ref: 628efd6e293d27984a3f5ba33522f8edd19d69d6
parent: 2dcc1318d1d9ed849d040115aa5ba6191a1c102a
author: Bjørn Erik Pedersen <bjorn.erik.pedersen@gmail.com>
date: Thu Nov 21 13:38:14 EST 2019
common/para: Add parallel task executor helper Usage of this will come later.
--- /dev/null
+++ b/common/para/para.go
@@ -1,0 +1,73 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package para implements parallel execution helpers.
+package para
+
+import (
+ "context"
+
+ "golang.org/x/sync/errgroup"
+)
+
+// Workers configures a task executor with the most number of tasks to be executed in parallel.
+type Workers struct {+ sem chan struct{}+}
+
+// Runner wraps the lifecycle methods of a new task set.
+//
+// Run wil block until a worker is available or the context is cancelled,
+// and then run the given func in a new goroutine.
+// Wait will wait for all the running goroutines to finish.
+type Runner interface {+ Run(func() error)
+ Wait() error
+}
+
+type errGroupRunner struct {+ *errgroup.Group
+ w *Workers
+ ctx context.Context
+}
+
+func (g *errGroupRunner) Run(fn func() error) {+ select {+ case g.w.sem <- struct{}{}:+ case <-g.ctx.Done():
+ return
+ }
+
+ g.Go(func() error {+ err := fn()
+ <-g.w.sem
+ return err
+ })
+}
+
+// New creates a new Workers with the given number of workers.
+func New(numWorkers int) *Workers {+ return &Workers{+ sem: make(chan struct{}, numWorkers),+ }
+}
+
+// Start starts a new Runner.
+func (w *Workers) Start(ctx context.Context) (Runner, context.Context) {+ g, ctx := errgroup.WithContext(ctx)
+ return &errGroupRunner{+ Group: g,
+ ctx: ctx,
+ w: w,
+ }, ctx
+}
--- /dev/null
+++ b/common/para/para_test.go
@@ -1,0 +1,85 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package para
+
+import (
+ "context"
+ "sort"
+ "sync"
+ "sync/atomic"
+ "testing"
+ "time"
+
+ qt "github.com/frankban/quicktest"
+)
+
+func TestPara(t *testing.T) {+
+ c := qt.New(t)
+
+ c.Run("Order", func(c *qt.C) {+ n := 500
+ ints := make([]int, n)
+ for i := 0; i < n; i++ {+ ints[i] = i
+ }
+
+ p := New(4)
+ r, _ := p.Start(context.Background())
+
+ var result []int
+ var mu sync.Mutex
+ for i := 0; i < n; i++ {+ i := i
+ r.Run(func() error {+ mu.Lock()
+ defer mu.Unlock()
+ result = append(result, i)
+ return nil
+ })
+ }
+
+ c.Assert(r.Wait(), qt.IsNil)
+ c.Assert(result, qt.HasLen, len(ints))
+ c.Assert(sort.IntsAreSorted(result), qt.Equals, false, qt.Commentf("Para does not seem to be parallel"))+ sort.Ints(result)
+ c.Assert(result, qt.DeepEquals, ints)
+
+ })
+
+ c.Run("Time", func(c *qt.C) {+ const n = 100
+
+ p := New(5)
+ r, _ := p.Start(context.Background())
+
+ start := time.Now()
+
+ var counter int64
+
+ for i := 0; i < n; i++ {+ r.Run(func() error {+ atomic.AddInt64(&counter, 1)
+ time.Sleep(1 * time.Millisecond)
+ return nil
+ })
+ }
+
+ c.Assert(r.Wait(), qt.IsNil)
+ c.Assert(counter, qt.Equals, int64(n))
+ c.Assert(time.Since(start) < n/2*time.Millisecond, qt.Equals, true)
+
+ })
+
+}