subtree(users/wpcarro): docking briefcase at '24f5a642'

git-subtree-dir: users/wpcarro
git-subtree-mainline: 464bbcb15c
git-subtree-split: 24f5a642af
Change-Id: I6105b3762b79126b3488359c95978cadb3efa789

users/wpcarro/go/channels.go

@@ -0,0 +1,81 @@
+package main
+
+import (
+	"fmt"
+	"math/rand"
+	"sync"
+	"sync/atomic"
+)
+
+type readMsg struct {
+	key    int
+	sender chan int
+}
+
+type writeMsg struct {
+	key    int
+	value  int
+	sender chan bool
+}
+
+func main() {
+	fmt.Println("Hello, go.")
+
+	var readOps uint64
+	var writeOps uint64
+	var wg sync.WaitGroup
+
+	reads := make(chan readMsg)
+	writes := make(chan writeMsg)
+
+	go func() {
+		state := make(map[int]int)
+		for {
+			select {
+			case msg := <-reads:
+				msg.sender <- state[msg.key]
+			case msg := <-writes:
+				state[msg.key] = msg.value
+				msg.sender <- true
+			}
+		}
+	}()
+
+	// Reads
+	for i := 0; i < 100; i += 1 {
+		go func() {
+			wg.Add(1)
+			defer wg.Done()
+			for j := 0; j < 100; j += 1 {
+				msg := readMsg{
+					key:    rand.Intn(5),
+					sender: make(chan int)}
+				reads <- msg
+				val := <-msg.sender
+				fmt.Printf("Received %d.\n", val)
+				atomic.AddUint64(&readOps, 1)
+			}
+		}()
+	}
+
+	// Writes
+	for i := 0; i < 100; i += 1 {
+		go func() {
+			wg.Add(1)
+			defer wg.Done()
+			for j := 0; j < 100; j += 1 {
+				msg := writeMsg{
+					key:    rand.Intn(5),
+					value:  rand.Intn(10),
+					sender: make(chan bool)}
+				writes <- msg
+				<-msg.sender
+				fmt.Printf("Set %d as %d in state\n", msg.key, msg.value)
+				atomic.AddUint64(&writeOps, 1)
+			}
+		}()
+	}
+
+	wg.Wait()
+	fmt.Printf("Read ops: %d\tWrite ops: %d\n", atomic.LoadUint64(&readOps), atomic.LoadUint64(&writeOps))
+}