Practice concurrency in golang

Uploading some snippets I created to help me better understand concurrency in
general and specifically concurrency in golang.

go/.envrc

@@ -0,0 +1 @@
+eval "$(lorri direnv)"

go/atomic-counters.go

@@ -0,0 +1,26 @@
+// Attempting to apply some of the lessons I learned here:
+// https://gobyexample.com/atomic-counters
+package main
+
+import (
+	"fmt"
+	"sync"
+	"sync/atomic"
+)
+
+func main() {
+	var count uint64
+	var wg sync.WaitGroup
+
+	for i := 0; i < 50; i += 1 {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for j := 0; j < 1000; j += 1 {
+				atomic.AddUint64(&count, 1)
+			}
+		}()
+	}
+	wg.Wait()
+	fmt.Println("Count: ", count)
+}

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))
+}

go/mutex.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+	"fmt"
+	"math/rand"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+func main() {
+	state := make(map[int]int)
+	mux := &sync.Mutex{}
+
+	var readOps uint64
+	var writeOps uint64
+
+	// Read from state
+	for i := 0; i < 1000; i += 1 {
+		for j := 0; j < 100; j += 1 {
+			go func() {
+				key := rand.Intn(5)
+				mux.Lock()
+				fmt.Printf("state[%d] = %d\n", key, state[key])
+				mux.Unlock()
+				atomic.AddUint64(&readOps, 1)
+				time.Sleep(time.Millisecond)
+			}()
+		}
+	}
+
+	// Write to state
+	for i := 0; i < 10; i += 1 {
+		for j := 0; j < 100; j += 1 {
+			go func() {
+				key := rand.Intn(5)
+				mux.Lock()
+				state[key] += 1
+				mux.Unlock()
+				fmt.Printf("Wrote to state[%d].\n", key)
+				atomic.AddUint64(&writeOps, 1)
+				time.Sleep(time.Millisecond)
+			}()
+		}
+	}
+
+	time.Sleep(time.Millisecond)
+
+	mux.Lock()
+	fmt.Printf("State: %v\n", state)
+	mux.Unlock()
+	fmt.Printf("Reads: %d\tWrites: %d\n", atomic.LoadUint64(&readOps), atomic.LoadUint64(&writeOps))
+}

go/shell.nix

@@ -0,0 +1,9 @@
+{ pkgs ? import <nixpkgs> {}, ... }:
+
+pkgs.mkShell {
+  buildInputs = [
+    pkgs.go
+    pkgs.goimports
+    pkgs.godef
+  ];
+}

go/waitgroups.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"fmt"
+	"sync"
+	"time"
+)
+
+func saySomething(x string, wg *sync.WaitGroup) {
+	defer wg.Done()
+	fmt.Println(x)
+	time.Sleep(time.Second)
+	fmt.Printf("Finished saying \"%s\"\n", x)
+}
+
+func main() {
+	var wg sync.WaitGroup
+	var things = [5]string{"chicken", "panini", "cheeseburger", "rice", "bread"}
+	for i := 0; i < 5; i += 1 {
+		wg.Add(1)
+		go saySomething(things[i], &wg)
+	}
+	wg.Wait()
+}