path: root/event/example_feed_test.go

// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package event_test

import (
    "fmt"

    "github.com/ethereum/go-ethereum/event"
)

func ExampleFeed_acknowledgedEvents() {
    // This example shows how the return value of Send can be used for request/reply
    // interaction between event consumers and producers.
    var feed event.Feed
    type ackedEvent struct {
        i   int
        ack chan<- struct{}
    }

    // Consumers wait for events on the feed and acknowledge processing.
    done := make(chan struct{})
    defer close(done)
    for i := 0; i < 3; i++ {
        ch := make(chan ackedEvent, 100)
        sub := feed.Subscribe(ch)
        go func() {
            defer sub.Unsubscribe()
            for {
                select {
                case ev := <-ch:
                    fmt.Println(ev.i) // "process" the event
                    ev.ack <- struct{}{}
                case <-done:
                    return
                }
            }
        }()
    }

    // The producer sends values of type ackedEvent with increasing values of i.
    // It waits for all consumers to acknowledge before sending the next event.
    for i := 0; i < 3; i++ {
        acksignal := make(chan struct{})
        n := feed.Send(ackedEvent{i, acksignal})
        for ack := 0; ack < n; ack++ {
            <-acksignal
        }
    }
    // Output:
    // 0
    // 0
    // 0
    // 1
    // 1
    // 1
    // 2
    // 2
    // 2
}