Add waitgroup.
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29
waitgroup/README.md
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waitgroup/README.md
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## waitgroup
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[sync.WaitGroup](https://golang.org/pkg/sync/#WaitGroup) решает задачу ожидания завершения всех горутин из набора.
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### Что нужно сделать?
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Нужно написать реализацию WaitGroup используя каналы.
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Использование пакета [sync](https://golang.org/pkg/sync) в этой задаче запрещено!
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```go
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type WaitGroup struct {}
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func (wg *WaitGroup) Add(delta int) {}
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func (wg *WaitGroup) Done() {}
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func (wg *WaitGroup) Wait() {}
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```
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`WaitGroup` можно представлять себе как число.
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* При инициализации переменной типа `WaitGroup` число равно нулю.
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* Вызов `Add` прибавляет `delta` к числу.
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* Вызов `Done` вычитает из числа единицу.
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* Если при вызове `Add` или `Done` число становится отрицательным, происходит panic.
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* Вызов `Wait` при числе равном нулю -- это no-op.
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* Вызов `Wait` при числе большем нуля блокируется до тех пор, пока число не станет равным нулю.
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`WaitGroup` может быть "переиспользована".
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После достижения нуля можно вызвать `Add` заблокировав последующий `Wait`.
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43
waitgroup/waitgroup.go
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43
waitgroup/waitgroup.go
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// +build !solution
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package waitgroup
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// A WaitGroup waits for a collection of goroutines to finish.
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// The main goroutine calls Add to set the number of
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// goroutines to wait for. Then each of the goroutines
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// runs and calls Done when finished. At the same time,
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// Wait can be used to block until all goroutines have finished.
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type WaitGroup struct {
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}
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// New creates WaitGroup.
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func New() *WaitGroup {
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return nil
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}
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// Add adds delta, which may be negative, to the WaitGroup counter.
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// If the counter becomes zero, all goroutines blocked on Wait are released.
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// If the counter goes negative, Add panics.
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//
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// Note that calls with a positive delta that occur when the counter is zero
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// must happen before a Wait. Calls with a negative delta, or calls with a
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// positive delta that start when the counter is greater than zero, may happen
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// at any time.
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// Typically this means the calls to Add should execute before the statement
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// creating the goroutine or other event to be waited for.
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// If a WaitGroup is reused to wait for several independent sets of events,
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// new Add calls must happen after all previous Wait calls have returned.
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// See the WaitGroup example.
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func (wg *WaitGroup) Add(delta int) {
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}
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// Done decrements the WaitGroup counter by one.
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func (wg *WaitGroup) Done() {
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}
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// Wait blocks until the WaitGroup counter is zero.
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func (wg *WaitGroup) Wait() {
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}
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81
waitgroup/waitgroup_test.go
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81
waitgroup/waitgroup_test.go
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package waitgroup
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import (
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"sync/atomic"
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"testing"
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)
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func testWaitGroup(t *testing.T, wg1 *WaitGroup, wg2 *WaitGroup) {
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n := 16
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wg1.Add(n)
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wg2.Add(n)
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exited := make(chan bool, n)
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for i := 0; i != n; i++ {
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go func() {
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wg1.Done()
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wg2.Wait()
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exited <- true
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}()
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}
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wg1.Wait()
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for i := 0; i != n; i++ {
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select {
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case <-exited:
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t.Fatal("WaitGroup released group too soon")
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default:
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}
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wg2.Done()
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}
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for i := 0; i != n; i++ {
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<-exited // Will block if barrier fails to unlock someone.
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}
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}
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func TestWaitGroup(t *testing.T) {
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wg1 := New()
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wg2 := New()
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// Run the same test a few times to ensure barrier is in a proper state.
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for i := 0; i != 8; i++ {
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testWaitGroup(t, wg1, wg2)
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}
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}
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func TestWaitGroupMisuse(t *testing.T) {
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defer func() {
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err := recover()
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if err != "negative WaitGroup counter" {
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t.Fatalf("Unexpected panic: %#v", err)
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}
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}()
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wg := New()
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wg.Add(1)
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wg.Done()
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wg.Done()
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t.Fatal("Should panic")
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}
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func TestWaitGroupRace(t *testing.T) {
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// Run this test for about 1ms.
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for i := 0; i < 1000; i++ {
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wg := New()
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n := new(int32)
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// spawn goroutine 1
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wg.Add(1)
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go func() {
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atomic.AddInt32(n, 1)
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wg.Done()
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}()
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// spawn goroutine 2
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wg.Add(1)
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go func() {
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atomic.AddInt32(n, 1)
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wg.Done()
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}()
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// Wait for goroutine 1 and 2
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wg.Wait()
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if atomic.LoadInt32(n) != 2 {
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t.Fatal("Spurious wakeup from Wait")
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}
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}
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}
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