added init and sem

init/main.go

@@ -0,0 +1,13 @@
+package main
+
+import (
+	"github.com/davecgh/go-spew/spew"
+)
+
+func init() {
+	spew.Dump("inited")
+}
+
+func main() {
+	spew.Dump("Test")
+}

semaphore/main.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+	"fmt"
+	"sync"
+	"time"
+)
+
+func main() {
+
+	// a blocking channel to keep concurrency under control
+	semaphoreChan := make(chan struct{}, 10)
+	defer close(semaphoreChan)
+
+	// a wait group enables the main process a wait for goroutines to finish
+	wg := sync.WaitGroup{}
+
+	// a simple loop from 1 to 10
+	for i := 1; i <= 100; i++ {
+
+		// increment the wait group internal counter
+		wg.Add(1)
+
+		// print what we're about to be doing (will keep the order)
+		fmt.Printf("About to run #%d in a goroutine\n", i)
+
+		// fire off a goroutine with the index in a closure since it will be modified
+		go func(i int) {
+
+			// block until the semaphore channel has room
+			// this could also be moved out of the goroutine
+			// which would make sense if the list is huge
+			semaphoreChan <- struct{}{}
+
+			// pretend to do some synchronous work
+			time.Sleep(time.Second)
+
+			// tell the wait group that we be done
+			wg.Done()
+
+			// print an message containing the index (won't keep order)
+			fmt.Printf("About to exit #%d from a goroutine\n", i)
+
+			// clear a spot in the semaphore channel
+			<-semaphoreChan
+
+		}(i)
+	}
+
+	// wait for all the goroutines to be done
+	wg.Wait()
+}