples/scatter-gather/scatter-gather.go | 24 ---------
 examples/worker-pools/worker-pools.go     | 61 +++++++++++++++--------
 examples/worker-pools/worker-pools.sh     | 16 ++++++
 4 files changed, 56 insertions(+), 48 deletions(-)
 delete mode 100644 examples/scatter-gather/scatter-gather.go
 create mode 100644 examples/worker-pools/worker-pools.sh

diff --git a/examples.txt b/examples.txt
index 42be2ef..1163fe2 100644
--- a/examples.txt
+++ b/examples.txt
@@ -34,11 +34,10 @@ Timeouts
 Non-Blocking Channel Operations
 Closing Channels
 Range over Channels
-# Scatter Gather
 # Rate Limiting
-# Worker Pools
 Timers
 Tickers
+Worker Pools
 # State Goroutine
 # State Mutex
 Sorting
diff --git a/examples/scatter-gather/scatter-gather.go b/examples/scatter-gather/scatter-gather.go
deleted file mode 100644
index a486e43..0000000
--- a/examples/scatter-gather/scatter-gather.go
+++ /dev/null
@@ -1,24 +0,0 @@
-package main
-
-import "sync"
-import "time"
-import "math/rand"
-import "fmt"
-
-func main() {
-    times := new([20]int)
-    wait := new(sync.WaitGroup)
-    for i := 0; i < 20; i++ {
-        n := i
-        wait.Add(1)
-        go func() {
-            opTime := time.Duration(rand.Intn(2000))
-            time.Sleep(opTime * time.Millisecond)
-            fmt.Println(n)
-            times[n] = opTime
-            wait.Done()
-        }()
-    }
-    wait.Wait()
-    fmt.Println(*times)
-}
diff --git a/examples/worker-pools/worker-pools.go b/examples/worker-pools/worker-pools.go
index 396224e..71efafb 100644
--- a/examples/worker-pools/worker-pools.go
+++ b/examples/worker-pools/worker-pools.go
@@ -1,29 +1,46 @@
+// In this example we'll look at how to implement
+// a _worker pool_ using goroutines and channels.
+
 package main
 
 import "time"
 
-func main() {
-    jobs := make(chan int, 100)
-    acks := make(chan bool, 100)
-
-    for w := 0; w < 10; w++ {
-        go func() {
-            for j := range jobs {
-                println("worker", w, "processing job", j)
-                time.Sleep(time.Millisecond * 150)
-                acks <- true
-            }
-        }()
+// Here's the worker, of which we'll run several
+// concurrent instances. These workers will receive
+// work on the `jobs` channel and send the corresponding
+// results on `results`. We'll sleep a second per job to
+// simulate an expensive task.
+func worker(id int, jobs <-chan int, results chan<- int) {
+    for j := range jobs {
+        println("worker", id, "processing job", j)
+        time.Sleep(time.Second)
+        results <- j * 2
     }
-
-    for j := 0; j < 100; j++ {
-        jobs <- j
-    }
-
-    for a := 0; a < 100; a++ {
-        <-acks
-    }
-    println("all done")
 }
 
-// todo: broken
+func main() {
+
+    // In order to use our pool of workers we need to send
+    // them work and collect their results. We make 2
+    // channels for this.
+    jobs := make(chan int, 100)
+    results := make(chan int, 100)
+
+    // This starts up 3 workers, initially blocked
+    // because there are no jobs yet.
+    for w := 1; w <= 3; w++ {
+        go worker(w, jobs, results)
+    }
+
+    // Here we send 9 `jobs` and then `close` that
+    // channel to indicate that's all the work we have.
+    for j := 1; j <= 9; j++ {
+        jobs <- j
+    }
+    close(jobs)
+
+    // Finally we collect all the results of the work.
+    for a := 1; a <= 9; a++ {
+        <-results
+    }
+}
diff --git a/examples/worker-pools/worker-pools.sh b/examples/worker-pools/worker-pools.sh
new file mode 100644
index 0000000..90937e1
--- /dev/null
+++ b/examples/worker-pools/worker-pools.sh
@@ -0,0 +1,16 @@
+# Our running program shows the 9 jobs being executed by
+# various workers. The program only takes about 3 seconds
+# despite doing about 9 seconds of total work because
+# there are 3 workers operating concurrently.
+$ time go run worker-pools.go 
+worker 1 processing job 1
+worker 2 processing job 2
+worker 3 processing job 3
+worker 1 processing job 4
+worker 2 processing job 5
+worker 3 processing job 6
+worker 1 processing job 7
+worker 2 processing job 8
+worker 3 processing job 9
+
+real	0m3.149s