source: code/trunk/ring.go@ 50

package jounce

import (
        "gopkg.in/irc.v3"
)

// Ring implements a single producer, multiple consumer ring buffer. The ring
// buffer size is fixed. The ring buffer is stored in memory.
type Ring struct {
        buffer   []*irc.Message
        cap, cur uint64

        consumers []RingConsumer
}

func NewRing(capacity int) *Ring {
        return &Ring{
                buffer: make([]*irc.Message, capacity),
                cap:    uint64(capacity),
        }
}

func (r *Ring) Produce(msg *irc.Message) {
        i := int(r.cur % r.cap)
        r.buffer[i] = msg
        r.cur++
}

func (r *Ring) Consumer() *RingConsumer {
        return &RingConsumer{
                ring: r,
                cur:  0, // r.cur
        }
}

type RingConsumer struct {
        ring *Ring
        cur  uint64
}

func (rc *RingConsumer) Diff() uint64 {
        if rc.cur > rc.ring.cur {
                panic("jounce: consumer cursor greater than producer cursor")
        }
        return rc.ring.cur - rc.cur
}

func (rc *RingConsumer) Peek() *irc.Message {
        diff := rc.Diff()
        if diff == 0 {
                return nil
        }
        if diff > rc.ring.cap {
                // Consumer drops diff - cap entries
                rc.cur = rc.ring.cur - rc.ring.cap
        }
        i := int(rc.cur % rc.ring.cap)
        msg := rc.ring.buffer[i]
        if msg == nil {
                panic("jounce: unexpected nil ring buffer entry")
        }
        return msg
}

func (rc *RingConsumer) Consume() *irc.Message {
        msg := rc.Peek()
        if msg != nil {
                rc.cur++
        }
        return msg
}