mhupman/ctx

Composable utilities for Go contexts

ctx

Composable utilities for Go contexts.

Installation

go get -u github.com/SentimensRG/ctx

Features

Ctx

General context / done-channel utilities

The ctx package provides utilites for working with data structures satisfying the ctx.Doner interface, most notably context.Context:

type Doner interface {
    Done() <-chan struct{}
}

The functions in ctx are appropriate for operations that do not preserve the values in a context, e.g.: joining several contexts together.

SigCtx

Go contexts for graceful shutdown

The sigctx package provides a context that terminates when it receives a SIGINT or SIGTERM. This provides a convenient mechanism for triggering graceful application shutdown.

Usage

sigctx.New returns a plain-old context.Context.

import (
    "log"
    "github.com/SentimensRG/ctx/sigctx"
)

func main() {
    ctx := sigctx.New()  // returns a regular context.Context

    <-ctx.Done()  // will unblock on SIGINT and SIGTERM
    log.Println("exiting.")    
}

RefCtx

Contextualized reference counting

The refctx package provides a context whose lifetime is bound to a RefCtr instance. The RefCtr keeps track of how many references to a context are held and cancels this context when the refcount reaches zero.

Usage

refctx works similarly to sync.WaitGroup.

package main

import "github.com/SentimensRG/ctx/refctx"

func main() {
    ctx, ctr := refctx.WithRefCount(context.Background())

    for i := 0; i < 5; i++ {
        ctr.Incr()
        go func() {
            defer ctr.Decr()

            time.Sleep(time.Second * i)
        }()
    }

    <-ctx.Done()  // fires when refcount falls back to zero    
}

A common use-case for refctx is to manage timeouts. Consider the following example using github.com/gorilla/websocket.

import (
    "time"

    "github.com/SentimensRG/ctx/refctx"
    "github.com/SentimensRG/ctx/sigctx"

    "github.com/gorilla/websocket"
)

const (
    pingDeadline = time.Second * 1
    pongDeadline = pingDeadline * 2
)

func main() {

    conn := openWebsocketConnection()

    ctx, ctr := refctx.WithRefCount(sigctx.New())  // good place for sigctx
    rc.Incr()  // start with one refcount

    go func() {
        for range time.NewTicker(heartbeatInterval).C {
            select {
            case <-c.Done():
                // c.Done fires either when the process receives an OS signal, or
                // when the peer took too long to respond to a ping.
                return
            default:
                deadline := time.Now().Add(pingDeadline)
		_ = conn.WriteControl(websocket.PingMessage, nil, deadline)
				go func() {
					<-time.After(pongDeadline)
					rc.Decr()
				}()
            }
        }
    }()

    conn.SetPongHandler(func(_ string) (_ error) {
		rc.Incr()
		return
	})

    businessLogic(c, conn)
    <-c.Done()
}

RFC

If you find this useful please let me know: l.thibault@sentimens.com

Seriously, even if you just used it in your weekend project, I'd like to hear about it :)

License

The MIT License

Copyright (c) 2017 Sentimens Research Group, LLC

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.