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pool.go
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pool.go
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/*
Copyright 2019 The Knative Authors
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
https://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 pool
import (
"sync"
)
type impl struct {
wg sync.WaitGroup
workCh chan func() error
// Ensure that we Wait exactly once and memoize
// the result.
waitOnce sync.Once
// We're only interested in the first result so
// only set it once.
resultOnce sync.Once
result error
}
// impl implements Interface
var _ Interface = (*impl)(nil)
// DefaultCapacity is the number of work items or errors that we
// can queue up before calls to Go will block, or work will
// block until Wait is called.
const DefaultCapacity = 50
// New creates a fresh worker pool with the specified size.
func New(workers int) Interface {
return NewWithCapacity(workers, DefaultCapacity)
}
// NewWithCapacity creates a fresh worker pool with the specified size.
func NewWithCapacity(workers, capacity int) Interface {
i := &impl{
workCh: make(chan func() error, capacity),
}
// Start a go routine for each worker, which:
// 1. reads off of the work channel,
// 2. (optionally) sends errors on the error channel,
// 3. marks work as done in our sync.WaitGroup.
for idx := 0; idx < workers; idx++ {
go func() {
for work := range i.workCh {
func() {
defer i.wg.Done()
if err := work(); err != nil {
i.resultOnce.Do(func() {
i.result = err
})
}
}()
}
}()
}
return i
}
// Go implements Interface.
func (i *impl) Go(w func() error) {
// Increment the amount of outstanding work we're waiting on.
i.wg.Add(1)
// Send the work along the queue.
i.workCh <- w
}
// Wait implements Interface.
func (i *impl) Wait() error {
i.waitOnce.Do(func() {
// Wait for queued work to complete.
i.wg.Wait()
// Now we know there are definitely no new items arriving.
close(i.workCh)
})
return i.result
}