Example 1 In the below code, <-messages will block until it gets something on the channel. This prevents main() from exiting until one item is received on the channel. package main import ( "fmt" "time" ) func waitThenSend(msg chan string) { time.Sleep(2 * time.Second) msg <- "badwolf" } func main() { messages := make(chan string) // make unbuffered channel go func() { waitThenSend(messages) // make goroutine, pass in channel }() <-messages // blocks until channel receives a value fmt.Println("done") } Example 2 The below example demonstrates using a sync.WaitGroupto keep the program running until all of the goroutines have exited. Data is sent to the function via the unbuffered channel named numbers. ...

At work, I’ve been using both Golang and Ruby to render Nomad jobspec files in a consistent manner across environments. But Python is my one true love and I wanted to learn how to do it in Python. Turns out I already knew how… you can do it in Jinja2! I’ve used Jinja2 in the past a lot for Django and Ansible, so this was pretty easy to pick up. Here are some notes for future me when I want to inevitably do this again. ...

These are useful and I’m putting them here so I can find them easily wherever I am. Latency Comparison Numbers (~2012) ---------------------------------- L1 cache reference 0.5 ns Branch mispredict 5 ns L2 cache reference 7 ns 14x L1 cache Mutex lock/unlock 25 ns Main memory reference 100 ns 20x L2 cache, 200x L1 cache Compress 1K bytes with Zippy 3,000 ns 3 us Send 1K bytes over 1 Gbps network 10,000 ns 10 us Read 4K randomly from SSD* 150,000 ns 150 us ~1GB/sec SSD Read 1 MB sequentially from memory 250,000 ns 250 us Round trip within same datacenter 500,000 ns 500 us Read 1 MB sequentially from SSD* 1,000,000 ns 1,000 us 1 ms ~1GB/sec SSD, 4X memory Disk seek 10,000,000 ns 10,000 us 10 ms 20x datacenter roundtrip Read 1 MB sequentially from disk 20,000,000 ns 20,000 us 20 ms 80x memory, 20X SSD Send packet CA->Netherlands->CA 150,000,000 ns 150,000 us 150 ms Notes ----- 1 ns = 10^-9 seconds 1 us = 10^-6 seconds = 1,000 ns 1 ms = 10^-3 seconds = 1,000 us = 1,000,000 ns Credit ------ By Jeff Dean: http://research.google.com/people/jeff/ Originally by Peter Norvig: http://norvig.com/21-days.html#answers Contributions ------------- 'Humanized' comparison: https://gist.github.com/hellerbarde/2843375 Visual comparison chart: http://i.imgur.com/k0t1e.png Source: https://gist.github.com/jboner/2841832

Last week, I was working on some Python at work and I found myself wishing for an equivalent to Golang’s structs. Rather than passing in a bunch of core data types (string, dict, int, etc.) in an out of methods, I wanted to pass in a single object with predictable attributes. But…. I didn’t want to go through all the trouble of creating a class with a constructor, and passing in all the various attributes. ...

I’ve been a bit confused for a while over when a map in Golang gets created with a value of nil (its zero value) and when it does not, so I’m writing this to help me remember. Let’s look at various ways to initialize a map: package main import "fmt" func main() { m1 := map[string]string{} // initializes map m2 := make(map[string]string) // also initializes map var m3 map[string]string // does NOT initialize the map! HERE BE DRAGONS! fmt.Println(m1 == nil) // false fmt.Println(m2 == nil) // false fmt.Println(m3 == nil) // true m1["foo"] = "bar" m2["foo"] = "bar" m3["foo"] = "bar" // panics because the map is NOT initialized, i.e., map is still nil } My takeaways from this are: ...

My wife and I recently went to the Hawaiin islands for a few days for a vacatoin. Here’s what worked well and didn’t well about the trip. Resorts We stayed in resorts for the first time. This was new; normally we stay in Airbnbs or the like. Pros: Consistent experience. Clean and nice. Pools and hottubs. Safe. We felt very good leaving laptops and the like in the room. Cons: ...

Go has a built-in HTTP server in net/http. Here’s me playing around using it: package main import ( "fmt" "net/http" "strings" ) func hello(w http.ResponseWriter, req *http.Request) { fmt.Fprintf(w, "hello\n") } func details(w http.ResponseWriter, req *http.Request) { resp := []string{} resp = append(resp, "Request Details:") resp = append(resp, fmt.Sprintf("- Request proto: %s", req.Proto)) resp = append(resp, fmt.Sprintf("- Headers:")) for name, val := range req.Header { resp = append(resp, fmt.Sprintf("\t- %s: %s", name, val)) } resp = append(resp, "\n") fmt.Fprintf(w, strings.Join(resp, "\n")) } func main() { http.HandleFunc("/hello", hello) http.HandleFunc("/details", details) fmt.Println("Started.") http.ListenAndServe("127.0.0.1:9999", nil) fmt.Println("Exiting.") } The /details endpoint returns interesting stuff about the HTTP request, like its protocol and headers: ...

The other day, I was linting my Go code with golangci-lint when I got this error: File is not `goimports`-ed (goimports) I examined the file and found nothing amiss, but the linter insisted something was wrong. Eventually, I realized I had used spaces to indent the file rather than tabs. Changing the indent character to tabs fixed it. I then ran into the same error on a second file. This time, I had a comment which was wrong. There were two spaces before the first word in the comment (see below). ...

This post documents the high level concepts I need to remember about *nix Load Average. Load average can been seen in the output of uptime and top: From uptime: $ uptime 14:40 up 21 days, 21:48, 5 users, load averages: 2.63 2.75 3.45 From top: root@blog-server-2:~# top -n 1 | head -2 top - 15:28:37 up 10 days, 12:41, 1 user, load average: 0.04, 0.03, 0.00 Tasks: 95 total, 1 running, 94 sleeping, 0 stopped, 0 zombie root@blog-server-2:~# There are 3 decimal numbers shown. They present the load average over three different time scales: ...

Old and new workflows My dev workflow used to look like this: Write some code and save it Change to my Terminal window Up-arrow to find my command to run unit tests (typically make test) Press Enter Wait for tests to run and examine test output This worked pretty well, but was a lot of manual steps when you figure that I did this dozens (hundreds?) of times per day. That’s a lot of energy spent doing the same thing over and over again. ...