dotcloud/docker

package stats // import "github.com/docker/docker/daemon/stats"

import (
    "sync"
    "time"

    containertypes "github.com/docker/docker/api/types/container"
    "github.com/docker/docker/container"
    "github.com/moby/pubsub"
)

// Collector manages and provides container resource stats
type Collector struct {
    m          sync.Mutex
    cond       *sync.Cond
    supervisor supervisor
    interval   time.Duration
    publishers map[*container.Container]*pubsub.Publisher
}

// NewCollector creates a stats collector that will poll the supervisor with the specified interval
func NewCollector(supervisor supervisor, interval time.Duration) *Collector {
    s := &Collector{
        interval:   interval,
        supervisor: supervisor,
        publishers: make(map[*container.Container]*pubsub.Publisher),
    }
    s.cond = sync.NewCond(&s.m)
    return s
}

type supervisor interface {
    // GetContainerStats collects all the stats related to a container
    GetContainerStats(container *container.Container) (*containertypes.StatsResponse, error)
}

// Collect registers the container with the collector and adds it to
// the event loop for collection on the specified interval returning
// a channel for the subscriber to receive on.
func (s *Collector) Collect(c *container.Container) chan interface{} {
    s.cond.L.Lock()
    defer s.cond.L.Unlock()

    publisher, exists := s.publishers[c]
    if !exists {
        publisher = pubsub.NewPublisher(100*time.Millisecond, 1024)
        s.publishers[c] = publisher
    }

    s.cond.Broadcast()
    return publisher.Subscribe()
}

// StopCollection closes the channels for all subscribers and removes
// the container from metrics collection.
func (s *Collector) StopCollection(c *container.Container) {
    s.m.Lock()
    if publisher, exists := s.publishers[c]; exists {
        publisher.Close()
        delete(s.publishers, c)
    }
    s.m.Unlock()
}

// Unsubscribe removes a specific subscriber from receiving updates for a container's stats.
func (s *Collector) Unsubscribe(c *container.Container, ch chan interface{}) {
    s.m.Lock()
    publisher := s.publishers[c]
    if publisher != nil {
        publisher.Evict(ch)
        if publisher.Len() == 0 {
            delete(s.publishers, c)
        }
    }
    s.m.Unlock()
}

// Run starts the collectors and will indefinitely collect stats from the supervisor
func (s *Collector) Run() {
    type publishersPair struct {
        container *container.Container
        publisher *pubsub.Publisher
    }
    // we cannot determine the capacity here.
    // it will grow enough in first iteration
    var pairs []publishersPair

    for {
        s.cond.L.Lock()
        for len(s.publishers) == 0 {
            s.cond.Wait()
        }

        // it does not make sense in the first iteration,
        // but saves allocations in further iterations
        pairs = pairs[:0]

        for container, publisher := range s.publishers {
            // copy pointers here to release the lock ASAP
            pairs = append(pairs, publishersPair{container, publisher})
        }

        s.cond.L.Unlock()

        for _, pair := range pairs {
            stats, err := s.supervisor.GetContainerStats(pair.container)
            if err != nil {
                stats = &containertypes.StatsResponse{
                    Name: pair.container.Name,
                    ID:   pair.container.ID,
                }
            }
            pair.publisher.Publish(*stats)
        }

        time.Sleep(s.interval)
    }
}