Rename waitgroup-->waitgroups

examples/waitgroups/waitgroups.go

@@ -0,0 +1,42 @@
+// To wait for multiple goroutines to finish, we can
+// use a *wait group*.
+
+package main
+
+import (
+    "fmt"
+    "sync"
+    "time"
+)
+
+// This is the function we'll run in every goroutine.
+// Note that a WaitGroup must be passed to functions by
+// pointer.
+func worker(id int, wg *sync.WaitGroup) {
+    fmt.Printf("Worker %d starting\n", id)
+
+    // Sleep to simulate an expensive task.
+    time.Sleep(time.Second)
+    fmt.Printf("Worker %d done\n", id)
+
+    // Notify the WaitGroup that this worker is done.
+    wg.Done()
+}
+
+func main() {
+
+    // This WaitGroup is used to wait for all the
+    // goroutines launched here to finish.
+    var wg sync.WaitGroup
+
+    // Launch several goroutines and increment the WaitGroup
+    // counter for each.
+    for i := 1; i <= 5; i++ {
+        wg.Add(1)
+        go worker(i, &wg)
+    }
+
+    // Block until the WaitGroup counter goes back to 0;
+    // all the workers notified they're done.
+    wg.Wait()
+}

examples/waitgroups/waitgroups.hash

@@ -0,0 +1,2 @@
+499c7ee59b2ae06d2d3171768d9cf11762121a87
+gLLmgcR7YkP

examples/waitgroups/waitgroups.sh

@@ -0,0 +1,14 @@
+$ go run waitgroups.go
+Worker 5 starting
+Worker 3 starting
+Worker 4 starting
+Worker 1 starting
+Worker 2 starting
+Worker 4 done
+Worker 1 done
+Worker 2 done
+Worker 5 done
+Worker 3 done
+
+# The order of workers starting up and finishing
+# is likely to be different for each invocation.