// NewPool generates an instance of ants pool.
func NewPool(size int, options ...Option) (*Pool, error) {
    opts := loadOptions(options...)

    if size <= 0 {
        size = -1
    }

    if expiry := opts.ExpiryDuration; expiry < 0 {
        return nil, ErrInvalidPoolExpiry
    } else if expiry == 0 {
        opts.ExpiryDuration = DefaultCleanIntervalTime
    }

    if opts.Logger == nil {
        opts.Logger = defaultLogger
    }

    p := &Pool{
        capacity: int32(size),
        lock:     internal.NewSpinLock(),
        options:  opts,
    }
    p.workerCache.New = func() interface{} {
        return &goWorker{
            pool: p,
            task: make(chan func(), workerChanCap),
        }
    }
    if p.options.PreAlloc {
        if size == -1 {
            return nil, ErrInvalidPreAllocSize
        }
        p.workers = newWorkerArray(loopQueueType, size)
    } else {
        p.workers = newWorkerArray(stackType, 0)
    }

    p.cond = sync.NewCond(p.lock)

    // Start a goroutine to clean up expired workers periodically.
    go p.purgePeriodically()

    return p, nil
}

type goWorker struct {
    //work的所屬者
    pool *Pool

    //任務通道，通過這個發(fā)送給goWorker
    task chan func()

    //將work放入到隊列時更新
    recycleTime time.Time
}

type workerArray interface {
    len() int
    isEmpty() bool
    insert(worker *goWorker) error
    detach() *goWorker
    retrieveExpiry(duration time.Duration) []*goWorker
    reset()
}

func (p *Pool) retrieveWorker() (w *goWorker) {
    spawnWorker := func() {
        w = p.workerCache.Get().(*goWorker)
        w.run()
    }

    p.lock.Lock()

    w = p.workers.detach()
    if w != nil { // first try to fetch the worker from the queue
        p.lock.Unlock()
    } else if capacity := p.Cap(); capacity == -1 || capacity > p.Running() {
        // if the worker queue is empty and we don't run out of the pool capacity,
        // then just spawn a new worker goroutine.
        p.lock.Unlock()
        spawnWorker()
    } else { // otherwise, we'll have to keep them blocked and wait for at least one worker to be put back into pool.
        if p.options.Nonblocking {
            p.lock.Unlock()
            return
        }
    retry:
        if p.options.MaxBlockingTasks != 0 && p.blockingNum >= p.options.MaxBlockingTasks {
            p.lock.Unlock()
            return
        }
        p.blockingNum++
        p.cond.Wait() // block and wait for an available worker
        p.blockingNum--
        var nw int
        if nw = p.Running(); nw == 0 { // awakened by the scavenger
            p.lock.Unlock()
            if !p.IsClosed() {
                spawnWorker()
            }
            return
        }
        if w = p.workers.detach(); w == nil {
            if nw < capacity {
                p.lock.Unlock()
                spawnWorker()
                return
            }
            goto retry
        }

        p.lock.Unlock()
    }
    return
}

func (w *goWorker) run() {
    w.pool.incRunning()
    go func() {

        for f := range w.task {
            if f == nil {
                return
            }
            f()
            if ok := w.pool.revertWorker(w); !ok {
                return
            }
        }
    }()
}

p.workerCache.New = func() interface{} {
        return &goWorker{
            pool: p,
            task: make(chan func(), workerChanCap),
        }
    }

// workerChanCap determines whether the channel of a worker should be a buffered channel
    // to get the best performance. Inspired by fasthttp at
    // https://github.com/valyala/fasthttp/blob/master/workerpool.go#L139
    workerChanCap = func() int {
        // Use blocking channel if GOMAXPROCS=1.
        // This switches context from sender to receiver immediately,
        // which results in higher performance (under go1.5 at least).
        if runtime.GOMAXPROCS(0) == 1 {
            return 0
        }

        // Use non-blocking workerChan if GOMAXPROCS>1,
        // since otherwise the sender might be dragged down if the receiver is CPU-bound.
        return 1
    }()