README.md

@@ -36,16 +36,3 @@ select {
         // receive when c is blocked        
 }
 ```
-
-## sync.Mutex  
-
-Channels are great for communication, but what if we don't need communication?  
-
-What if we just want to make sure only one goroutine can access a variable at a time to avoid conflicts? This concept is called `mutual exclusion`, and the conventional name for the data structure that provides it is `mutex`  
-
-Go's standard library provides mutual exclusion with `sync.Mutex` and its two methods: `Lock` and `Unlock`  
-
-
-## sync.WaitGroup  
-
-https://tutorialedge.net/golang/go-waitgroup-tutorial/

basics/mutex/main.go

@@ -1,39 +0,0 @@
-package main
-
-import (
-	"fmt"
-	"sync"
-	"time"
-)
-
-// SafeCounter is safe to use concurrently.
-type SafeCounter struct {
-	mu sync.Mutex
-	v  map[string]int
-}
-
-// Inc increments the counter for the given key.
-func (c *SafeCounter) Inc(key string) {
-	c.mu.Lock()
-	// Lock so only one goroutine at a time can access the map c.v.
-	c.v[key]++
-	c.mu.Unlock()
-}
-
-// Value returns the current value of the counter for the given key.
-func (c *SafeCounter) Value(key string) int {
-	c.mu.Lock()
-	// Lock so only one goroutine at a time can access the map c.v.
-	defer c.mu.Unlock()
-	return c.v[key]
-}
-
-func main() {
-	c := SafeCounter{v: make(map[string]int)}
-	for i := 0; i < 1000; i++ {
-		go c.Inc("somekey")
-	}
-
-	time.Sleep(time.Second)
-	fmt.Println(c.Value("somekey"))
-}

exercise/web-crawler/main.go

@@ -1,120 +0,0 @@
-package main
-
-import (
-	"fmt"
-	"sync"
-)
-
-type Fetcher interface {
-	// Fetch returns the body of URL and
-	// a slice of URLs found on that page.
-	Fetch(url string) (body string, urls []string, err error)
-}
-
-type SafeCounter struct {
-	mu      sync.Mutex
-	wg      sync.WaitGroup
-	visited map[string]struct{}
-}
-
-var (
-	safeCounter *SafeCounter
-)
-
-// Crawl uses fetcher to recursively crawl
-// pages starting with url, to a maximum of depth.
-func Crawl(url string, depth int, fetcher Fetcher) {
-	// TODO: Fetch URLs in parallel.
-	// TODO: Don't fetch the same URL twice.
-	// This implementation doesn't do either:
-	defer safeCounter.wg.Done()
-
-	safeCounter.mu.Lock()
-	defer safeCounter.mu.Unlock()
-	if url != "" {
-		_, ok := safeCounter.visited[url]
-		if ok {
-			return
-		}
-		safeCounter.visited[url] = struct{}{}
-	}
-
-	if depth <= 0 {
-		safeCounter.wg.Done()
-		return
-	}
-
-	body, urls, err := fetcher.Fetch(url)
-	if err != nil {
-		fmt.Println(err)
-		return
-	}
-
-	fmt.Printf("found: %s %q\n", url, body)
-
-	for _, u := range urls {
-		safeCounter.wg.Add(1)
-		go Crawl(u, depth-1, fetcher)
-	}
-	return
-}
-
-func main() {
-	safeCounter = &SafeCounter{
-		visited: make(map[string]struct{}),
-	}
-
-	safeCounter.wg.Add(1)
-	go Crawl("https://golang.org/", 4, fetcher)
-	safeCounter.wg.Wait()
-
-}
-
-// fakeFetcher is Fetcher that returns canned results.
-type fakeFetcher map[string]*fakeResult
-
-type fakeResult struct {
-	body string
-	urls []string
-}
-
-func (f fakeFetcher) Fetch(url string) (string, []string, error) {
-	if res, ok := f[url]; ok {
-		return res.body, res.urls, nil
-	}
-	return "", nil, fmt.Errorf("not found: %s", url)
-}
-
-// fetcher is a populated fakeFetcher.
-var fetcher = fakeFetcher{
-	"https://golang.org/": &fakeResult{
-		"The Go Programming Language",
-		[]string{
-			"https://golang.org/pkg/",
-			"https://golang.org/cmd/",
-		},
-	},
-	"https://golang.org/pkg/": &fakeResult{
-		"Packages",
-		[]string{
-			"https://golang.org/",
-			"https://golang.org/cmd/",
-			"https://golang.org/pkg/fmt/",
-			"https://golang.org/pkg/os/",
-		},
-	},
-	"https://golang.org/pkg/fmt/": &fakeResult{
-		"Package fmt",
-		[]string{
-			"https://golang.org/",
-			"https://golang.org/pkg/",
-		},
-	},
-	"https://golang.org/pkg/os/": &fakeResult{
-		"Package os",
-		[]string{
-			"https://golang.org/",
-			"https://golang.org/pkg/",
-		},
-	},
-}