From e9744427aa678754793a8ea9e9d1d9021a3d565a Mon Sep 17 00:00:00 2001
From: Mark McGranaghan <mmcgrana@gmail.com>
Date: Fri, 21 Sep 2012 08:13:55 -0700
Subject: [PATCH] synchronization

---
 039-synchronization.go | 31 ++++++++++++++++++-------------
 040-select.go          |  4 ++--
 2 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/039-synchronization.go b/039-synchronization.go
index 2d52a04..acbe6d8 100644
--- a/039-synchronization.go
+++ b/039-synchronization.go
@@ -1,18 +1,23 @@
-package main
-
-import "fmt"
+package main                     // We can use channels to synchronize execution
+                                 // accross goroutings. Here's an example of waiting
+import "fmt"                     // for another gorouting to finish.
 import "time"
 
-func printer(done chan<- bool) {
-    for i := 0; i < 10; i++ {
-		time.Sleep(time.Millisecond * 100)
-        fmt.Println(i)
-    }
-	done <- true
+func worker(done chan<- bool) {  // The `done` channel will be used for
+    fmt.Print("Working...")      // synchronization.
+    time.Sleep(time.Second)
+    fmt.Println(" done")
+	done <- true                 // Send a value to notify that the work is done.
 }
 
 func main() {
-	done := make(chan bool, 1)
-    go printer(done)
-	<- done
-}
+	done := make(chan bool, 1)   // Start a worker goroutine, give it the channel to
+    go worker(done)              // notify on.
+
+	<- done                      // Block until we can receive a value from the worker
+}                                // over the channel.
+
+/*
+$ go run synchronization.go      // If you commented out the `<- done` line, the
+Working... done                  // program would exit before the `worker` even
+*/                               // started.
diff --git a/040-select.go b/040-select.go
index fe78174..6698196 100644
--- a/040-select.go
+++ b/040-select.go
@@ -8,11 +8,11 @@ func main() {
 	d  := make(chan bool, 1)
 
     go func() {
-        time.Sleep(time.Millisecond * 1500)
+        time.Sleep(time.Second * 1)
 		c1 <- "from 1"
     }()
     go func() {
-        time.Sleep(time.Millisecond * 2000)
+        time.Sleep(time.Second * 2)
 		c2 <- "from 2"
     }()