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// Copyright 2017 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 semaphore_test
import (
"context"
"math/rand"
"runtime"
"sync"
"testing"
"time"
"golang.org/x/sync/errgroup"
"golang.org/x/sync/semaphore"
)
const maxSleep = 1 * time.Millisecond
func HammerWeighted(sem *semaphore.Weighted, n int64, loops int) {
for i := 0; i < loops; i++ {
sem.Acquire(context.Background(), n)
time.Sleep(time.Duration(rand.Int63n(int64(maxSleep/time.Nanosecond))) * time.Nanosecond)
sem.Release(n)
}
}
func TestWeighted(t *testing.T) {
t.Parallel()
n := runtime.GOMAXPROCS(0)
loops := 10000 / n
sem := semaphore.NewWeighted(int64(n))
var wg sync.WaitGroup
wg.Add(n)
for i := 0; i < n; i++ {
i := i
go func() {
defer wg.Done()
HammerWeighted(sem, int64(i), loops)
}()
}
wg.Wait()
}
func TestWeightedPanic(t *testing.T) {
t.Parallel()
defer func() {
if recover() == nil {
t.Fatal("release of an unacquired weighted semaphore did not panic")
}
}()
w := semaphore.NewWeighted(1)
w.Release(1)
}
func TestWeightedTryAcquire(t *testing.T) {
t.Parallel()
ctx := context.Background()
sem := semaphore.NewWeighted(2)
tries := []bool{}
sem.Acquire(ctx, 1)
tries = append(tries, sem.TryAcquire(1))
tries = append(tries, sem.TryAcquire(1))
sem.Release(2)
tries = append(tries, sem.TryAcquire(1))
sem.Acquire(ctx, 1)
tries = append(tries, sem.TryAcquire(1))
want := []bool{true, false, true, false}
for i := range tries {
if tries[i] != want[i] {
t.Errorf("tries[%d]: got %t, want %t", i, tries[i], want[i])
}
}
}
func TestWeightedAcquire(t *testing.T) {
t.Parallel()
ctx := context.Background()
sem := semaphore.NewWeighted(2)
tryAcquire := func(n int64) bool {
ctx, cancel := context.WithTimeout(ctx, 10*time.Millisecond)
defer cancel()
return sem.Acquire(ctx, n) == nil
}
tries := []bool{}
sem.Acquire(ctx, 1)
tries = append(tries, tryAcquire(1))
tries = append(tries, tryAcquire(1))
sem.Release(2)
tries = append(tries, tryAcquire(1))
sem.Acquire(ctx, 1)
tries = append(tries, tryAcquire(1))
want := []bool{true, false, true, false}
for i := range tries {
if tries[i] != want[i] {
t.Errorf("tries[%d]: got %t, want %t", i, tries[i], want[i])
}
}
}
func TestWeightedDoesntBlockIfTooBig(t *testing.T) {
t.Parallel()
const n = 2
sem := semaphore.NewWeighted(n)
{
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
go sem.Acquire(ctx, n+1)
}
g, ctx := errgroup.WithContext(context.Background())
for i := n * 3; i > 0; i-- {
g.Go(func() error {
err := sem.Acquire(ctx, 1)
if err == nil {
time.Sleep(1 * time.Millisecond)
sem.Release(1)
}
return err
})
}
if err := g.Wait(); err != nil {
t.Errorf("semaphore.NewWeighted(%v) failed to AcquireCtx(_, 1) with AcquireCtx(_, %v) pending", n, n+1)
}
}
// TestLargeAcquireDoesntStarve times out if a large call to Acquire starves.
// Merely returning from the test function indicates success.
func TestLargeAcquireDoesntStarve(t *testing.T) {
t.Parallel()
ctx := context.Background()
n := int64(runtime.GOMAXPROCS(0))
sem := semaphore.NewWeighted(n)
running := true
var wg sync.WaitGroup
wg.Add(int(n))
for i := n; i > 0; i-- {
sem.Acquire(ctx, 1)
go func() {
defer func() {
sem.Release(1)
wg.Done()
}()
for running {
time.Sleep(1 * time.Millisecond)
sem.Release(1)
sem.Acquire(ctx, 1)
}
}()
}
sem.Acquire(ctx, n)
running = false
sem.Release(n)
wg.Wait()
}
// translated from https://github.com/zhiqiangxu/util/blob/master/mutex/crwmutex_test.go#L43
func TestAllocCancelDoesntStarve(t *testing.T) {
sem := semaphore.NewWeighted(10)
// Block off a portion of the semaphore so that Acquire(_, 10) can eventually succeed.
sem.Acquire(context.Background(), 1)
// In the background, Acquire(_, 10).
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
go func() {
sem.Acquire(ctx, 10)
}()
// Wait until the Acquire(_, 10) call blocks.
for sem.TryAcquire(1) {
sem.Release(1)
runtime.Gosched()
}
// Now try to grab a read lock, and simultaneously unblock the Acquire(_, 10) call.
// Both Acquire calls should unblock and return, in either order.
go cancel()
err := sem.Acquire(context.Background(), 1)
if err != nil {
t.Fatalf("Acquire(_, 1) failed unexpectedly: %v", err)
}
sem.Release(1)
}
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