Fix lecture

lectures/05-concurrency/lectures.slide

@@ -3,6 +3,11 @@ Concurrency with Shared Memory
 
 Фёдор Короткий
 
+* Concurrency with Shared Memory
+
+- Принципы синхронизации, такие же как в C++ или java.
+- Различается набор инструментов в стандартной библиотеке.
+
 * Happens Before
 
 - Одно событие в программе может _произойти_раньше_ (_happens_before_) другого события.
@@ -296,3 +301,36 @@ Concurrency with Shared Memory
 
 .play synconce/map.go /type result/,/OMIT/
 
+* sync.Cond
+
+  type Once struct {
+      done, running bool
+      mu            sync.Mutex
+      cond          *sync.Cond
+  }
+
+  func (once *Once) Do(f func()) {
+      once.mu.Lock()
+      defer once.mu.Unlock()
+      if done {
+          return
+      }
+      if running {
+          once.cond.Wait() // releases and acquires mutex
+          return
+      }
+      running = true
+      once.mu.Unlock()
+      f()
+      once.mu.Lock()
+      done = true
+      once.cond.Broadcast()
+  }
+
+* golang.org/x/sync
+
+Пакеты в golang.org/x содержат код, который не вошёл в стандартную библиотеку.
+
+- errgroup - `sync.WaitGroup` в встроенной обработкой ошибок
+- semaphore - семафор
+- singleflight - дедубликация вызовов

lectures/05-concurrency/memo1/memo_test.go

@@ -1,67 +0,0 @@
-// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
-// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
-
-package memo_test
-
-import (
-	"testing"
-
-	"gopl.io/ch9/memo1"
-	"gopl.io/ch9/memotest"
-)
-
-var httpGetBody = memotest.HTTPGetBody
-
-func Test(t *testing.T) {
-	m := memo.New(httpGetBody)
-	memotest.Sequential(t, m)
-}
-
-// NOTE: not concurrency-safe!  Test fails.
-func TestConcurrent(t *testing.T) {
-	m := memo.New(httpGetBody)
-	memotest.Concurrent(t, m)
-}
-
-/*
-//!+output
-$ go test -v gopl.io/ch9/memo1
-=== RUN   Test
-https://golang.org, 175.026418ms, 7537 bytes
-https://godoc.org, 172.686825ms, 6878 bytes
-https://play.golang.org, 115.762377ms, 5767 bytes
-http://gopl.io, 749.887242ms, 2856 bytes
-
-https://golang.org, 721ns, 7537 bytes
-https://godoc.org, 152ns, 6878 bytes
-https://play.golang.org, 205ns, 5767 bytes
-http://gopl.io, 326ns, 2856 bytes
---- PASS: Test (1.21s)
-PASS
-ok  gopl.io/ch9/memo1	1.257s
-//!-output
-*/
-
-/*
-//!+race
-$ go test -run=TestConcurrent -race -v gopl.io/ch9/memo1
-=== RUN   TestConcurrent
-...
-WARNING: DATA RACE
-Write by goroutine 36:
-  runtime.mapassign1()
-      ~/go/src/runtime/hashmap.go:411 +0x0
-  gopl.io/ch9/memo1.(*Memo).Get()
-      ~/gobook2/src/gopl.io/ch9/memo1/memo.go:32 +0x205
-  ...
-
-Previous write by goroutine 35:
-  runtime.mapassign1()
-      ~/go/src/runtime/hashmap.go:411 +0x0
-  gopl.io/ch9/memo1.(*Memo).Get()
-      ~/gobook2/src/gopl.io/ch9/memo1/memo.go:32 +0x205
-...
-Found 1 data race(s)
-FAIL	gopl.io/ch9/memo1	2.393s
-//!-race
-*/

lectures/05-concurrency/memo2/memo_test.go

@@ -1,23 +0,0 @@
-// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
-// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
-
-package memo_test
-
-import (
-	"testing"
-
-	"gopl.io/ch9/memo2"
-	"gopl.io/ch9/memotest"
-)
-
-var httpGetBody = memotest.HTTPGetBody
-
-func Test(t *testing.T) {
-	m := memo.New(httpGetBody)
-	memotest.Sequential(t, m)
-}
-
-func TestConcurrent(t *testing.T) {
-	m := memo.New(httpGetBody)
-	memotest.Concurrent(t, m)
-}

lectures/05-concurrency/memo3/memo_test.go

@@ -1,23 +0,0 @@
-// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
-// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
-
-package memo_test
-
-import (
-	"testing"
-
-	"gopl.io/ch9/memo3"
-	"gopl.io/ch9/memotest"
-)
-
-var httpGetBody = memotest.HTTPGetBody
-
-func Test(t *testing.T) {
-	m := memo.New(httpGetBody)
-	memotest.Sequential(t, m)
-}
-
-func TestConcurrent(t *testing.T) {
-	m := memo.New(httpGetBody)
-	memotest.Concurrent(t, m)
-}

lectures/05-concurrency/memo4/memo_test.go

@@ -1,23 +0,0 @@
-// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
-// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
-
-package memo_test
-
-import (
-	"testing"
-
-	"gopl.io/ch9/memo4"
-	"gopl.io/ch9/memotest"
-)
-
-var httpGetBody = memotest.HTTPGetBody
-
-func Test(t *testing.T) {
-	m := memo.New(httpGetBody)
-	memotest.Sequential(t, m)
-}
-
-func TestConcurrent(t *testing.T) {
-	m := memo.New(httpGetBody)
-	memotest.Concurrent(t, m)
-}