src/pkg/sync/waitgroup_test.go

// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package sync_test

import (
	"runtime"
	. "sync"
	"sync/atomic"
	"testing"
)

func testWaitGroup(t *testing.T, wg1 *WaitGroup, wg2 *WaitGroup) {
	n := 16
	wg1.Add(n)
	wg2.Add(n)
	exited := make(chan bool, n)
	for i := 0; i != n; i++ {
		go func(i int) {
			wg1.Done()
			wg2.Wait()
			exited <- true
		}(i)
	}
	wg1.Wait()
	for i := 0; i != n; i++ {
		select {
		case <-exited:
			t.Fatal("WaitGroup released group too soon")
		default:
		}
		wg2.Done()
	}
	for i := 0; i != n; i++ {
		<-exited // Will block if barrier fails to unlock someone.
	}
}

func TestWaitGroup(t *testing.T) {
	wg1 := &WaitGroup{}
	wg2 := &WaitGroup{}

	// Run the same test a few times to ensure barrier is in a proper state.
	for i := 0; i != 8; i++ {
		testWaitGroup(t, wg1, wg2)
	}
}

func TestWaitGroupMisuse(t *testing.T) {
	defer func() {
		err := recover()
		if err != "sync: negative WaitGroup count" {
			t.Fatalf("Unexpected panic: %#v", err)
		}
	}()
	wg := &WaitGroup{}
	wg.Add(1)
	wg.Done()
	wg.Done()
	t.Fatal("Should panic")
}

func BenchmarkWaitGroupUncontended(b *testing.B) {
	type PaddedWaitGroup struct {
		WaitGroup
		pad [128]uint8
	}
	const CallsPerSched = 1000
	procs := runtime.GOMAXPROCS(-1)
	N := int32(b.N / CallsPerSched)
	c := make(chan bool, procs)
	for p := 0; p < procs; p++ {
		go func() {
			var wg PaddedWaitGroup
			for atomic.AddInt32(&N, -1) >= 0 {
				runtime.Gosched()
				for g := 0; g < CallsPerSched; g++ {
					wg.Add(1)
					wg.Done()
					wg.Wait()
				}
			}
			c <- true
		}()
	}
	for p := 0; p < procs; p++ {
		<-c
	}
}

func benchmarkWaitGroupAddDone(b *testing.B, localWork int) {
	const CallsPerSched = 1000
	procs := runtime.GOMAXPROCS(-1)
	N := int32(b.N / CallsPerSched)
	c := make(chan bool, procs)
	var wg WaitGroup
	for p := 0; p < procs; p++ {
		go func() {
			foo := 0
			for atomic.AddInt32(&N, -1) >= 0 {
				runtime.Gosched()
				for g := 0; g < CallsPerSched; g++ {
					wg.Add(1)
					for i := 0; i < localWork; i++ {
						foo *= 2
						foo /= 2
					}
					wg.Done()
				}
			}
			c <- foo == 42
		}()
	}
	for p := 0; p < procs; p++ {
		<-c
	}
}

func BenchmarkWaitGroupAddDone(b *testing.B) {
	benchmarkWaitGroupAddDone(b, 0)
}

func BenchmarkWaitGroupAddDoneWork(b *testing.B) {
	benchmarkWaitGroupAddDone(b, 100)
}

func benchmarkWaitGroupWait(b *testing.B, localWork int) {
	const CallsPerSched = 1000
	procs := runtime.GOMAXPROCS(-1)
	N := int32(b.N / CallsPerSched)
	c := make(chan bool, procs)
	var wg WaitGroup
	wg.Add(procs)
	for p := 0; p < procs; p++ {
		go wg.Done()
	}
	for p := 0; p < procs; p++ {
		go func() {
			foo := 0
			for atomic.AddInt32(&N, -1) >= 0 {
				runtime.Gosched()
				for g := 0; g < CallsPerSched; g++ {
					wg.Wait()
					for i := 0; i < localWork; i++ {
						foo *= 2
						foo /= 2
					}
				}
			}
			c <- foo == 42
		}()
	}
	for p := 0; p < procs; p++ {
		<-c
	}
}

func BenchmarkWaitGroupWait(b *testing.B) {
	benchmarkWaitGroupWait(b, 0)
}

func BenchmarkWaitGroupWaitWork(b *testing.B) {
	benchmarkWaitGroupWait(b, 100)
}