publish select

examples.txt

@@ -31,7 +31,7 @@ Channels
 # Channel Buffering
 # Channel Directions
 # Synchronization
-# Select
+Select
 # Timeouts
 # Scatter Gather
 # Rate Limiting

examples/goroutines/goroutines.go

@@ -13,12 +13,13 @@ func f(from string) {
 func main() {
 
     // Suppose we have a function call `f(s)`. Here's how
-    // we'd call that in the usual way, running it inline.
+    // we'd call that in the usual way, running it
+    // synchronously.
     f("direct")
 
     // To invoke this function in a goroutine, use
-    // `go f(s)`. This will start a new, concurrently
-    // executing goroutine.
+    // `go f(s)`. This new goroutine will execute
+    // concurrently with the current one.
     go f("goroutine")
 
     // You can also start a goroutine for an anonymous
@@ -27,7 +28,7 @@ func main() {
         fmt.Println("going")
     }()
 
-    // Our two goroutines are running asynchrously in
+    // Our two goroutines are running asynchronously in
     // separate goroutines now, so execution falls through
     // to here. This `Scanln` code requires we press a key
     // before the program exits.

examples/goroutines/goroutines.sh

@@ -1,5 +1,5 @@
 # When we run this program, we see the output of the
-# direct call first, then the interleaved output of the
+# blocking call first, then the interleaved output of the
 # two gouroutines. This interleaving reflects the
 # goroutines being run concurrently by the Go runtime.
 $ go run goroutines.go

examples/select/select.go

@@ -1,32 +1,52 @@
+// Go's _select_ lets you wait on multiple channel
+// operations. Combining goroutines and channels with
+// select is powerful feature of Go.
+
 package main
 
 import "time"
 import "fmt"
 
 func main() {
+
+    // For our example we'll select accross two channels.
     c1 := make(chan string)
     c2 := make(chan string)
+
+    // This third channel will indicate when we're done
+    // and can exit the program.
     d := make(chan bool, 1)
 
+    // The first two channels will receive a value after
+    // some amount of time, to simulate e.g. blocking RPC
+    // operations executing in concurrent goroutines.
     go func() {
         time.Sleep(time.Second * 1)
-        c1 <- "from 1"
+        c1 <- "one"
     }()
     go func() {
         time.Sleep(time.Second * 2)
-        c2 <- "from 2"
+        c2 <- "two"
     }()
 
+    // We'll use `select` to await both of these values
+    // simultaneously, printing each one as it arrives.
+    // Once we've received both, we'll send a value to the
+    // `d` channel indicating that we're ready to proceed.
     go func() {
         for i := 0; i < 2; i++ {
             select {
             case msg1 := <-c1:
-                fmt.Println(msg1)
+                fmt.Println("received", msg1)
             case msg2 := <-c2:
-                fmt.Println(msg2)
+                fmt.Println("received", msg2)
             }
         }
         d <- true
     }()
+
+    // Since all other code is running in concurrent
+    // goroutines, we'll executing a blocking receive
+    // here to await completion of our example.
     <-d
 }

examples/select/select.sh

@@ -0,0 +1,10 @@
+# We receive the values `"one"` and then `"two"` as
+# expected.
+$ time go run select.go 
+received one
+received two
+
+# Note that the total execution time is only ~2 seconds
+# since both the 1 and 2 second `Sleeps` execute
+# concurrently.
+real	0m2.245s